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1

Energy and Rate Determinations to Activate the C-C ?-BOND of Acetone by Gaseous NI^+  

NASA Astrophysics Data System (ADS)

A unique application of a custom fabricated photodissociation spectrometer permits the determination of thermodynamic properties (activation energies), reaction rates, and mechanistic details of bare metal cation mediated C-C ?-bond activation in the gas phase. Specifically, the products and rates resulting from the unimolecular decomposition of the Ni^+Acetone (Ni^+Ac) adduct are monitored after absorption of a known amount of energy. The three dissociative products which are observed in high yield are Ni^+, Ni^+CO, and CH3CO^+. The latter two fragment ions result from the activation of a C-C ?-bond. It was found that minimally 14 000 cm^{-1} of energy must be deposited into the adduct ion to induce C-C bond breakage. Preliminary results for the Ni^+ activation of the C-C ?-bond of acetone indicate that there are (at least) two low energy reaction coordinates leading to C-C bond breakage. The lower energy pathway emerges from the doublet ground state with an upper limit to the activation energy of 14 000 cm^{-1} and reaction rate ?0.14 molecules/?s. The higher energy path is assumed to be along the quartet reaction coordinate with a minimum activation energy of 18 800 cm^{-1} (relative to the ground state) and a slightly slower reaction rate.

Castleberry, Vanessa A.; Dee, S. Jason; Villarroel, Otsmar J.; Laboren, Ivanna E.; Frey, Sarah E.; Bellert, Darrin J.

2009-06-01

2

The computation of C-C and N-N bond dissociation energies for singly, doubly, and triply bonded systems  

NASA Technical Reports Server (NTRS)

The bond dissociation energies (D sub e) of C2H2, C2H4, C2H6, N2, N2H2, and N2H4 are studied at various levels of correlation treatment. The convergence of D sub e with respect to the one particle basis is studied at the single reference modified coupled-pair functional (MCPF) level. At all levels of correlation treatment, the errors in the bond dissociation energies increase with the degree of multiple bond character. The multireference configuration interaction (MRCI) D sub e values, corrected for an estimate of higher excitations, are in excellent agreement with those determined using the size extensive averaged coupled pair functional (ACPF) method. It was found that the full valence complete active space self consistent field (CASSCF)/MRCI calculations are reproduced very well by MRCI calculations based on a CASSCF calculation that includes in the active space only those electrons involved in the C-C or N-N bonds. To achieve chemical accuracy (1 kcal/mole) for the D sub e values of the doubly bonded species C2H4 and N2H2 requires one particle basis sets including up through h angular momentum functions (l = 5) and a multireference treatment of electron correlation: still higher levels of calculation are required to achieve chemical accuracy for the triply bonded species C2H2 and N2.

Langhoff, Stephen R.; Bauschlicher, Charles W., Jr.; Taylor, Peter R.

1989-01-01

3

Shorter still: compressing C-C single bonds.  

PubMed

How short can a C-C single bond get? The bonding in a set of molecules that are related structurally to previously synthesized or theoretically examined systems with short C-C bonds is investigated. According to calculations, a single C-C bond could be compressed to 1.313 Å! To the best of our knowledge, this is the shortest single C-C bond reported to date. This shortening is a consequence of a change in the C-C-C bond angle, ?, to minimize strain in the cages and an effort to offset the tension in the surrounding bridges. PMID:20718457

Martínez-Guajardo, Gerardo; Donald, Kelling J; Wittmaack, Bernard K; Vazquez, Miguel Angel; Merino, Gabriel

2010-09-17

4

HC[triple bond]P and H3C-C[triple bond]P as proton acceptors in protonated complexes containing two phosphorus bases: structures, binding energies, and spin-spin coupling constants.  

PubMed

Ab initio calculations at the MP2/aug'-cc-pVTZ level have been carried out to investigate the structures and binding energies of cationic complexes involving protonated sp, sp2, and sp3 phosphorus bases as proton donor ions and the sp-hybridized phosphorus bases H-C[triple bond]P and H3C-C[triple bond]P as proton acceptors. These proton-bound complexes exhibit a variety of structural motifs, but all are stabilized by interactions that occur through the pi cloud of the acceptor base. The binding energies of these complexes range from 6 to 15 kcal/mol. Corresponding complexes with H3C-C[triple bond]P as the proton acceptor are more stable than those with H-C[triple bond]P as the acceptor, a reflection of the greater basicity of H3C-C[triple bond]P. In most complexes with sp2- or sp3-hybridized P-H donor ions, the P-H bond lengthens and the P-H stretching frequency is red-shifted relative to the corresponding monomers. Complex formation also leads to a lengthening of the C[triple bond]P bond and a red shift of the C[triple bond]P stretching vibration. The two-bond coupling constants 2pihJ(P-P) and 2pihJ(P-C) are significantly smaller than 2hJ(P-P) and 2hJ(P-C) for complexes in which hydrogen bonding occurs through lone pairs of electrons on P or C. This reflects the absence of significant s electron density in the hydrogen-bonding regions of these pi complexes. PMID:17760429

Alkorta, Ibon; Elguero, José; Bene, Janet E Del

2007-10-01

5

The low-energy unimolecular reaction rate constants for the gas phase, Ni+-mediated dissociation of the C-C sigma bond in acetone.  

PubMed

The time dependence of the gaseous unimolecular decomposition of the jet-cooled adduct ion, Ni+-OC(CH3)2, was monitored through selective detection of the Ni+CO fragment ion. Various resolved amounts of energy in the range 15600-18800 cm(-1) were supplied to initiate the dissociation reaction through absorption of laser photons by the title molecular complex. First-order rate constants, k(E), ranged from 113000 to 55000 s(-1) and decreased with decreasing amounts of internal excitation. The energy used to initiate the reaction is well below that required to fragment C-C sigma bonds and indicates the necessity of the Ni+ cation to induce bond activation and fragmentation. These measurements are carried out in a unique apparatus and represent the first direct kinetic study of such catalytic type reactions. PMID:19725574

Castleberry, Vanessa A; Dee, S Jason; Villarroel, Otsmar J; Laboren, Ivanna E; Frey, Sarah E; Bellert, Darrin J

2009-10-01

6

C-C bond-forming desulfurizations of sulfoximines.  

PubMed

Highly substituted, enantiomerically pure azaheterocyclic ring systems play an important role in medicinal chemistry as potential peptide mimetics. Metalated 2-alkenyl sulfoximines offer an efficient entry to this class of compounds. In this paper, we describe a new means to remove the sulfonimidoyl auxiliary with concomitant formation of a C-C double bond. PMID:18712875

Reggelin, M; Slavik, S; Bühle, P

2008-09-18

7

C-C Bond Activation and Coupling of Propene Induced by la Atom  

NASA Astrophysics Data System (ADS)

A series of La(C_nH_m) complexes with n ? 6 and m ? 12 were produced by the reactions between propene and La in a supersonic molecular beam source. Their formation and structures were investigated using mass-analyzed threshold ionization (MATI) spectroscopy in combination with theoretical calculations. Previously, we identified the formation of La(C_3H_4) and H-La(C_3H_5) through dehydrogenation and metal insertion mechanisms. In this work, we will discuss the formation of La(CH_2) and La(C_4H_6) by La induced C-C bond activation and coupling. La(CH_2) is formed by the C-C bond breakage and 1,2-hydride shift of propene and is a Schrock-type carbene complex. This complex is then coupled with the C=C bond of a second propene molecule to form La(C_4H_6) by removing two hydrogen atoms. The resultant La(C_4H_6) complex was idetified in two low-energy isomeric forms: one was a metallacycle (isomer A) and the other was lanthanum trimethylenemethane (isomer B). Both La(C_4H_6) isomers are in a doublet ground state, with isomer A in C_s point group and isomer B in C_3_v. Adiabatic ionization energies and several vibrational frequencies of the two complexes were obtained from the sharp MATI spectra.

Hewage, Dilrukshi; Tao, Hong; Silva, Ruchira; Kumari, Sudesh; Yang, Dong-Sheng

2013-06-01

8

Valence Bond Interpretation of Elastic Anisotropy in B.C.C. Transition Metals.  

National Technical Information Service (NTIS)

Valence bond theory provides a practical microscopic phenomeno-logical context for interpretation of many properties of transition metals. In body centered cubic (b.c.c.) transition metals, the partition of the total bonding hybrids into nearest-neighbour...

D. R. Hay P. D. Parikh

1969-01-01

9

Recent advances in the gold-catalyzed additions to C-C multiple bonds  

PubMed Central

Summary C–O, C–N and C–C bonds are the most widespread types of bonds in nature, and are the cornerstone of most organic compounds, ranging from pharmaceuticals and agrochemicals to advanced materials and polymers. Cationic gold acts as a soft and carbophilic Lewis acid and is considered one of the most powerful activators of C–C multiple bonds. Consequently, gold-catalysis plays an important role in the development of new strategies to form these bonds in more convenient ways. In this review, we highlight recent advances in the gold-catalyzed chemistry of addition of X–H (X = O, N, C) bonds to C–C multiple bonds, tandem reactions, and asymmetric additions. This review covers gold-catalyzed organic reactions published from 2008 to the present.

Huang, He; Zhou, Yu

2011-01-01

10

Cross-coupling reactions involving metal carbene: from C?C/C-C bond formation to C-H bond functionalization.  

PubMed

Cross-coupling reactions involving metal-carbene are emerging as a new type of carbon-carbon bond-forming reaction. The aim of this JOCSynopsis is to provide an overview of the most recent development of these reactions, focusing on the use of diazo compounds (or in situ formed diazo compounds from N-tosylhydrazones) as carbene precursors. In addition, the integration of this type of reaction with C-H bond functionalization is also surveyed. PMID:24134640

Liu, Zhenxing; Wang, Jianbo

2013-10-18

11

Cleavage of C-C and C-Si ?-Bonds and Their Intramolecular Exchange.  

PubMed

C-C and C-Si ?-bonds are cleaved to undergo bond exchange when substrates equipped with cyclobutanone and silacyclobutane moieties are treated with a palladium(0) catalyst. The skeletal exchange results in construction of silabicyclo[5.2.1]decanes in a diastereoselective manner. PMID:24720573

Ishida, Naoki; Ikemoto, Wataru; Murakami, Masahiro

2014-04-23

12

Catalytic C-C bond formation via capture of hydrogenation intermediates.  

PubMed

Although catalytic hydrogenation has been practiced for over a century, use of hydrogen as a terminal reductant in catalytic C-C bond formation has been restricted to processes involving migratory insertion of carbon monoxide, e.g., alkene hydroformylation and related Fischer-Tropsch-type reactions. In an effort to develop hydrogenation as a new method for catalytic cross-coupling, a catalytic system enabling capture of hydrogenation intermediates was recently developed in our lab. These results support the feasibility of developing a broad new family of hydrogen-mediated C-C bond formations. PMID:15379581

Jang, Hye-Young; Krische, Michael J

2004-09-01

13

Palladium supported on detonation nanodiamond as a highly effective catalyst of the C=C and C?C bond hydrogenation  

Microsoft Academic Search

Palladium loaded on detonation nanodiamond was used for the first time as a catalyst for the C=C and C?C bond hydrogenation. By the example of tolane hydrogenation, the Pd(0)\\/nanodiamond was found to greatly surpass in catalytic activity other Pd(0)\\/nanocarbon catalysts.

Olga V. Turova; Eugenia V. Starodubtseva; Maxim G. Vinogradov; Viacheslav I. Sokolov; Natalya V. Abramova; Alexander E. Alexenskiy

2011-01-01

14

Formation of C-C Bonds via Iridium-Catalyzed Hydrogenation and Transfer Hydrogenation  

PubMed Central

The formation of C–C bonds via catalytic hydrogenation and transfer hydrogenation enables carbonyl and imine addition in the absence of stoichiometric organometallic reagents. In this review, iridium-catalyzed C–C bond-forming hydrogenations and transfer hydrogenations are surveyed. These processes encompass selective, atom-economic methods for the vinylation and allylation of carbonyl compounds and imines. Notably, under transfer hydrogenation conditions, alcohol dehydrogenation drives reductive generation of organoiridium nucleophiles, enabling carbonyl addition from the aldehyde or alcohol oxidation level. In the latter case, hydrogen exchange between alcohols and ?-unsaturated reactants generates electrophile–nucleophile pairs en route to products of hydro-hydroxyalkylation, representing a direct method for the functionalization of carbinol C–H bonds.

Bower, John F.; Krische, Michael J.

2011-01-01

15

C-C Bond formation catalyzed by natural gelatin and collagen proteins  

PubMed Central

Summary The activity of gelatin and collagen proteins towards C–C bond formation via Henry (nitroaldol) reaction between aldehydes and nitroalkanes is demonstrated for the first time. Among other variables, protein source, physical state and chemical modification influence product yield and kinetics, affording the nitroaldol products in both aqueous and organic media under mild conditions. Significantly, the scale-up of the process between 4-nitrobenzaldehyde and nitromethane is successfully achieved at 1 g scale and in good yield. A comparative kinetic study with other biocatalysts shows an increase of the first-order rate constant in the order chitosan < gelatin < bovine serum albumin (BSA) < collagen. The results of this study indicate that simple edible gelatin can promote C–C bond forming reactions under physiological conditions, which may have important implications from a metabolic perspective.

Kuhbeck, Dennis; Bijayi Dhar, Basab; Schon, Eva-Maria; Cativiela, Carlos; Gotor-Fernandez, Vicente

2013-01-01

16

Hydrocarbation of c?c bonds: quantification of the nucleophilic reactivity of ynamides.  

PubMed

Donor-substituted diarylcarbenium ions Ar2 CH(+) react with ynamides to give 1-amido-substituted allyl cations (?,?-unsaturated iminium ions). Kinetic studies show that these adducts, which correspond to the addition of a C?H bond across the C?C bond, are formed stepwise with initial formation of keteniminium ions and subsequent 1,3-hydride shifts. The linear correlations between the second-order rate constants (lg?k2 , 20?°C) with the electrophilicity parameters E of the diarylcarbenium ions allow us to include ynamides in our comprehensive nucleophilicity scale and thus predict potential electrophilic reaction partners. PMID:24715471

Laub, Hans A; Evano, Gwilherm; Mayr, Herbert

2014-05-01

17

Tandem application of C-C bond-forming reactions with reductive ozonolysis  

PubMed Central

Several variants of reductive ozonolysis, defined here as the in situ generation of aldehydes or ketones during ozonolytic cleavage of alkenes, are demonstrated to work effectively in tandem with a number of C-C bond-forming reactions. For reactions involving basic nucleophiles (1,2-addition of Grignard reagents, Wittig or Horner-Emmons olefinations, and directed Aldol reactions of lithium enolates) the one-pot process offers a rapid and high-yielding alternative to traditional two-step protocols.

Willand-Charnley, Rachel; Dussault, Patrick H.

2012-01-01

18

Benzaldehyde lyase-catalyzed diastereoselective C-C bond formation by simultaneous carboligation and kinetic resolution.  

PubMed

Enzymes create chiral microenvironments that may simultaneously generate several stereogenic centers in the same catalytic cycle, broadening the possibilities of biocatalysis. Benzaldehyde lyase (BAL) affords highly diastereoselective ?-hydroxy-ketones by simultaneously performing ligation and kinetic resolution of a racemic aldehyde. Thus, to the well-known enantioselective BAL-carboligation of aldehydes (C-C bond formation), another property, namely diastereoselectivity, is added in this paper for the first time. PMID:23280121

Müller, Christoph R; Pérez-Sánchez, María; Domínguez de María, Pablo

2013-03-28

19

Reversible C-C bond formation between redox-active pyridine ligands in iron complexes.  

PubMed

This manuscript describes the formally iron(I) complexes L(Me)Fe(Py-R)(2) (L(Me) = bulky ?-diketiminate; R = H, 4-tBu), in which the basal pyridine ligands preferentially accept significant unpaired spin density. Structural, spectroscopic, and computational studies on the complex with 4-tert-butylpyridine ((tBu)py) indicate that the S = 3/2 species is a resonance hybrid between descriptions as (a) high-spin iron(II) with antiferromagnetic coupling to a pyridine anion radical and (b) high-spin iron(I). When the pyridine lacks the protection of the tert-butyl group, it rapidly and reversibly undergoes radical coupling reactions that form new C-C bonds. In one reaction, the coordinated pyridine couples to triphenylmethyl radical, and in another, it dimerizes to give a pyridine-derived dianion that bridges two iron(II) ions. The rapid, reversible C-C bond formation in the dimer stores electrons from the formally reduced metal as a C-C bond in the ligands, as demonstrated by using the coupled diiron(II) complex to generate products that are known to come from iron(I) precursors. PMID:23181620

Dugan, Thomas R; Bill, Eckhard; MacLeod, K Cory; Christian, Gemma J; Cowley, Ryan E; Brennessel, William W; Ye, Shengfa; Neese, Frank; Holland, Patrick L

2012-12-19

20

A quantum chemical topological analysis of the C-C bond formation in organic reactions involving cationic species.  

PubMed

ELF topological analysis of the ionic Diels-Alder (I-DA) reaction between the N,N-dimethyliminium cation and cyclopentadiene (Cp) has been performed in order to characterise the C-C single bond formation. The C-C bond formation begins in the short range of 2.00-1.96 Åvia a C-to-C pseudoradical coupling between the most electrophilic center of the iminium cation and one of the two most nucleophilic centers of Cp. The electron density of the pseudoradical center generated at the most electrophilic carbon of the iminium cation comes mainly from the global charge transfer which takes place along the reaction. Analysis of the global reactivity indices indicates that the very high electrophilic character of the iminium cation is responsible for the negative activation energy found in the gas phase. On the other hand, the analysis of the radical P Parr functions of the iminium cation, and the nucleophilic Pk(-) Parr functions of Cp makes the characterisation of the most favourable two-center interaction along the formation of the C-C single bond possible. PMID:24901220

Domingo, Luis R; Pérez, Patricia

2014-07-21

21

Palladium(II)-catalyzed dehydrogenative cross-coupling between two C(sp3)-H bonds: unexpected C=C bond formation.  

PubMed

C=C bond construction: A palladium-catalyzed oxidative C(sp3)-H/C(sp3)-H cross-coupling is shown to forge C=C bonds rather than C(sp3)-C(sp3) bonds through reactions of indolin-2-ones or benzofuran-2-ones with O-benzoyl hydroxylamines in the absence of an added oxidant. PMID:23780778

Li, Gaocan; Qian, Shengyou; Wang, Chunxia; You, Jingsong

2013-07-22

22

Rhodium-Catalyzed C-C Bond Formation via Heteroatom-Directed C-H Bond Activation  

SciTech Connect

Once considered the 'holy grail' of organometallic chemistry, synthetically useful reactions employing C-H bond activation have increasingly been developed and applied to natural product and drug synthesis over the past decade. The ubiquity and relative low cost of hydrocarbons makes C-H bond functionalization an attractive alternative to classical C-C bond forming reactions such as cross-coupling, which require organohalides and organometallic reagents. In addition to providing an atom economical alternative to standard cross - coupling strategies, C-H bond functionalization also reduces the production of toxic by-products, thereby contributing to the growing field of reactions with decreased environmental impact. In the area of C-C bond forming reactions that proceed via a C-H activation mechanism, rhodium catalysts stand out for their functional group tolerance and wide range of synthetic utility. Over the course of the last decade, many Rh-catalyzed methods for heteroatom-directed C-H bond functionalization have been reported and will be the focus of this review. Material appearing in the literature prior to 2001 has been reviewed previously and will only be introduced as background when necessary. The synthesis of complex molecules from relatively simple precursors has long been a goal for many organic chemists. The ability to selectively functionalize a molecule with minimal pre-activation can streamline syntheses and expand the opportunities to explore the utility of complex molecules in areas ranging from the pharmaceutical industry to materials science. Indeed, the issue of selectivity is paramount in the development of all C-H bond functionalization methods. Several groups have developed elegant approaches towards achieving selectivity in molecules that possess many sterically and electronically similar C-H bonds. Many of these approaches are discussed in detail in the accompanying articles in this special issue of Chemical Reviews. One approach that has seen widespread success involves the use of a proximal heteroatom that serves as a directing group for the selective functionalization of a specific C-H bond. In a survey of examples of heteroatom-directed Rh catalysis, two mechanistically distinct reaction pathways are revealed. In one case, the heteroatom acts as a chelator to bind the Rh catalyst, facilitating reactivity at a proximal site. In this case, the formation of a five-membered metallacycle provides a favorable driving force in inducing reactivity at the desired location. In the other case, the heteroatom initially coordinates the Rh catalyst and then acts to stabilize the formation of a metal-carbon bond at a proximal site. A true test of the utility of a synthetic method is in its application to the synthesis of natural products or complex molecules. Several groups have demonstrated the applicability of C-H bond functionalization reactions towards complex molecule synthesis. Target-oriented synthesis provides a platform to test the effectiveness of a method in unique chemical and steric environments. In this respect, Rh-catalyzed methods for C-H bond functionalization stand out, with several syntheses being described in the literature that utilize C-H bond functionalization in a key step. These syntheses are highlighted following the discussion of the method they employ.

Colby, Denise; Bergman, Robert; Ellman, Jonathan

2010-05-13

23

Pd-catalyzed autotandem C-C/C-C bond-forming reactions with tosylhydrazones: synthesis of spirocycles with extended ?-conjugation.  

PubMed

A new Pd-catalyzed autotandem process is presented by the reaction of tosylhydrazones of cyclic ketones and 2,2'-dibromobiphenyls and related systems. The process involves cross-coupling with tosylhydrazone followed by an intramolecular Heck reaction and gives rise to spirocyclic structures. Noteworthy, two C-CAr bonds are formed on the hydrazonic carbon during the process. Depending on the starting dibromide, an array of spirofluorenes, spirodibenzofluorenes, spiroacridines, and spiroanthracenes have been prepared. Thus, this methodology may be applied for the preparation of interesting structures useful in the development of optoelectronic materials. PMID:24708061

Barroso, Raquel; Valencia, Rocío A; Cabal, María-Paz; Valdés, Carlos

2014-04-18

24

A Homogeneous, Recyclable Polymer Support for Rh(I)-Catalyzed C-C Bond Formation  

PubMed Central

A robust and practical polymer-supported, homogeneous, recyclable biphephos rhodium(I) catalyst has been developed for C-C bond formation reactions. Control of polymer molecular weight allowed tuning of the polymer solubility such that the polymer-supported catalyst is soluble in nonpolar solvents and insoluble in polar solvents. Using the supported rhodium catalysts, addition of aryl and vinylboronic acids to the electrophiles such as enones, aldehydes, N-sulfonyl aldimines, and alkynes occurs smoothly to provide products in high yields. Additions of terminal alkynes to enones and industrially relevant hydroformylation reactions have also been successfully carried out. Studies show that the leaching of Rh from the polymer support is low and catalyst recycle can be achieved by simple precipitation and filtration.

Jana, Ranjan; Tunge, Jon A.

2011-01-01

25

Bond activation with an apparently benign ethynyl dithiocarbamate Ar-C?C-S-C(S)NR2.  

PubMed

The hedgehog molecule: A simple ethynyl dithiocarbamate [Ar-C?C-S-C(S)NR(2)] is able to cleave a broad range of enthalpically strong ? bonds and to activate carbon dioxide and elemental sulfur. Depending on the substrate, the bond activation process involves either the existence of an equilibrium with the nonobservable mesoionic carbene isomer or the cooperation of the nucleophilic carbon-carbon triple bond and the electrophilic CS carbon atom. PMID:23210141

Ung, Gaël; Frey, Guido D; Schoeller, Wolfgang W; Bertrand, Guy

2011-10-10

26

Substituent effects in X?C?C?H⋯NH 3 (or OH 2, FH) hydrogen bonding  

NASA Astrophysics Data System (ADS)

MP2/6-31g(p,d) calculations were performed on the C?H⋯N (or O, F) hydrogen bonding between 18 substituted X?C?C?H and NH3, H2O, and HF. It was found that the Hammett-type correlation was applicable to the above systems, which indicated that the field/inductive and resonance effects could both affect the X?C?C?H⋯NH 3 (or H 2O, HF) hydrogen bonding.

Chen, Rong; Zhang, Ke-Chun; Liu, Lei; Li, Xiao-Song; Guo, Qing-Xiang

2001-04-01

27

A general nonaqueous route to binary metal oxide nanocrystals involving a C-C bond cleavage.  

PubMed

A widely applicable solvothermal route to nanocrystalline iron, indium, gallium, and zinc oxide based on the reaction between the corresponding metal acetylacetonate as metal oxide precursor and benzylamine as solvent and reactant is presented. Detailed XRD, TEM, and Raman studies prove that, with the exception of the iron oxide system, where a mixture of the two phases magnetite and maghemite is formed, only phase pure materials are obtained, gamma-Ga(2)O(3), zincite ZnO, and cubic In(2)O(3). The particle sizes lie in the range of 15-20 nm for the iron, 10-15 nm for the indium, 2.5-3.5 nm for gallium, and around 20 nm for zinc oxide. GC-MS analysis of the final reaction solution after removal of the nanoparticles showed that the composition is rather complex consisting of more than eight different organic compounds. Based on the fact that N-isopropylidenebenzylamine, 4-benzylamino-3-penten-2-one, and N-benzylacetamide were the main species found, we propose a detailed formation mechanism encompassing solvolysis of the acetylacetonate ligand, involving C-C bond cleavage, as well as ketimine and aldol-like condensation steps. PMID:15826200

Pinna, Nicola; Garnweitner, Georg; Antonietti, Markus; Niederberger, Markus

2005-04-20

28

Bond cleavage during isobutanol thermal decomposition and the breaking of C-C bonds in alcohols at high temperatures.  

PubMed

Isobutanol was thermally decomposed in a single pulse shock tube under conditions where chain processes were suppressed. The main reaction is the breaking of C-C bonds. Literature rate expressions, experimentally determined, are found in some cases to be in disagreement. The rate expressions for the decomposition processes at temperatures of 1090 to 1240 K and pressures of 1.5 and 6 atm are k(isobutanol ? isopropyl + hydroxymethyl) + k(isobutanol ? methyl + 1-hydroxypropyl-2) = 10(16.7±0.3) exp(-41097 ± 750) s(-1), where k(isobutanol ? isopropyl + hydroxymethyl) = 10(16.45 ±0.3) exp(-40910 ± 750/T) s(-1) and k(isobutanol ? methyl + 1-hydroxypropyl-2) = 10(16.38±0.3) exp(-41560 ± 750/T) s(-1). These values permit comparisons with recent estimates including those from ab initio calculations. A new procedure is presented that uses information on the kinetics of bond breaking reactions of alkanes and the effect of OH substitution to derive rate coefficients for similar reactions of alcohols. This leads to the following rate expression for the smaller alcohols, at temperatures of 1090 to 1240 K and pressures of 1.5 and 6 atm, k(ethanol ? methyl + hydroxymethyl) = 10(16.42±0.3) exp(-43496 ± 750 K/T) s(-1), k(isopropanol ? methyl + 1-hydroxyethyl) = 10(16.54±0.3) exp(-42495 ± 750 K/T) s(-1), k(n-propanol ? ethyl + hydroxymethyl) = 10(16.43±0.3) exp(-41696 ± 750 K/T) s(-1), and k(n-propanol ? methyl + 2-hydroxymethyl) = 10(16.53±0.3) exp(-42945 ± 750 K/T) s(-1). Extension of this approach to other alcohols is straightforward. The resulting correlations along with the data on dehydration of alcohols provide novel information of the kinetic stability of alcohols. PMID:23968459

Rosado-Reyes, Claudette; Tsang, Wing

2013-10-10

29

A DFT study on the NHC catalysed Michael addition of enols to ?,?-unsaturated acyl-azoliums. A base catalysed C-C bond-formation step.  

PubMed

The NHC catalysed nucleophilic additions of enols to ?,?-unsaturated acyl-azolium intermediates have been investigated using DFT methods at the MPWB1K/6-31G** computational level. In the direct and the conjugate additions, formation of a hydrogen bond (HB) with the carboxyl oxygen is not sufficient to favour the C-C bond formation as a consequence of the low nucleophilic character of enols. Interestingly, when enols form a HB with the chloride counterion, the activation energies associated with the conjugate addition decrease as a consequence of the increased nucleophilic character of enols and the increased electrophilic character of the 'acyl-azolium + Cl' ion pair. Analysis of the DFT reactivity indices allows establishing a base catalysed C-C bond-formation step promoted by the chloride counterion. PMID:24343422

Domingo, Luis R; Sáez, José A; Arnó, Manuel

2014-02-14

30

Energy pulse bonding  

NASA Technical Reports Server (NTRS)

To eliminate many of the present termination problems a technique called energy pulse bonding (EPB) was developed. The process demonstrated the capability of: (1) joining conductors without prior removal of insulations, (2) joining conductors without danger of brittle intermetallics, (3) increased joint temperature capability, (4) simultaneous formation of several bonds, (5) capability of higher joint density, and (6) a production oriented process. The following metals were successfully bonded in the solid state: copper, beryllium copper, phosphor bronze, aluminum, brass, and Kovar.

Smith, G. C.

1972-01-01

31

The Benzoyl Peroxide Promoted Dual C-C Bond Formation via Dual C-H Bond Cleavage: ?-Phenanthridinylation of Ether by Isocyanide.  

PubMed

The benzoyl peroxide-promoted ?-phenanthridinylation of ether by isocyanide is developed, proceeding through dual C-H bond cleavage and dual C-C bond formation. The procedure tolerates a series of functional groups, such as methyl, fluoro, chloro, acetyl, methoxy carbonyl, cyano, and trifluoromethyl. Thus, it represents a facile pathway leading to 6-substituted phenanthridine derivatives. The addition of radical to the isonitrile followed by a radical aromatic cyclization is involved in this transformation. PMID:24684422

Wang, Lei; Sha, Wanxing; Dai, Qiang; Feng, Xiaomei; Wu, Wenting; Peng, Haibo; Chen, Bin; Cheng, Jiang

2014-04-18

32

Mechanistic Examination of C?–C? Bond Cleavages of Tryptophan Residues during Dissociations of Molecular Peptide Radical Cations  

SciTech Connect

In this study, we used collision-induced dissociation (CID) to examine the gas-phase fragmentations of [GnW]•+ (n = 2-4) and [GXW]•+ (X = C, S, L, F, Y, Q) species. The C?–C? bond cleavage of a C-terminal decarboxylated tryptophan residue ([M - CO2]•+) can generate [M - CO2 - 116]+, [M - CO2 - 117]•+, and [1H-indole]•+ (m/z 117) species as possible product ions. Competition between the formation of [M - CO2 - 116]+ and [1H-indole]•+ systems implies the existence of a proton-bound dimer formed between the indole ring and peptide backbone. Formation of such a proton-bound dimer is facile via a protonation of the tryptophan ?-carbon atom as suggested by density functional theory (DFT) calculations. DFT calculations also suggested the initially formed ion 2--the decarboxylated species that is active against C?–C? bond cleavage -can efficiently isomerize to form a more-stable -radical isomer (ion 9) as supported by Rice-Ramsperger-Kassel-Marcus (RRKM) modeling. The C?–C? bond cleavage of a tryptophan residue also can occur directly from peptide radical cations containing a basic residue. CID of [WGnR]•+ (n = 1-3) radical cations consistently resulted in predominant formation of [M-116]+ product ions. It appears that the basic arginine residue tightly sequesters the proton and allows the charge-remote C?–C? bond cleavage to prevail over the charge-directed one. DFT calculations predicted the barrier for the former is 6.2 kcal mol -1 lower than that of the latter. Furthermore, the pathway involving a salt-bridge intermediate also was accessible during such a bond cleavage event.

Song, Tao; Ma, Ching-Yung; Chu, Ivan K.; Siu, Chi-Kit; Laskin, Julia

2013-02-14

33

Electronic effects in C-H and C-C bond activation: Reactions of excited state Cr{sup +} with propane, butane, methylpropane, and dimethylpropane  

SciTech Connect

Guided ion beam mass spectrometry is used to study the reactions of excited states of Cr{sup +} with propane, butane, methylpropane, and dimethylpropane. The effect of electronic energy as well as kinetic energy on the reactivity of atomic chromium ions is examined and reveals several interesting aspects of Cr{sup +} chemistry. The present results include the first direct evidence for reaction of the Cr{sup +}({sup 6}D) first excited state. Most interesting is the observation that the excited quartet states of Cr{sup +} react with alkanes very differently than ground-state Cr{sup +}({sup 6}S) activates only C-C bonds of alkanes, while in the present study we find that the excited Cr{sup +}({sup 6}S). Previously we found that Cr{sup +}({sup 6}S) activates only C-C bonds of alkanes, while in the present study we find that the excited Cr{sup +}({sup 4}d, {sup 4}g) states activates both C-H and C-C bonds of alkanes. The reactivity of the {sup 6}D first excited state of Cr{sup +} is similar to that of the {sup 6}S ground state. These reaction systems are currently the only examples where electronic excitation of a transition-metal ion drastically changes the products formed. 32 refs., 4 figs., 5 tabs.

Fisher, E.R.; Armentrout, P.B. [Univ. of Utah, Salt Lake City, UT (United States)

1992-03-11

34

Nitrosobenzene-Mediated C-C Bond Cleavage Reactions and Spectral Observation of an oxazetidin-4-one Ring System  

PubMed Central

While bond formation processes have traditionally garnered the attention of the chemical community, methods facilitating bond-breaking remain relatively undeveloped. We report a novel, transition metal-free oxidative C-C bond cleavage process for a broad range of ester and dicarbonyl compounds involving carbanion addition to nitrosobenzene. ReactIR experiments on the nitrosobenzene-mediated oxidative decarboxylation of esters indicate the reaction proceeds via fragmentation of a previously unobserved oxazetidin-4-one heterocycle, characterized by an intense IR stretching frequency at 1846 cm-1. These mechanistic studies have allowed further expansion of this protocol to ketone cleavage reactions of a diverse array of ?-ketoester and 1,3-diketone substrates. The conceptual and mechanistic insights offered by this study are likely to provide a platform for further development of bond-breaking methodologies.

Payette, Joshua N.; Yamamoto, Hisashi

2009-01-01

35

Nitrosobenzene-mediated C-C bond cleavage reactions and spectral observation of an oxazetidin-4-one ring system.  

PubMed

While bond formation processes have traditionally garnered the attention of the chemical community, methods facilitating bond breaking remain relatively undeveloped. We report a novel, transition-metal-free oxidative C-C bond cleavage process for a broad range of ester and dicarbonyl compounds involving carbanion addition to nitrosobenzene. ReactIR experiments on the nitrosobenzene-mediated oxidative decarboxylation of esters indicate the reaction proceeds via fragmentation of a previously unobserved oxazetidin-4-one heterocycle, characterized by an intense IR stretching frequency at 1846 cm-1. These mechanistic studies have allowed further expansion of this protocol to ketone cleavage reactions of a diverse array of beta-ketoester and 1,3-diketone substrates. The conceptual and mechanistic insights offered by this study are likely to provide a platform for further development of bond-breaking methodologies. PMID:18722431

Payette, Joshua N; Yamamoto, Hisashi

2008-09-17

36

Highly stable organic monolayers for reacting silicon with further functionalities: the effect of the C-C bond nearest the silicon surface.  

PubMed

Crystalline Si(111) surfaces have been alkylated in a two-step chlorination/alkylation process using various organic molecules having similar backbones but differing in their C-C bond closest to the silicon surface (i.e., C-C vs C=C vs C[triple bond]C bonds). X-ray photoelectron spectroscopic (XPS) data show that functionalization of silicon surfaces with propenyl magnesium bromide (CH3-CH=CH-MgBr) organic molecules gives nearly full coverage of the silicon atop sites, as on methyl- and propynyl-terminated silicon surfaces. Propenyl-terminated silicon surface shows less surface oxidation and is more robust against solvent attacks when compared to methyl- and propynyl-terminated silicon surfaces. We also show a secondary functionalization process of propenyl-terminated silicon surface with 4'-[3-Trifluoromethyl-3H-diazirin-3-yl]-benzoic acid N-hydroxysuccinimide ester [TDBA-OSu] cross-linker. The Si-CH=CH-CH3 surfaces thus offer a means of attaching a variety of chemical moieties to a silicon surface through a short linking group, enabling applications in molecular electronics, energy conversion, catalysis, and sensing. PMID:18803387

Puniredd, Sreenivasa Reddy; Assad, Ossama; Haick, Hossam

2008-10-15

37

Copper-Catalyzed Oxidative Cyclization of 1,5-Enynes with Concomitant C-C Bond Cleavage: An Unexpected Access to 3-Formyl-1-indenone Derivatives.  

PubMed

A Cu(0)/Selectfluor system-mediated oxidative cyclization of 1,5-enynes with concomitant C-C bond cleavage to access 3-formyl-1-indenone derivatives is described. Preliminary mechanistic investigations disclosed that the C-C bond cleavage involved a novel water-participated oxygen-insertion ?-carbon elimination through double oxycuprations. PMID:24807823

Zhang, Jian; Wu, Degui; Chen, Xiaoling; Liu, Yunkui; Xu, Zhenyuan

2014-06-01

38

Unlocking Hydrogenation for C-C Bond Formation: A Brief Overview of Enantioselective Methods  

PubMed Central

Hydrogenation of ?-unsaturated reactants in the presence of carbonyl compounds or imines promotes reductive C-C coupling, providing a byproduct-free alternative to stoichiometric organometallic reagents in an ever-increasing range of C=X (X = O, NR) additions. Under transfer hydrogenation conditions, hydrogen exchange between alcohols and ?-unsaturated reactants triggers generation of electrophile-nucleophile pairs, enabling carbonyl addition directly from the alcohol oxidation level, bypassing discrete alcohol oxidation and generation of stoichiometric byproducts.

Hassan, Abbas; Krische, Michael J.

2011-01-01

39

Ternary Electrocatalysts for Oxidizing Ethanol to Carbon Dioxide: Making Ir Capable of Splitting C-C bond  

SciTech Connect

Splitting the C-C bond is the main obstacle to electroxidation of ethanol (EOR) to CO2. We recently demonstrated that the ternary PtRhSnO2 electrocatalyst can accomplish that reaction at room temperature with Rh having a unique capability to split the C-C bond. In this article we report the finding that Ir can be induced to split the C-C bond as a component of the ternary catalyst. We synthesized, characterized and compared the properties of several ternary electrocatalysts. Carbon-supported nanoparticle (NP) electrocatalysts comprising a SnO2 NP core decorated with multi-metallic nanoislands (MM = PtIr, PtRh, IrRh, PtIrRh) were prepared using a seeded growth approach. An array of characterization techniques were employed to establish the composition and architecture of the synthesized MM /SnO2 NPs, while electrochemical and in situ infrared reflection absorption spectroscopy studies elucidated trends in activity and the nature of the reaction intermediates and products. Both EOR reactivity and selectivity towards CO2 formation of several of these MM /SnO2/C electrocatalysts are significantly higher compared to conventional Pt/C and Pt/SnO2/C catalysts. We demonstrate that the PtIr/SnO2/C catalyst with high Ir content shows outstanding catalytic property with the most negative EOR onset potential and reasonably good selectivity towards ethanol complete oxidation to CO2. PtRh/SnO2/C catalysts with a moderate Rh content exhibit the highest EOR selectivity, as deduced from infrared studies.

Li, Meng [Brookhaven National Laboratory (BNL); Cullen, David A [ORNL; Sasaki, Kotaro [Brookhaven National Laboratory (BNL); Marinkovic, N. [University of Delaware; More, Karren Leslie [ORNL; Adzic, Radoslav R. [Brookhaven National Laboratory (BNL)

2013-01-01

40

C?C Bond activation with selective functionalization: preparation of unsymmetrical biaryls from benzonitriles  

Microsoft Academic Search

For the first time, benzonitriles have been shown to participate in metal-catalyzed cross coupling reactions via activation of the C?CN bond. Thus, reaction of a benzonitrile with an aryl Grignard derivative in the presence of a Ni catalyst can readily provide the corresponding unsymmetrical biaryl in high yield and with high selectivity.

Joseph A. Miller

2001-01-01

41

Substituent effect on reactivity of triplet excited state of 2,3-diazabicyclo[2.2.1]hept-2-enes, DBH derivatives: ? C-N bond cleavage versus ? C-C bond cleavage.  

PubMed

The photoreaction of a series of 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH) derivatives, in which various substituents (X) were introduced at the methano bridge carbon of C(7), was investigated under direct (>290 nm) and triplet-sensitized (Ph2CO, >370 nm) irradiation conditions of the azo chromophore (?C?–C?–N?N–C?–C??). The azo compounds offered a unique opportunity to see the substituent X effect at the remote position of the azo chromophore on the reactivity of the triplet excited state of bicyclic azoalkanes. The present study led to the first observation of the unusual C?–C? bond-cleavage reaction without the ring stiffness, that is, the structural rigidity, in the triplet state of the cyclic azoalkanes. The stereoelectronic effects were found to play an important role in lowering the activation energy of the C?–C? bond-cleavage reaction. NBO analyses at the M06-2X/cc-PVDZ level of theory confirmed the stereoelectronic effect. PMID:22985271

Abe, Manabu; Watanabe, Shinji; Tamura, Hiroshi; Boinapally, Srikanth; Kanahara, Kousei; Fujiwara, Yoshihisa

2013-03-01

42

Oxidative addition of the C?-C? bond in ?-O-4 linkage of lignin to transition metals using a relativistic pseudopotential-based ccCA-ONIOM method.  

PubMed

A multi-level multi-layer QM/QM method, the relativistic pseudopotential correlation-consistent composite approach within an ONIOM framework (rp-ccCA-ONIOM), was applied to study the oxidative addition of the C(?)-C(?) bond in an archetypal arylglycerol ?-aryl ether (?-O-4 linkage) substructure of lignin to Ni, Cu, Pd and Pt transition metal atoms. The chemically active high-level layer is treated using the relativistic pseudopotential correlation-consistent composite approach (rp-ccCA), an efficient methodology designed to reproduce an accuracy that would be obtained using the more computationally demanding CCSD(T)/aug-cc-pCV?Z-PP, albeit at a significantly reduced computational cost, while the low-level layer is computed using B3LYP/cc-pVTZ. The thermodynamic and kinetic feasibilities of the model reactions are reported in terms of enthalpies of reactions at 298 K (?H°(298)) and activation energies (?H-act). The results obtained from the rp-ccCA:B3LYP hybrid method are compared to the corresponding values using CCSD(T) and several density functionals including B3LYP, M06, M06 L, B2PLYP, mPWPLYP and B2GP-PLYP. The energetics of the oxidative addition of C?C bond in ethane to Ni, Cu, Pd and Pt atoms are also reported to demonstrate that the rp-ccCA method effectively reproduces the accuracy of the CCSD(T)/aug-cc-pCV?Z method. Our results show that in the catalytic activation of the C(?)-C(?) bond of ?-O-4, the use of platinum metal catalysts will lead to the most thermodynamically favored reaction with the lowest activation barrier. PMID:22144374

Oyedepo, Gbenga A; Wilson, Angela K

2011-12-01

43

Metal-catalyzed C-C bond cleavage in alkanes: effects of methyl substitution on transition-state structures and stability.  

PubMed

Methyl substituents at C-C bonds influence hydrogenolysis rates and selectivities of acyclic and cyclic C2-C8 alkanes on Ir, Rh, Ru, and Pt catalysts. C-C cleavage transition states form via equilibrated dehydrogenation steps that replace several C-H bonds with C-metal bonds, desorb H atoms (H*) from saturated surfaces, and form ? H2(g) molecules. Activation enthalpies (?H(?)) and entropies (?S(?)) and ? values for (3)C-(x)C cleavage are larger than for (2)C-(2)C or (2)C-(1)C bonds, irrespective of the composition of metal clusters or the cyclic/acyclic structure of the reactants. (3)C-(x)C bonds cleave through ?,?,?- or ?,?,?,?-bound transition states, as indicated by the agreement between measured activation entropies and those estimated for such structures using statistical mechanics. In contrast, less substituted C-C bonds involve ?,?-bound species with each C atom bound to several surface atoms. These ?,? configurations weaken C-C bonds through back-donation to antibonding orbitals, but such configurations cannot form with (3)C atoms, which have one C-H bond and thus can form only one C-M bond. (3)C-(x)C cleavage involves attachment of other C atoms, which requires endothermic C-H activation and H* desorption steps that lead to larger ?H(?) values but also larger ?S(?) values (by forming more H2(g)) than for (2)C-(2)C and (2)C-(1)C bonds, irrespective of alkane size (C2-C8) or cyclic/acyclic structure. These data and their mechanistic interpretation indicate that low temperatures and high H2 pressures favor cleavage of less substituted C-C bonds and form more highly branched products from cyclic and acyclic alkanes. Such interpretations and catalytic consequences of substitution seem also relevant to C-X cleavage (X = S, N, O) in desulfurization, denitrogenation, and deoxygenation reactions. PMID:24961991

Flaherty, David W; Hibbitts, David D; Iglesia, Enrique

2014-07-01

44

Regioselective [2 + 2] cycloaddition of a fullerene dimer with an alkyne triggered by thermolysis of an interfullerene C-C bond.  

PubMed

Heating of a singly bonded fullerene dimer in the presence of an alkyne forms a cyclobutene structure on only one of the two fullerene moieties, through a stereo- and regioselective [2 + 2] cycloaddition. Experimental and theoretical data suggest that the reaction is triggered by cleavage of the interfullerene C-C bond and formation of a monomeric fullerene radical. PMID:23611627

Xiao, Zuo; Matsuo, Yutaka; Maruyama, Masashi; Nakamura, Eiichi

2013-05-01

45

A quantum chemical study of the C-C bond fission pathways of alkoxy radicals formed following OH addition to isoprene  

SciTech Connect

Isoprene is one of the most important non-methane organic compounds in tropospheric chemistry, yet its atmospheric degradation pathways remain incompletely understood. The uncertain fates of alkoxy radicals formed in the first stages of the OH-initiated degradation of isoprene contribute significantly to ignorance. This paper examines the C-C bond fission pathways of these radicals at the B3LYP/6-311G(2df,2p) level of theory. For the four {beta}-hydroxyalkoxy radicals that are expected to be formed, C-C bond fission (decomposition) pathways exist with very low barriers (0.7--2.1 kcal/mol) that are likely to dominate the chemistry. These radicals appear to possess intramolecular hydrogen bonds which typically persist in the transition states. For the two {delta}-hydroxyalkoxy radicals formed, C-C bond fission is endothermic (16--20 kcal/mol) and this pathway is unlikely to be important.

Dibble, T.S.

1999-10-21

46

Bonding and Integration of C-C Composite to Cu-Clad-Molybdenum for Thermal Management Applications  

NASA Technical Reports Server (NTRS)

Two- and three-dimensional carbon-carbon composites with either resin-derived matrix or CVI matrix were joined to Cu-clad-Mo using active Ag-Cu braze alloys for thermal management applications. The joint microstructure and composition were examined using Field-Emission Scanning Electron Microscopy and Energy-Dispersive Spectroscopy, and the joint hardness was characterized using the Knoop microhardness testing. Observations on the infiltration of the composite with molten braze, dissolution of metal substrate, and solute segregation at the C-C surface have been discussed. The thermal response of the integrated assembly is also briefly discussed.

Asthana, R.; Singh, M.; Shpargel, T.P.

2008-01-01

47

Active Metal Brazing and Adhesive Bonding of Titanium to C/C Composites for Heat Rejection System  

NASA Technical Reports Server (NTRS)

Robust assembly and integration technologies are critically needed for the manufacturing of heat rejection system (HRS) components for current and future space exploration missions. Active metal brazing and adhesive bonding technologies are being assessed for the bonding of titanium to high conductivity Carbon-Carbon composite sub components in various shapes and sizes. Currently a number of different silver and copper based active metal brazes and adhesive compositions are being evaluated. The joint microstructures were examined using optical microscopy, and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). Several mechanical tests have been employed to ascertain the effectiveness of different brazing and adhesive approaches in tension and in shear that are both simple and representative of the actual system and relatively straightforward in analysis. The results of these mechanical tests along with the fractographic analysis will be discussed. In addition, advantages, technical issues and concerns in using different bonding approaches will also be presented.

Singh, M.; Shpargel, Tarah; Cerny, Jennifer

2006-01-01

48

A new 3-(phenylseleno)allylic cation: its regioselective C-C bond formation reaction with nucleophiles.  

PubMed

Highly useful C-C bond formation using 2-ethoxy-3-(phenylseleno)prop-2-enal acetal 2 was examined with various Lewis acids. The reaction of 2 with the silyl enol ether in the presence of BF(3)*Et2O, ZnBr2, or SnBr4 regioselectively provided (Z)-3,4-diethoxy-5-(phenylseleno)pent-4-enophenone 5a in high yields. On the other hand, the reaction with other Lewis acids such as EtAlCl2 or SnCl4 gave 5-(phenylseleno)- 6 or non-selenopentane-1,4-dione 7, respectively. Novel prop-2-enal acetals 2-4 and 13-15 reacted with various nucleophiles to give pent-4-enophenones 5a,b, 10a, 12, and 16-18, S-ethyl pent-4-enoate 5b, alkylated vinylic sulfide 10b, 3-pentenenitrile 5d, and 10c. A versatile pent-4-enophenone 5a could be converted to tetrahydrofuran 20 and penta-2,4-dienophenone 19, the Diels-Alder reactions of which with dienophiles gave the adducts 24 and 25. PMID:11846647

Hibino, Masaru; Koike, Tomoko; Yoshimatsu, Mitsuhiro

2002-02-22

49

Twinning and multiaxial cyclic plasticity of a low stacking-fault-energy F. C. C. alloy  

SciTech Connect

Out-of-phase cyclic tension and torsion tests followed by metallographic measurements are carried out on Co33Ni specimens. It appears that, even for small strain ranges, nonproportional loadings induce profuse mechanical twinning and a strong kinematic hardening in this low stacking-fault-energy f.c.c. alloy. These results are analyzed and an attempt to incorporate twinning into micromechanical simulations of f.c.c. polycrystals elastoplastic behaviour is described.

Doquet, V. (Ecole Polytechnique, Palaiseau (France). Lab. de Mecanique des Solides)

1993-08-01

50

C-H Bond activation and C-C bond formation in the reaction of 2,5-dimethylthiophene with TpMe2Ir compounds.  

PubMed

The bulky 2,5-dimethylthiophene (2,5-Me2T) reacts at 60 degrees C with TpMe2Ir(C2H4)2 to give a mixture of two TpMe2Ir(III) hydride products, 3 and 4, that contain in addition a thienyl (3) or a thienyl-derived ligand (4). For the generation of 3 only sp2 C-H activation is needed, but the formation of 4 requires also the activation of an sp3 C-H bond and the formation of a new C-C bond (between vinyl and thienyl fragments). In the presence of 2,5-Me2T, compound 4 reacts further to produce a complex thiophenic structure (5, characterized by X-ray methods) that derives formally from two molecules of 2,5-Me2T and a vinyl fragment. Compounds 3-5 can be readily protonated by [H(OEt2)2][BAr'4](Ar'= 3,5-C6H3(CF3)2), with initial generation of carbene ligands (in the case of 3 and 5) as a consequence of H+ attack at the beta-carbon of the Ir-thienyl unit. Free, substituted thiophenes, derived from the original 2,5-Me2T, may be isolated in this way. PMID:15824780

Paneque, Margarita; Poveda, Manuel L; Carmona, Ernesto; Salazar, Verónica

2005-04-21

51

Solar energy assisted starch-stabilized palladium nanoparticles and their application in C-C coupling reactions.  

PubMed

Present work reports a novel one step, greener protocol for the synthesis of starch-stabilized palladium nanoparticles (PdNPs) with an average particle diameter of 30-40 nm. These particles were stable and uniform in size. In present protocol, the concentrated solar energy mediated reduction of palladium chloride was achieved by using citric acid as a reducing agent and starch as a capping agent. UV-Visible spectroscopy, Transmission Electron Microscopy, Field Emission Gun-Scanning Electron Microscopy, Selected Area Electron Diffraction and Electron dispersive X-ray Spectral analysis techniques were used to characterize this starch capped PdNPs. Herein; we are reporting such combination of starch and citric acid in the synthesis of PdNPs for the first time. The catalytic activity of synthesized nanoparticles has been checked for Suzuki and Heck cross coupling reactions. The product yield was confirmed by GC. The products were confirmed using GC-MS analysis and also using GC with the help of authentic standards. Solar energy assisted starch stabilized PdNPs showed excellent activity in the C-C bond formation between aryl halides (I, Br) with phenyl boronic acid and its derivatives. In addition, the catalyst showed good activity in the Heck coupling reaction of C-C bond formation of aryl halides with aromatic alkene. The use of starch, citric acid, water and solar energy makes present protocol greener. PMID:23901531

Patil, Aniruddha B; Bhanage, Bhalchandra M

2013-07-01

52

Water promoted C-C bond cleavage: facile synthesis of 3,3-bipyrrole derivatives from dienones and tosylmethyl isocyanide (TosMIC).  

PubMed

A simple and highly efficient synthetic strategy to access 3,3-bipyrrole derivatives by the reaction of dienone derivatives with TosMIC is reported. The reaction involves a van Leusen's pyrrole synthesis followed by an unusual C-C bond cleavage in the presence of water under mild conditions. PMID:24493005

Wang, Rong; Wang, Shun-Yi; Ji, Shun-Jun

2014-03-21

53

Highly Stereoselective C--C Bond Formation by Rhodium-Catalyzed Tandem Ylide Formation/[2,3]-Sigmatropic Rearrangement Between Donor/Acceptor Carbenoids and Chiral Allylic Alcohols  

PubMed Central

The tandem ylide-formation/[2,3]-sigmatropic rearrangement between donor/acceptor rhodium-carbenoids and chiral allyl alcohols is a convergent C—C bond forming process, which generates two vicinal stereogenic centers. Any of the four possible stereoisomers can be selectively synthesized by appropriate combination of the chiral catalyst Rh2(DOSP)4 and the chiral alcohol.

Li, Zhanjie; Parr, Brendan T.; Davies, Huw M. L.

2012-01-01

54

Design of leaving groups in radical c?c fragmentations: through-bond 2c-3e interactions in self-terminating radical cascades.  

PubMed

Radical cascades terminated by ?-scission of exocyclic C?C bonds allow for the formation of aromatic products. Whereas ?-scission is common for weaker bonds, achieving this reactivity for carbon-carbon bonds requires careful design of radical leaving groups. It has now been found that the energetic penalty for breaking a strong ?-bond can be compensated by the gain of aromaticity in the product and by the stabilizing two-center, three-electron "half-bond" present in the radical fragment. Furthermore, through-bond communication of a radical and a lone pair accelerates the fragmentation by selectively stabilizing the transition state. The stereoelectronic design of radical leaving groups leads to a new, convenient route to Sn-functionalized aromatics. PMID:24898770

Mondal, Sayantan; Gold, Brian; Mohamed, Rana K; Alabugin, Igor V

2014-07-01

55

Mechanism-based inhibition of HsaD: a C-C bond hydrolase essential for survival of Mycobacterium tuberculosis in macrophage.  

PubMed

Mycobacterium tuberculosis remains the leading cause of death by a bacterial pathogen worldwide. Increasing prevalence of multidrug-resistant organisms means prioritizing identification of targets for antituberculars. 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate hydrolase (HsaD), part of the cholesterol metabolism operon, is vital for survival within macrophage. The C-C bond hydrolase, HsaD, has a serine protease-like catalytic triad. We tested a range of serine protease and esterase inhibitors for their effects on HsaD activity. As well as providing a potential starting point for drug development, the data provides evidence for the mechanism of C-C bond hydrolysis. This screen also provides a route to initiate development of fragment-based inhibitors. PMID:24164668

Ryan, Ali; Keany, Sebastian; Eleftheriadou, Olga; Ballet, Romain; Cheng, Hung-Yuan; Sim, Edith

2014-01-01

56

NAD(P)H-independent asymmetric C=C bond reduction catalyzed by ene reductases by using artificial co-substrates as the hydrogen donor.  

PubMed

To develop a nicotinamide-independent single flavoenzyme system for the asymmetric bioreduction of C=C bonds, four types of hydrogen donor, encompassing more than 50 candidates, were investigated. Six highly potent, cheap, and commercially available co-substrates were identified that (under the optimized conditions) resulted in conversions and enantioselectivities comparable with, or even superior to, those obtained with traditional two-enzyme nicotinamide adenine dinucleotide phosphate (NAD(P)H)-recycling systems. PMID:24382795

Winkler, Christoph K; Clay, Dorina; Entner, Marcello; Plank, Markus; Faber, Kurt

2014-01-27

57

An approach to benzophosphole oxides through silver- or manganese-mediated dehydrogenative annulation involving C-C and C-P bond formation.  

PubMed

Benzophosphole construction was achieved through the Ag(I) -mediated dehydrogenative annulation of phenylphosphine oxides with internal alkynes in a process involving C?C and C?P bond formation. A wide range of asymmetrical phenylacetylenes could be employed and the reactions proceeded with perfect regioselectivity. Moreover, the annulation could be conducted even at room temperature when a Mn(III) promoter was used in place of Ag(I) . PMID:24127410

Unoh, Yuto; Hirano, Koji; Satoh, Tetsuya; Miura, Masahiro

2013-12-01

58

Oxidative C(sp(3))-H bond cleavage, C-C and C[double bond, length as m-dash]C coupling at a boron center with O2 as the oxidant mediated by platinum(ii).  

PubMed

Dimethyl- and diphenylplatinum(ii) fragments Pt(II)R2 (R = Me, Ph) enable facile and efficient oxidative C(sp(3))-H bond cleavage and stepwise C-C and C[double bond, length as m-dash]C coupling at the boron atom of a coordinated 1,5-cyclooctanediyldi(2-pyridyl)borato ligand with O2 as the sole oxidant. PMID:24287586

Pal, S; Zavalij, P Y; Vedernikov, A N

2014-05-25

59

Accurate In Bond Energies  

NASA Technical Reports Server (NTRS)

InXn atomization energies are computed for n = 1-3 and X = H, Cl, and CH3. The geometries and frequencies are determined using density functional theory. The atomization energies are computed at the coupled cluster level of theory. The complete basis set limit is obtained by extrapolation. The scalar relativistic effect is computed using the Douglas-Kroll approach. While the heats of formation for InH, InCl and InCl3 are in good agreement with experiment, the current results show that the experimental value for In(CH3)3 must be wrong.

Bauschlicher, Charles W., Jr.; Arnold, James O. (Technical Monitor)

1999-01-01

60

Microstructure dependence and origin of local energy release in b c c technical superconductors during strain  

Microsoft Academic Search

Dynamic stress effects in b c c technical superconductors NbTi and NbZr were studied using two measuring techniques. In short sample training experiments the load at which normal transition due to instantaneous local energy release occurred in successive straining cycles was measured. The acoustic emission was monitored during strain at 4.2 K and is explained by a stress induced shear

G. Pasztor; C. Schmidt

1981-01-01

61

Active Metal Brazing and Adhesive Bonding of Titanium to C/C Composites for Heat Rejection System.  

National Technical Information Service (NTIS)

Robust assembly and integration technologies are critically needed for the manufacturing of heat rejection system (HRS) components for current and future space exploration missions. Active metal brazing and adhesive bonding technologies are being assessed...

M. Singh T. Shpargel J. Cerny

2006-01-01

62

Photodissociation Dynamics of 2-BROMOETHYLNITRITE at 351 NM and C-C Bond Fission in the ? - Radical Product  

NASA Astrophysics Data System (ADS)

We used a crossed laser-molecular beam scattering experiment to investigate the primary photodissociation channels of bromoethylnitrite at 351 nm. Only the O-NO bond fission channel forming the ? -bromoethoxy radical and NO, no HBr photoelimination, was detected upon 351 nm photoexcitation,. The subsequent decomposition of the highly vibrational excited ? -bromoethoxy radical to formaldehyde + CH{_2}Br was also investigated.

Wang, Lei; Chhantyal-Pun, Rabi; Brynteson, Matt D.; Miller, Terry A.; Butler, Laurie J.

2013-06-01

63

Computational Study of Low-Temperature Catalytic C-C Bond Activation of Alkanes for Portable Power.  

National Technical Information Service (NTIS)

The development of a room temperature (<50 C) fuel cell that would use a generally available fuel such as JP8 would be most valuable. However there are no known catalysts that can selectively activate the CC bonds of such fuels at such temperature. The go...

2013-01-01

64

Synthesis of 1-amino-2-aroyl/acetylnaphthalenes through a base mediated one pot inter and intramolecular C-C bond formation strategy.  

PubMed

A new precursor 2-(1-cyano-2,2-bis(methylthio)vinyl)benzonitrile has been synthesized by the reaction of 2-cyanomethylbenzonitrile, carbon disulfide and methyl iodide under basic conditions. The reaction of 2-(1-cyano-2,2-bis(methylthio)vinyl)benzonitrile with various functionalized aryl/heteroaryl methyl ketones or acetone under basic conditions afforded 4-amino-3-aroyl/heteroaroyl/acetyl-2-methylsulfanylnaphthalene-1-carbonitriles in good yields through a (5C + 1C) annulation strategy; this involves sequential intermolecular, followed by intramolecular, C-C bond formation reactions. The structure of the product was confirmed by single crystal X-ray crystallography. PMID:24871917

Singh, Surjeet; Yadav, Pratik; Sahu, Satya Narayan; Althagafi, Ismail; Kumar, Abhinav; Kumar, Brijesh; Ram, Vishnu Ji; Pratap, Ramendra

2014-06-11

65

Structural and mechanistic studies of Pd-catalyzed C C bond formation: The case of carbonylation and Heck reaction  

Microsoft Academic Search

The extraordinary catalytic activity of palladium in CC bond forming processes is reviewed in respect to Heck and carbonylation reactions. Examples of catalytic systems based on palladium complexes with phosphorus ligands and phosphine-free systems and based on the Pd(0) colloid are presented. The two key steps of both reaction mechanisms: first, reduction of Pd(II) to Pd(0) complexes or Pd(0) colloids

Anna M. Trzeciak; Józef J. Zió?kowski

2005-01-01

66

C?-C? chromophore bond dissociation in protonated tyrosine-methionine, methionine-tyrosine, tryptophan-methionine, methionine-tryptophan and their sulfoxide analogs.  

PubMed

C(?)-C(?) chromophore bond dissociation in some selected methionine-containing dipeptides induced by UV photons is investigated. In methionine containing dipeptides with tryptophan as the UV chromophore, the tryptophan side chain is ejected either as an ion or as a neutral fragment while in dipeptides with tyrosine, the tyrosine side chain is lost only as a neutral fragment. Mechanisms responsible for these fragmentations are proposed based on measured branching ratios and fragmentation times, and on the results of DFT/B3-LYP calculations. It appears that the C(?)-C(?) bond cleavage is a non-statistical dissociation for the peptides containing tyrosine, and occurs after internal conversion for those with tryptophan. The proposed mechanisms are governed by the ionization potential of the aromatic side chain compared to that of the rest of the molecule, and by the proton affinity of the aromatic side chain compared to that of the methionine side chain. In tyrosine-containing peptides, the presence of oxygen on sulfur of methionine presumably reduces the ionization potential of the peptide backbone, facilitating the loss of the side chain as a neutral fragment. In tryptophan-containing peptides, the presence of oxygen on methionyl-sulfur expedites the transfer of the proton from the side chain to the sulfoxide, which facilitates the loss of the neutral side chain. PMID:22722478

Sunil Kumar, S; Lucas, B; Soorkia, S; Barat, M; Fayeton, J A

2012-08-01

67

Reactivity of Biomimetic Iron(II)-2-aminophenolate Complexes toward Dioxygen: Mechanistic Investigations on the Oxidative C-C Bond Cleavage of Substituted 2-Aminophenols.  

PubMed

The isolation and characterization of a series of iron(II)-2-aminophenolate complexes [(6-Me3-TPA)Fe(II)(X)](+) (X = 2-amino-4-nitrophenolate (4-NO2-HAP), 1; X = 2-aminophenolate (2-HAP), 2; X = 2-amino-3-methylphenolate (3-Me-HAP), 3; X = 2-amino-4-methylphenolate (4-Me-HAP), 4; X = 2-amino-5-methylphenolate (5-Me-HAP), 5; X = 2-amino-4-tert-butylphenolate (4-(t)Bu-HAP), 6 and X = 2-amino-4,6-di-tert-butylphenolate (4,6-di-(t)Bu-HAP), 7) and an iron(III)-2-amidophenolate complex [(6-Me3-TPA)Fe(III)(4,6-di-(t)Bu-AP)](+) (7(Ox)) supported by a tripodal nitrogen ligand (6-Me3-TPA = tris(6-methyl-2-pyridylmethyl)amine) are reported. Substituted 2-aminophenols were used to prepare the biomimetic iron(II) complexes to understand the effect of electronic and structural properties of aminophenolate rings on the dioxygen reactivity and on the selectivity of C-C bond cleavage reactions. Crystal structures of the cationic parts of 5·ClO4 and 7·BPh4 show six-coordinate iron(II) centers ligated by a neutral tetradentate ligand and a monoanionic 2-aminophenolate in a bidentate fashion. While 1·BPh4 does not react with oxygen, other complexes undergo oxidative transformation in the presence of dioxygen. The reaction of 2·ClO4 with dioxygen affords 2-amino-3H-phenoxazin-3-one, an auto-oxidation product of 2-aminophenol, whereas complexes 3·BPh4, 4·BPh4, 5·ClO4 and 6·ClO4 react with O2 to exhibit C-C bond cleavage of the bound aminophenolates. Complexes 7·ClO4 and 7(Ox)·BPh4 produce a mixture of 4,6-di-tert-butyl-2H-pyran-2-imine and 4,6-di-tert-butyl-2-picolinic acid. Labeling experiments with (18)O2 show the incorporation of one oxygen atom from dioxygen into the cleavage products. The reactivity (and stability) of the intermediate, which directs the course of aromatic ring cleavage reaction, is found to be dependent on the nature of ring substituent. The presence of two tert-butyl groups on the aminophenolate ring in 7·ClO4 makes the complex slow to cleave the C-C bond of 4,6-di-(t)Bu-HAP, whereas 4·BPh4 containing 4-Me-HAP displays fastest reactivity. Density functional theory calculations were conducted on [(6-Me3-TPA)Fe(III)(4-(t)Bu-AP)](+) (6(Ox)) to gain a mechanistic insight into the regioselective C-C bond cleavage reaction. On the basis of the experimental and computational studies, an iron(II)-2-iminobenzosemiquinonate intermediate is proposed to react with dioxygen resulting in the oxidative C-C bond cleavage of the coordinated 2-aminophenolates. PMID:24787025

Chakraborty, Biswarup; Bhunya, Sourav; Paul, Ankan; Paine, Tapan Kanti

2014-05-19

68

Heme Carbonyls: Environmental Effects on ?C–O and Fe-C/C-O Bond Length Correlations  

PubMed Central

The synthesis and characterization of four low-spin (carbonyl)iron(II) tetraphenylporphyrinates, [Fe(TPP)(CO)(L)], where L = 1-methylimidazole, 2-methylimidazole, 1,2-dimethylimidazole (unsolvated) and 1,2-dimethylimidazole (toluene solvate) are reported. The complexes show nearly the same value of ?C–O in toluene solution (1969–72 cm?1) but a large range of CO stretching frequencies in the solid-state (1926–1968 cm?1). The large solid-state variation results from CO interactions in the solid-state as shown by an examination of the crystal structures of the four complexes. The high precision of the four structures obtained allows us to make a number of structural and spectroscopic correlations that describe the Fe–C–O and NIm–Fe–CO units. The values of ?C–O and the Fe–C and C–O bond distances are strongly correlated and provide a structural as well as a spectroscopic correlation of the ? back-bonding model. The interactions of CO described are closely related to the large range of CO stretching frequencies observed in heme proteins and specific interactions observed in carbonylmyoglobin (MbCO).

Silvernail, Nathan J.; Roth, Arne; Noll, Bruce C.; Scheidt, W. Robert; Schulz, Charles E.

2006-01-01

69

Effects of alkoxy groups on arene rings of lignin ?-O-4 model compounds on the efficiencies of single electron transfer-promoted photochemical and enzymatic C-C Bond Cleavage Reactions.  

PubMed

To gain information about how alkoxy substitution in arene rings of ?-O-4 structural units within lignin governs the efficiencies/rates of radical cation C1-C2 bond cleavage reactions, single electron transfer (SET) photochemical and lignin peroxidase-catalyzed oxidation reactions of dimeric/tetrameric model compounds have been explored. The results show that the radical cations derived from less alkoxy-substituted dimeric ?-O-4 models undergo more rapid C1-C2 bond cleavage than those of more alkoxy-substituted analogues. These findings gained support from the results of DFT calculations, which demonstrate that C1-C2 bond dissociation energies of ?-O-4 radical cations decrease as the degree of alkoxy substitution decreases. In SET reactions of tetrameric compounds consisting of two ?-O-4 units, containing different degrees of alkoxy substitution, regioselective radical cation C-C bond cleavage was observed to occur in one case at the C1-C2 bond in the less alkoxy-substituted ?-O-4 moiety. However, regioselective C1-C2 cleavage in the more alkoxy-substituted ?-O-4 moiety was observed in another case, suggesting that other factors might participate in controlling this process. These observations show that lignins containing greater proportions of less rather than more alkoxylated rings as part of ?-O-4 units would be more efficiently cleaved by SET mechanisms. PMID:23992466

Lim, Suk Hyun; Nahm, Keepyung; Ra, Choon Sup; Cho, Dae Won; Yoon, Ung Chan; Latham, John A; Dunaway-Mariano, Debra; Mariano, Patrick S

2013-09-20

70

Organolanthanide-induced C-C bond formation. Preparation and properties of monomeric lanthanide aldolates and enolates  

SciTech Connect

The reactivity of early-lanthanide carbyls Cp* {sub 2}LnCH(SiMe{sub 3}){sub 2} (1, Ln = La; 2, Ln = Ce) toward ketones has been studied. No reaction was observed with the bulky di-tert-butyl ketone. The corresponding lanthanum hydride [Cp* {sub 2}LaH]{sub 2} (3) is more reactive and afforded the addition product Cp*{sub 2}LaOCH(t-Bu){sub 2}{sup center-dot}O=C(t-Bu){sub 2} (4). Hydrogen transfer and formation of lanthanide aldolates Cp* {sub 2}LnOCMe{sub 2}C(=O)Me (5, Ln = Ce; 6, Ln =La) together with the protonated carbyl CH{sub 2}(SiMe{sub 3}){sub 2} were observed when 1 or 2 was treated with acetone. The molecular structure of the cerium analogue 5 was determined by X-ray diffraction and was found to be a monomeric bent metallocene compound with a {eta}{sup 2}-coordinated aldol fragment. Addition of 3-pentanone to the carbyls 1 and 2 did not result in C-C coupling but provided enolate-ketone adducts Cp*{sub 2}LnOC(Et)=C(H)MeO=CEt{sub 2} (7, Ln = La; 8, Ln = Ce). Reactions of the carbyls 1 and 2 with 4-methyl-5-hydroxy-5ethyl-3-heptanone yielded the enolate-ketone adducts as well and suggest that the differences in reactivity between acetone and 3-pentanone are thermodynamic and not kinetic in origin. 32 refs., 2 figs., 5 tabs.

Heeres, H.J.; Maters, M.; Teuben, J.H. [Univ. of Groningen (Netherlands)] [and others

1992-01-01

71

Bis(trifluoromethyl)methylene Addition to Vinyl-Terminated SAMs: A Gas-Phase C-C Bond-Forming Reaction on a Surface  

PubMed Central

Vinyl-terminated self-assembled monolayers (SAMs) on silicon oxide substrates were chemically modified by the addition of a bis(trifluoromethyl)methylene group in a rare gas-phase C–C bond-forming reaction to directly generate films carrying terminal CF3 groups. The vinyl-terminated films were treated with hexafluoroacetone azine (HFAA) for modification. The films were characterized with ellipsometry, contact angle measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). In this study, we find that for optimized conditions clean reactions occur on a surface between SAMs with terminal olefins and HFAA, and the product is consistent with bis(trifluoromethyl)cyclopropanation formation after nitrogen extrusion.

2014-01-01

72

Bis(trifluoromethyl)methylene Addition to Vinyl-Terminated SAMs: A Gas-Phase C-C Bond-Forming Reaction on a Surface.  

PubMed

Vinyl-terminated self-assembled monolayers (SAMs) on silicon oxide substrates were chemically modified by the addition of a bis(trifluoromethyl)methylene group in a rare gas-phase C-C bond-forming reaction to directly generate films carrying terminal CF3 groups. The vinyl-terminated films were treated with hexafluoroacetone azine (HFAA) for modification. The films were characterized with ellipsometry, contact angle measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). In this study, we find that for optimized conditions clean reactions occur on a surface between SAMs with terminal olefins and HFAA, and the product is consistent with bis(trifluoromethyl)cyclopropanation formation after nitrogen extrusion. PMID:24806554

Adamkiewicz, Malgorzata; O'Hagan, David; Hähner, Georg

2014-05-20

73

Microwave and quantum chemical study of propa-1,2-dienyl thiocyanate (H2C=C=CHSC triple bond N).  

PubMed

The microwave spectrum of propa-1,2-dienyl thiocyanate (H2C=C=CHSC triple bond N) has been investigated in the 24-40 and 50-80 GHz spectral regions. The spectrum of one conformer was assigned. This rotamer, which has a C-C-S-C dihedral angle of about 134 degrees from synperiplanar, is at least 2 kJ/mol more stable than any other form. Two vibrationally excited states assumed to belong to the first excited state of the C-S torsional vibration and to a low bending mode were assigned. Their frequencies were determined to be 62(20) and 155(30) cm-1, respectively. The microwave work has been augmented by ab initio calculations at the MP2/aug-cc-pVTZ and density functional theory calculations at the B3LYP/aug-cc-pVTZ level of theory. The B3LYP calculations are generally in better agreement with the observations than the MP2 calculations. PMID:17388347

Møllendal, Harald; Cole, George C; Guillemin, Jean-Claude

2007-04-01

74

Gas-phase reactivity of lanthanide cations with fluorocarbons: C-F versus C-H and C-C bond activation  

SciTech Connect

The gas-phase reactivity of the fluorinated hydrocarbons CF{sub 4}, CHF{sub 3}, CH{sub 3}F, C{sub 2}F{sub 6}, 1,1-C{sub 2}H{sub 4}F{sub 2}, and C{sub 6}F{sub 6} with the lanthanide cations Ce{sup +}, Pr{sup +}, Sm{sup +}, Ho{sup +}, Tm{sup +}, and Yb{sup +} and the reactivity of C{sub 6}H{sub 5}F with all lanthanide cations Ln{sup +} (Ln = La-Lu, with the exception of Pm{sup +}) have been examined by Fourier-transform ion cyclotron resonance mass spectrometry. The perfluorinated compounds tetrafluoromethane and hexafluoroethane as well as trifluoromethane do not react with any lanthanide cation. Selective activation of the strong C-F bonds in fluoromethane, 1,1-difluoroethane, hexafluorobenzene, and fluorobenzene appears as a general reaction scheme along the 4f row. Experimental evidence is given for a `harpoon`-like mechanism for the F atom abstraction process which operates via an initial electron transfer from the lanthanide cation to the fluorinated substrate in the encounter complex Ln{sup +}RF. The most reactive lanthanides La{sup +}, Ce{sup +}, Gd{sup +}, and Tb{sup +} and also the formal closed-shell species Lu{sup +} exhibit additional C-H and C-C bond activation pathways in the reaction with fluorobenzene, namely dehydrohalogenation as well as loss of a neutral acetylene molecule. In the case of Tm{sup +} and Yb{sup +} the formation of neutral LnF{sub 3} is observed in a multistep process via C-C coupling and charge transfer. 17 refs., 2 figs., 2 tabs.

Cornehl, H.H.; Hornung, G.; Schwarz, H. [Technischen Unibersitaet Berlin (Germany)] [Technischen Unibersitaet Berlin (Germany)

1996-10-16

75

Reversible Sigma C-C Bond Formation Between Phenanthroline Ligands Activated by (C5Me5)2Yb.  

PubMed

The electronic structure and associated magnetic properties of the 1,10-phenanthroline adducts of Cp*2Yb are dramatically different from those of the 2,2'-bipyridine adducts. The monomeric phenanthroline adducts are ground state triplets that are based upon trivalent Yb(III), f(13), and (phen(•-) ) that are only weakly exchange coupled, which is in contrast to the bipyridine adducts whose ground states are multiconfigurational, open-shell singlets in which ytterbium is intermediate valent ( J. Am. Chem. Soc 2009 , 131 , 6480 ; J. Am. Chem. Soc 2010 , 132 , 17537 ). The origin of these different physical properties is traced to the number and symmetry of the LUMO and LUMO+1 of the heterocyclic diimine ligands. The bipy(•-) has only one ?*1 orbital of b1 symmetry of accessible energy, but phen(•-) has two ?* orbitals of b1 and a2 symmetry that are energetically accessible. The carbon p?-orbitals have different nodal properties and coefficients and their energies, and therefore their populations change depending on the position and number of methyl substitutions on the ring. A chemical ramification of the change in electronic structure is that Cp*2Yb(phen) is a dimer when crystallized from toluene solution, but a monomer when sublimed at 180-190 °C. When 3,8-Me2phenanthroline is used, the adduct Cp*2Yb(3,8-Me2phen) exists in the solution in a dimer-monomer equilibrium in which ?G is near zero. The adducts with 3-Me, 4-Me, 5-Me, 3,8-Me2, and 5,6-Me2-phenanthroline are isolated and characterized by solid state X-ray crystallography, magnetic susceptibility and LIII-edge XANES spectroscopy as a function of temperature and variable-temperature (1)H NMR spectroscopy. PMID:24852897

Nocton, Grégory; Lukens, Wayne W; Booth, Corwin H; Rozenel, Sergio S; Medling, Scott A; Maron, Laurent; Andersen, Richard A

2014-06-18

76

Low-energy reaction rate constants for the Ni+-assisted decomposition of acetaldehyde: observation of C-H and C-C activation.  

PubMed

Rate constants for the low-energy Ni(+)-assisted dissociative reaction of acetaldehyde have been measured under jet-cooled conditions in the gas phase. The rate constants are acquired through monitoring the time dependence of fragment Ni(+)CO formation. The decomposition of the precursor Ni(+)-acetaldehyde cluster ion proceeds via consecutive, parallel reaction coordinates that originate with the Ni(+)-assisted cleavage of either a C-C or an aldehyde C-H bond. The energies used to initiate these reactions are well below that required to cleave sigma-bonds in the isolated acetaldehyde molecule. Direct measurement of the reaction kinetics over a range of energies indicates that the rate-limiting step in the dissociative mechanism changes at cluster ion internal energies = 17,200 +/- 400 cm(-1). Arguments are presented that this energy marks the closure of the dissociative coordinate that initiates with C-H sigma-bond activation and thus provides a measure of the activation energy of this dissociative pathway. PMID:20050634

Dee, S Jason; Castleberry, Vanessa A; Villarroel, Otsmar J; Laboren, Ivanna E; Bellert, Darrin J

2010-02-01

77

Characterization of CF bonds with multiple-bond character: bond lengths, stretching force constants, and bond dissociation energies.  

PubMed

Isoelectronic C=F(+) and C=O bonds contained in fluoro-substituted carbenium ions, aldehydes, and ketones are investigated with regard to their bond properties by utilizing the vibrational spectra of these molecules. It is demonstrated that bond dissociation energies (BDEs), bond lengths, vibrational stretching frequencies, and bond densities are not reliable descriptors of the bond strength. The latter is related to the intrinsic BDE, which corresponds to nonrelaxed dissociation products retaining the electronic structure and geometry they have in the molecule. It is shown that the harmonic stretching force constants k(a) of the localized internal coordinate vibrations (adiabatic vibrational modes) reflect trends in the intrinsic BDEs. The k(a) values of both CO and CF bonds are related to the bond lengths through a single exponential function. This observation is used to derive a common bond order n for 46 CO- and CF-containing molecules that reliably describes differences in bonding. CF bonds in fluorinated carbenium ions possess bond orders between 1.3 and 1.7 as a result of significant pi back-bonding from F to C, which is sensitive to electronic effects caused by substituents at the carbenium center. Therefore, the strength of the C=F(+) bond can be used as a sensor for (hyper)conjugation and other electronic effects influencing the stability of the carbenium ion. The diatomic C=F(+) ion has a true double bond due to pi donation from the F atom. The characterization of CF bonds with the help of adiabatic stretching modes is also applied to fluoronium ions (n = 0.3-0.6) and transition states involving CF cleavage and HF elimination (n = 0.7-0.8). PMID:19152353

Kraka, Elfi; Cremer, Dieter

2009-03-01

78

Measuring Bond Energy of an Ionic Compound  

NSDL National Science Digital Library

In this media-rich lesson, students investigate bond energy and the law of conservation of energy. They examine the chemistry behind instant cold packs by using a calorimeter to study the endothermic dissociation of ammonium chloride in water.

2007-08-09

79

Regioselective functionalization of iminophosphoranes through Pd-mediated C-H bond activation: C-C and C-X bond formation.  

PubMed

The orthopalladation of iminophosphoranes [R(3)P=N-C(10)H(7)-1] (R(3) = Ph(3) 1, p-Tol(3) 2, PhMe(2) 3, Ph(2)Me 4, N-C(10)H(7)-1 = 1-naphthyl) has been studied. It occurs regioselectively at the aryl ring bonded to the P atom in 1 and 2, giving endo-[Pd(?-Cl)(C(6)H(4)-(PPh(2=N-1-C(10)H(7))-2)-?-C,N](2) (5) or endo-[Pd(?-Cl)(C(6)H(3)-(P(p-Tol)(2)=N-C(10)H(7)-1)-2-Me-5)-?-C,N](2) (6), while in 3 the 1-naphthyl group is metallated instead, giving exo-[Pd(?-Cl)(C(10)H(6)-(N=PPhMe(2))-8)-?-C,N](2) (7). In the case of 4, orthopalladation at room temperature affords the kinetic exo isomer [Pd(?-Cl)(C(10)H(6)-(N=PPh(2)Me)-8)-?-C,N](2) (11exo), while a mixture of 11exo and the thermodynamic endo isomer [Pd(?-Cl)(C(6)H(4)-(PPhMe=N-C(10)H(7)-1)-2)-?-C,N](2) (11endo) is obtained in refluxing toluene. The heating in toluene of the acetate bridge dimer [Pd(?-OAc)(C(10)H(6)-(N=PPh(2)Me)-8)-?-C,N](2) (13exo) promotes the facile transformation of the exo isomer into the endo isomer [Pd(?-OAc)(C(6)H(4)-(PPhMe=N-C(10)H(7)-1)-2)-?-C,N](2) (13endo), confirming that the exo isomers are formed under kinetic control. Reactions of the orthometallated complexes have led to functionalized molecules. The stoichiometric reactions of the orthometallated complexes [Pd(?-Cl)(C(10)H(6)-(N=PPhMe(2))-8)-?-C,N](2) (7), [Pd(?-Cl)(C(6)H(4)-(PPh(2)[=NPh)-2)](2) (17) and [Pd(?-Cl)(C(6)H(3)-(C(O)N=PPh(3))-2-OMe-4)](2) (18) with I(2) or with CO results in the synthesis of the ortho-halogenated compounds [PhMe(2)P=N-C(10)H(6)-I-8] (19), [I-C(6)H(4)-(PPh(2)=NPh)-2] (21) and [Ph(3)P=NC(O)C(6)H(3)-I-2-OMe-5] (23) or the heterocycles [C(10)H(6)-(N=PPhMe(2))-1-(C(O))-8]Cl (20), [C(6)H(5)-(N=PPh(2)-C(6)H(4)-C(O)-2]ClO(4) (22) and [C(6)H(3)-(C(O)-1,2-N-PPh(3))-OMe-4]Cl (24). PMID:20927428

Aguilar, David; Navarro, Rafael; Soler, Tatiana; Urriolabeitia, Esteban P

2010-11-21

80

Mild and Highly Selective Ultrasound-Promoted Zinc/Acetic Acid Reduction of C = C Bonds in alpha, Beta-Unsaturated gamma-Dicarbonyl Compounds. (Reannouncement with New Availability Information).  

National Technical Information Service (NTIS)

Sonication of various, alpha, Beta-unsaturated Gamma-diketones, quinones, alpha-Beta-unsaturated Gamma-diacids or Gamma-diesters with powdered zinc and acetic acid at room temperature results in selective reduction of the C=C bond in each case within ca. ...

A. P. Marchand M. Reddy

1991-01-01

81

Phosphine nickel complex as catalyst in reactions of organic bromides RBr with {alpha},{beta}-unsaturated ketones, nitriles, and esters. Conjugate addition of R group and H atom across the C=C bond  

SciTech Connect

Reactions of organic bromides, particularly of secondary and tertiary alkyl bromides, with {alpha},{beta}-unsaturated carbonyl compounds and acrylonitrile in the presence of the catalytic system nickel complex-zinc. The products correspond to the conjugate addition of the organic moiety of the bromide and a hydrogen atom across the C=C double bond of the unsaturated substrate. 9 refs., 1 tab.

Lebedev, S.A.; Lopatina, V.S.; Petrov, E.S.

1995-09-10

82

Bond Dissociation Energies--A Continuing Story,  

National Technical Information Service (NTIS)

Most modern bond dissociation energies are obtained from kinetic rather than thermodynamic studies. This requires assumptions sometimes explicit and sometimes implicit which always require close scrutiny. Three case histories are examined spanning the per...

S. W. Benson

1987-01-01

83

Sensitivity of a Strained C-C Single Bond to Charge Transfer: Redox Activity in Mononuclear and Dinuclear Ruthenium Complexes of Bis(arylimino)acenaphthene (BIAN) Ligands.  

PubMed

The new compounds [Ru(acac)2(BIAN)], BIAN = bis(arylimino)acenaphthene (aryl = Ph (1a), 4-MeC6H4 (2a), 4-OMeC6H4 (3a), 4-ClC6H4 (4a), 4-NO2C6H4 (5a)), were synthesized and structurally, electrochemically, spectroscopically, and computationally characterized. The ?-diimine sections of the compounds exhibit intrachelate ring bond lengths 1.304 Å < d(CN) < 1.334 and 1.425 Å < d(CC) < 1.449 Å, which indicate considerable metal-to-ligand charge transfer in the ground state, approaching a Ru(III)(BIAN(•-)) oxidation state formulation. The particular structural sensitivity of the strained peri-connecting C-C bond in the BIAN ligands toward metal-to-ligand charge transfer is discussed. Oxidation of [Ru(acac)2(BIAN)] produces electron paramagnetic resonance (EPR) and UV-vis-NIR (NIR = near infrared) spectroelectrochemically detectable Ru(III) species, while the reduction yields predominantly BIAN-based spin, in agreement with density functional theory (DFT) spin-density calculations. Variation of the substituents from CH3 to NO2 has little effect on the spin distribution but affects the absorption spectra. The dinuclear compounds {(?-tppz)[Ru(Cl)(BIAN)]2}(ClO4)2, tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine; aryl (BIAN) = Ph ([1b](ClO4)2), 4-MeC6H4 ([2b](ClO4)2), 4-OMeC6H4 ([3b](ClO4)2), 4-ClC6H4 ([4b](ClO4)2), were also obtained and investigated. The structure determination of [2b](ClO4)2 and [3b](ClO4)2 reveals trans configuration of the chloride ligands and unreduced BIAN ligands. The DFT and spectroelectrochemical results (UV-vis-NIR, EPR) indicate oxidation to a weakly coupled Ru(III)Ru(II) mixed-valent species but reduction to a tppz-centered radical state. The effect of the ? electron-accepting BIAN ancillary ligands is to diminish the metal-metal interaction due to competition with the acceptor bridge tppz. PMID:24983788

Mondal, Prasenjit; Agarwala, Hemlata; Jana, Rahul Dev; Plebst, Sebastian; Grupp, Anita; Ehret, Fabian; Mobin, Shaikh M; Kaim, Wolfgang; Lahiri, Goutam Kumar

2014-07-21

84

Adhesive bonding using variable frequency microwave energy  

SciTech Connect

Methods of facilitating the adhesive bonding of various components with variable frequency microwave energy are disclosed. The time required to cure a polymeric adhesive is decreased by placing components to be bonded via the adhesive in a microwave heating apparatus having a multimode cavity and irradiated with microwaves of varying frequencies. Methods of uniformly heating various articles having conductive fibers disposed therein are provided. Microwave energy may be selectively oriented to enter an edge portion of an article having conductive fibers therein. An edge portion of an article having conductive fibers therein may be selectively shielded from microwave energy. 26 figs.

Lauf, R.J.; McMillan, A.D.; Paulauskas, F.L.; Fathi, Z.; Wei, J.

1998-08-25

85

Adhesive bonding using variable frequency microwave energy  

SciTech Connect

Methods of facilitating the adhesive bonding of various components with variable frequency microwave energy are disclosed. The time required to cure a polymeric adhesive is decreased by placing components to be bonded via the adhesive in a microwave heating apparatus having a multimode cavity and irradiated with microwaves of varying frequencies. Methods of uniformly heating various articles having conductive fibers disposed therein are provided. Microwave energy may be selectively oriented to enter an edge portion of an article having conductive fibers therein. An edge portion of an article having conductive fibers therein may be selectively shielded from microwave energy. 26 figs.

Lauf, R.J.; McMillan, A.D.; Paulauskas, F.L.; Fathi, Z.; Wei, J.

1998-09-08

86

Adhesive bonding using variable frequency microwave energy  

DOEpatents

Methods of facilitating the adhesive bonding of various components with variable frequency microwave energy are disclosed. The time required to cure a polymeric adhesive is decreased by placing components to be bonded via the adhesive in a microwave heating apparatus having a multimode cavity and irradiated with microwaves of varying frequencies. Methods of uniformly heating various articles having conductive fibers disposed therein are provided. Microwave energy may be selectively oriented to enter an edge portion of an article having conductive fibers therein. An edge portion of an article having conductive fibers therein may be selectively shielded from microwave energy.

Lauf, Robert J. (Oak Ridge, TN); McMillan, April D. (Knoxville, TN); Paulauskas, Felix L. (Oak Ridge, TN); Fathi, Zakaryae (Cary, NC); Wei, Jianghua (Raleigh, NC)

1998-01-01

87

KO(t)Bu-mediated synthesis of dimethylisoindolin-1-ones and dimethyl-5-phenylisoindolin-1-ones: selective C-C coupling of an unreactive tertiary sp3 C-H bond.  

PubMed

A new reaction for the synthesis of dimethylisoindolinones has been presented from 2-halo-N-isopropyl-N-alkylbenzamide substrates and KO(t)Bu by the selective C-C coupling of an unreactive tertiary sp(3) C-H bond. The reaction manifested an excellent selectivity toward a tertiary sp(3) C-H bond over primary or sec C-H bond. Moreover, biaryl C-C coupling along with alkyl-aryl C-C coupling can be achieved in one pot using dihalobenzamides for the synthesis of biaryl 5-phenylisoindolin-1-ones. It seems that the reaction proceeds via a radical pathway in which the aryl radical translocates via 1,5-hydrogen atom transfer (HAT), forming a tertiary alkyl carbon-centered radical. The generated tertiary alkyl radical could attack the benzamide ring in a 5-exo/endo-trig manner followed by the release of an electron and a proton, leading to a five-membered isoindolinone ring. HAT seems to be responsible for the selective functionalization of the tertiary alkyl group over primary and secondary C-H bonds. PMID:24597670

Bhakuni, Bhagat Singh; Yadav, Abhimanyu; Kumar, Shailesh; Patel, Saket; Sharma, Shubham; Kumar, Sangit

2014-04-01

88

Electrochiroptical response of 2,2'-(2,2-diarylethenyl)binaphthyl-type electron donors that undergo reversible C-C bond formation/breaking upon two-electron transfer.  

PubMed

2,2'-[2,2-Bis(4-dimethylaminophenyl)ethenyl]biphenyl (1) is a strong electron donor that undergoes oxidative C-C bond formation to give a stable dication rac-2(2+), the 9,10-dihydrophenanthrene derivative substituted with two bis(4-dimethylaminophenyl)methylium chromophores. This dication salt regenerates the starting diolefin 1 by reductive C-C bond breaking, thus realizing a new electrochromic system with high electrochemical bistability and a vivid change in color from yellow to deep blue. Similarly, the binaphthylic diolefin rac-3 and the helicene-type dication rac-4(2+) are interconvertible upon two-electron transfer. Both the UV-vis and CD spectra changed drastically upon electrochemical transformation between optically pure 3 and 4(2+), which represents a new electrochiroptical system. PMID:12919023

Higuchi, Hiroki; Ohta, Eisuke; Kawai, Hidetoshi; Fujiwara, Kenshu; Tsuji, Takashi; Suzuki, Takanori

2003-08-22

89

Measurements of electron attachment lineshapes and cross sections at ultralow electron energies for c-C6F10, c-C6F12, C8F16 and 1,1,2-C2Cl3F3  

NASA Technical Reports Server (NTRS)

Electron attachment cross sections are reported in the electron energy range 0-160 meV and at energy resolutions of 4.5-7.5 meV (FWHM) for the molecules c-C6F10 (perfluorocyclohexene), c-C6F12 (perfluoro-1,2-dimethylcyclobutane), C8F16 (perfluoro-1,3-dimethylcyclohexane) and 1,1,2-C2Cl3F3 (1,1,2-trichlorotrifluoroethane). Use is made of the Kr photoionization technique, and measured attachment lineshapes are converted to cross sections by normalization through attachment rate constants. Comparisons are made with attachment cross sections derived from swarm-measured rate constants. Similar to previous results in eight other molecules, the present four molecules exhibit resolution-limited onsets at a threshold consistent with an s-wave attachment behavior and with a neutral-negative-ion curve crossing at zero energy.

Alajajian, S. H.; Chutjian, A.

1986-01-01

90

Silver(I) double and multiple salts containing the 1,3-butadiynediide dianion: coordination diversity and assembly with the supramolecular synthon Ag4[cap]C[triple bond]C-C[triple bond]C[cap]Ag4.  

PubMed

A series of 13 silver(I) double and multiple salts containing 1,3-butadiynediide, C4(2-), were synthesized by dissolving the silver carbide Ag2C4 in a concentrated aqueous solution of one or more of the silver salts AgNO3, AgCF3CO2, AgC2F5CO2, AgF, AgBF4, and AgPF6. The 1,3-butadiynediide anion invariably adopts a mu4,mu4 coordination mode in these compounds, which indicates that the Ag4[cap]C[triple bond]C-C[triple bond]C[cap]Ag4 moiety can be used as a new type of metalloligand supramolecular synthon for the construction of coordination networks. Fine-tuning with various ancillary anionic ligands caused the Ag4 aggregate at each ethynide terminus to adopt a butterfly-shaped, planar, or barblike configuration, within which the silver-ethynide interactions can be classified into three types: sigma, pi, and mixed (sigma,pi). The effect of coexisting nitrile ligands and quaternary ammonium salts on supramolecular assembly with the above synthon was also explored. The hydrolysis of PF6(-) and BF4(-) led to the formation of the quadruple salt Ag2C4 x 4 AgNO3 x AgPF2O2 x Ag3PO4 and a novel (F)2(H2O)18 hydrogen-bonded tape in the triple salt Ag2C4 x 2 AgF x 10 AgC2F5CO2 x CH3CN x 12 H2O, respectively. The largest silver-ethynide cluster aggregate described to date, (C4)3@Ag18, occurs in 3 Ag2C4 x 12 AgC2F5CO2 x 5 [(BnMe3N)C2F5CO2] x 4 H2O (Bn = benzyl). PMID:17768727

Zhao, Liang; Du, Miao; Mak, Thomas C W

2007-10-01

91

Bond-Energy and Surface-Energy Calculations in Metals  

ERIC Educational Resources Information Center

A simple technique appropriate for introductory materials science courses is outlined for the calculation of bond energies in metals from lattice energies. The approach is applied to body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal-closest-packed (hcp) metals. The strength of these bonds is tabulated for a variety metals and is…

Eberhart, James G.; Horner, Steve

2010-01-01

92

Primary photodissociation pathways of epichlorohydrin and analysis of the C-C bond fission channels from an O(3P)+allyl radical intermediate  

NASA Astrophysics Data System (ADS)

This study initially characterizes the primary photodissociation processes of epichlorohydrin, c-(H2COCH)CH2Cl. The three dominant photoproduct channels analyzed are c-(H2COCH)CH2+Cl, c-(H2COCH)+CH2Cl, and C3H4O+HCl. In the second channel, the c-(H2COCH) photofission product is a higher energy intermediate on C2H3O global potential energy surface and has a small isomerization barrier to vinoxy. The resulting highly vibrationally excited vinoxy radicals likely dissociate to give the observed signal at the mass corresponding to ketene, H2CCO. The final primary photodissociation pathway HCl+C3H4O evidences a recoil kinetic energy distribution similar to that of four-center HCl elimination in chlorinated alkenes, so is assigned to production of c-(H2COC)=CH2; the epoxide product is formed with enough vibrational energy to isomerize to acrolein and dissociate. The paper then analyzes the dynamics of the C3H5O radical produced from C-Cl bond photofission. When the epoxide radical photoproduct undergoes facile ring opening, it is the radical intermediate formed in the O(3P)+allyl bimolecular reaction when the O atom adds to an end C atom. We focus on the HCO+C2H4 and H2CO+C2H3 product channels from this radical intermediate in this report. Analysis of the velocity distribution of the momentum-matched signals from the HCO+C2H4 products at m/e=29 and 28 shows that the dissociation of the radical intermediate imparts a high relative kinetic energy, peaking near 20 kcal/mol, between the products. Similarly, the energy imparted to relative kinetic energy in the H2CO+C2H3 product channel of the O(3P)+allyl radical intermediate also peaks at high-recoil kinetic energies, near 18 kcal/mol. The strongly forward-backward peaked angular distributions and the high kinetic energy release result from tangential recoil during the dissociation of highly rotationally excited nascent radicals formed photolytically in this experiment. The data also reveal substantial branching to an HCCH+H3CO product channel. We present a detailed statistical prediction for the dissociation of the radical intermediate on the C3H5O potential energy surface calculated with coupled cluster theory, accounting for the rotational and vibrational energy imparted to the radical intermediate and the resulting competition between the H+acrolein, HCO+C2H4, and H2CO+C2H3 product channels. We compare the results of the theoretical prediction with our measured branching ratios. We also report photoionization efficiency (PIE) curves extending from 9.25 to 12.75 eV for the signal from the HCO+C2H4 and H2CO+C2H3 product channels. Using the C2H4 bandwidth-averaged absolute photoionization cross section at 11.27 eV and our measured relative photoion signals of C2H4 and HCO yields a value of 11.6+1/-3 Mb for the photoionization cross section of HCO at 11.27 eV. This determination puts the PIE curve of HCO measured here on an absolute scale, allowing us to report the absolute photoionization efficiency of HCO over the entire range of photoionization energies.

Fitzpatrick, Benjamin L.; Alligood, Bridget W.; Butler, Laurie J.; Lee, Shih-Huang; Lin, Jim-Min, Jr.

2010-09-01

93

A calculation of the diffusion energies for adatoms on surfaces of F.C.C. metals  

NASA Technical Reports Server (NTRS)

The activation energies for diffusion were determined for gold, platinum and iridium adatoms on plane and plane PT surfaces and were found to be in good agreement with the measurements reported by Bassett and Webber. The Lennard-Jones pair potentials were used to model the interatomic forces, and relaxation of the substrate atoms in near proximity to the adatom was considered in detail. The present calculations clarify the mechanism of the observed two-dimensional diffusion of platinum and iridium atoms on a plane PT surface. The results are compared with those obtained using Morse potential functions and different relaxation techniques.

Halicioglu, T.; Pound, G. M.

1979-01-01

94

The Bond Dissociation Energies of 1-Butene  

NASA Technical Reports Server (NTRS)

The bond dissociation energies of 1-butene and several calibration systems are computed using the G2(MP2) approach. The agreement between the calibration systems and experiment is very good. The computed values for 1-butene are compared with calibration systems and the agreement between the computed results for 1-butene and the "rule of thumb" values from the smaller systems is remarkably good.

Bauschlicher, Charles W., Jr.; Langhoff, Stephen R. (Technical Monitor)

1994-01-01

95

Thermochemistry and bond dissociation energies of ketones.  

PubMed

Ketones are a major class of organic chemicals and solvents, which contribute to hydrocarbon sources in the atmosphere, and are important intermediates in the oxidation and combustion of hydrocarbons and biofuels. Their stability, thermochemical properties, and chemical kinetics are important to understanding their reaction paths and their role as intermediates in combustion processes and in atmospheric chemistry. In this study, enthalpies (?H°(f 298)), entropies (S°(T)), heat capacities (C(p)°(T)), and internal rotor potentials are reported for 2-butanone, 3-pentanone, 2-pentanone, 3-methyl-2-butanone, and 2-methyl-3-pentanone, and their radicals corresponding to loss of hydrogen atoms. A detailed evaluation of the carbon-hydrogen bond dissociation energies (C-H BDEs) is also performed for the parent ketones for the first time. Standard enthalpies of formation and bond energies are calculated at the B3LYP/6-31G(d,p), B3LYP/6-311G(2d,2p), CBS-QB3, and G3MP2B3 levels of theory using isodesmic reactions to minimize calculation errors. Structures, moments of inertia, vibrational frequencies, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) density functional level and are used to determine the entropies and heat capacities. The recommended ideal gas-phase ?H°(f 298), from the average of the CBS-QB3 and G3MP2B3 levels of theory, as well as the calculated values for entropy and heat capacity are shown to compare well with the available experimental data for the parent ketones. Bond energies for primary, secondary, and tertiary radicals are determined; here, we find the C-H BDEs on carbons in the ? position to the ketone group decrease significantly with increasing substitution on these ? carbons. Group additivity and hydrogen-bond increment values for these ketone radicals are also determined. PMID:22668341

Hudzik, Jason M; Bozzelli, Joseph W

2012-06-14

96

The binding energy and bonding in dialane.  

PubMed

The binding energy of dialane, Al2H6, has been measured using mass spectrometric techniques to be 33 +/- 5 kcal/mol. This represents the first measurement of the thermochemical properties of dialane, which has only recently been observed in low-temperature matricies. High-level quantum mechanical calculations give a binding energy in agreement with the measured value. Experimental and quantum mechanical calculations show that dialane is chemically similar to diborane, B2H6, even though the bonding for these two systems shows significant differences. PMID:16104745

Goebbert, Daniel J; Hernandez, Heriberto; Francisco, Joseph S; Wenthold, Paul G

2005-08-24

97

Hydrogenolysis and homologation of linear and branched pentenes on Ru/SiO/sub 2/ catalysts: implication in the mechanism of C-C bond formation and cleavage on metal surfaces  

SciTech Connect

Hydrogenolysis and homologation of 1-pentene to butenes and hexenes take place simultaneously and at the same rate over a Ru/SiO/sub 2/ catalysts at 110/sup 0/C, suggesting that these two reactions are mechanistically related. /sup 13/C labeling experiments indicate that C-C cleavage occurs at the double bond of 1-pentene-1-/sup 13/C leading to unlabeled 1-butene and labeled hexenes. The product distribution in the hydrogenolysis of 1-pentene, 2-pentenes, 3-methyl-1-butene, 2-methyl-2-butene, and 2-methyl-1-butene is accounted for by a carbene-olefin mechanism, which can therefore be considered as a reasonable common path for the formation and cleavage of carbon-carbon bonds on metal surfaces.

Rodriguez, E.; Leconte, M.; Basset, J.M.; Tanaka, K.; Tanaka, K.I.

1988-01-06

98

CeCl3·7H2O catalyzed C-C and C-N bond-forming cascade cyclization with subsequent side-chain functionalization and rearrangement: a domino approach to pentasubstituted pyrrole analogues.  

PubMed

CeCl(3)·7H(2)O is found as an efficient catalyst for new intermolecular domino reactions of three-, four- and seven-component assemblies of common precursors under benign reaction conditions. Generation of enaminioesters from ?-keto esters and primary amines, activation of their allylic sp(3) C-H, vinylic sp(2) C-H and N-H bonds, multi C-C and C-N bond-forming cascade cyclization with 1,2-diketones and subsequent side-chain alkylation have been developed to construct functionalized pentasubstituted pyrroles and their chiral analogues. The scope of the domino reaction is successfully explored toward synthesis of highly aryl-substituted pyrroles, pentasubstituted pyrroles bearing C2-olefinic side-chain and spiro-2-pyrrolinones and their chiral analogues via unusual side-chain amination, elimination and ring contraction. The new domino reaction is operationally simple, robust, substrate specific, selective and high yielding. PMID:23113545

Dhara, Dipankar; Gayen, Krishnanka S; Khamarui, Saikat; Pandit, Palash; Ghosh, Sukla; Maiti, Dilip K

2012-11-16

99

Synthesis of (±)-aphanorphine: a new approach to tricyclic 3-benzazepine scaffold using two radical C–C bond-forming reactions  

Microsoft Academic Search

An expeditious approach to (±)-aphanorphine has been established using readily available starting materials. The present synthesis relies on the direct assembly between N-methylpyrrolidone (NMP) and 2-bromoanisaldehyde, which takes place through Et3B\\/air-mediated transformation of the ?-nitrogen-substituted sp3C–H bond, and features a new design concept for the synthesis of the tricyclic 3-benzazepine skeleton.

Takehiko Yoshimitsu; Chie Atsumi; Emiko Iimori; Hiroto Nagaoka; Tetsuaki Tanaka

2008-01-01

100

Bond resonance energy and verification of the isolated pentagon rule  

Microsoft Academic Search

The isolated pentagon rule (IPR) states that fullerenes with isolated pentagons are kinetically much more stable than their fused pentagon counterparts. This rule can be verified in terms of a graph-theoretically defined bond resonance energy. In general, a Ï bond shared by two pentagons has a large negative bond resonance energy, thus contributing significantly to the increase in kinetic instability

Jun-ichi Aihara; Jun Ichi

1995-01-01

101

Synthetic Approaches to (smif)2Ti (smif = 1,3-di-(2-pyridyl)-2-azaallyl) Reveal Redox Non-Innocence and C-C Bond-Formation  

PubMed Central

Attempted syntheses of (smif)2Ti (smif = 1,3-di-(2-pyridyl)-2-azaallyl) based on metatheses of TiClnLm (n = 2–4) with M(smif) (M = Li, Na), in the presence of a reducing agent (Na/Hg) when necessary, failed, but several apparent Ti(II) species were identified by X-ray crystallography and multidimensional NMR spectroscopy: (smif){Li(smif-smif)}Ti (1, X-ray), [(smif)Ti]2(?-?3,?3-N,N(py)2-smif,smif) (2), (smif)Ti(?3-N,N(py)2-smif,(smif)H) (3), and (smif)Ti(dpma) (4). NMR spectroscopy and K-edge XAS showed that each compound possesses ligands that are redox non-innnocent, such that d1 Ti(III) centers AF-couple to ligand radicals: (smif){Li(smif-smif)2?}TiIII (1), [(smif2?)TiIII]2(?-?3,?3-N,N(py)2-smif,smif) (2), [(smif2?)TiIII](?3-N,N(py)2-smif,(smif)H) (3), and (smif2?)TiIII(dpma) (4). The instability of the (smif)2Ti relative to its C-C coupled dimer, 2, is rationalized via the complementary nature of the amide and smif radical anion ligands, which are also common to 3 and 4. Calculations support this contention.

Frazier, Brenda A.; Wolczanski, Peter T.; Keresztes, Ivan; DeBeer, Serena; Lobkovsky, Emil B.; Pierpont, Aaron W.; Cundari, Thomas R.

2012-01-01

102

Ether complexes of tungsten with two different binding modes: An O-bound ether and an {eta}{sup 2}-(C=C) vinyl ether. Evidence for C-H...O hydrogen bonding of vinylic C-H groups  

SciTech Connect

The reaction of PhCH(OCH{sup 3}){sup 2} with Cp(CO){sup 3}WH and HOTf gives [Cp(CO){sup 3}W(PhCH{sup 2}OCH{sup 3})]{sup +}OTf{sup -}. The structure of this benzyl methyl ether complex was determined by single crystal X-ray diffraction and was shown to have the ether bonded to tungsten through the oxygen. This compound was isolated as a kinetic product of the reaction; it decomposes in solution by releasing free PhCH{sup 2}OCH{sup 3} and forming Cp(CO){sup 3}WOTf. An analog with the BAr`{sup 4}{sup -} counterion [Ar` = 3, 5-bis(trifluoromethyl)phenyl] is more stable. The reaction of the vinyl acetal CH{sup 2}=CHCH(OEt){sup 2} with Cp(CO){sup 3}WH and HOTf produces [Cp(CO){sup 3}W({eta}{sup 2}-EtOCH=CHCH{sup 3})]{sup +} OTf{sup -}, in which the ether is bonded to tungsten through the C=C bond of the vinyl ether. The crystal structure of this compound shows that the W-C(OEt) distance (2.69(3) A) is significantly longer than the W-C(CH{sup 3}) distance (2.37(3) A). There are weak C-H...O hydrogen bonds between both vinyl CH`s and oxygens of the triflate counterions. Evidence is presented that some of these weak hydrogen bonds are maintained in CD{sup 2}Cl{sup 2} solution but not in CD{sup 3}CN. 44 refs., 4 figs., 3 tabs.

Song, J.S.; Szalda, D.J.; Bullock, R.M. [Brookhaven National Lab., Upton, NY (United States)] [Brookhaven National Lab., Upton, NY (United States)

1996-11-13

103

Middle School Chemistry: Energy Levels, Electrons, and Covalent Bonding  

NSDL National Science Digital Library

This multimedia lesson for Grades 7-8 features eight animations and a hands-on lab to explore the role of valence electrons in covalent bonding. The multimedia approach provides an opportunity to visualize the attractions between atoms that result in covalent bonds. The lab investigation uses a 9-volt battery, alligator clips, and pencils to show how electrical energy can break the covalent bonds in water molecules. Editor's Note: Covalent bonding occurs when electrons are shared between atoms; ionic bonding occurs when electrons are transferred between atoms. The processes are quite different. This module very effectively explores both formation and breaking of covalent bonds. Allow two class periods.

Galvan, Patti; Kessler, Jim

2011-08-17

104

Strong Lewis acid air-stable cationic titanocene perfluoroalkyl(aryl)sulfonate complexes as highly efficient and recyclable catalysts for C-C bond forming reactions.  

PubMed

A series of strong Lewis acid air-stable titanocene perfluoroalkyl(aryl)sulfonate complexes Cp2Ti(OH2)2(OSO2X)2·THF (X = C8F17, 1·THF; X = C4F9, 2·H2O·THF; X = C6F5, 3) were successfully synthesized by the treatment of Cp2TiCl2 with C8F17SO3Ag, C4F9SO3Ag and C6F5SO3Ag, respectively. In contrast to well-known titanocene bis(triflate), these complexes showed no change in open air over three months. TG-DSC analysis showed that 1·THF, 2·H2O·THF and 3 were thermally stable at 230 °C, 220 °C and 280 °C, respectively. Conductivity measurements showed that these complexes underwent ionic dissociation in CH3CN solution. X-ray analysis results confirmed that 2·H2O·THF and 3 were cationic. ESR spectra showed that the Lewis acidity of 1·THF (1.06 eV) was higher than that of Sc(3+) (1.00 eV) and Y(3+) (0.85 eV). UV/Vis spectra showed a significant red shift due to the strong complex formation between 10-methylacridone and 2·H2O·THF. Fluorescence spectra showed that the Lewis acidity of 2 (?em = 477 nm) was higher than that of Sc(3+) (?em = 474 nm). These complexes showed high catalytic ability in various carbon-carbon bond forming reactions. Moreover, they show good reusability. Compared with 1·THF, 2·H2O·THF and 3 exhibit higher solubility and better catalytic activity, and will find broad applications in organic synthesis. PMID:24950799

Li, Ningbo; Wang, Jinying; Zhang, Xiaohong; Qiu, Renhua; Wang, Xie; Chen, Jinyang; Yin, Shuang-Feng; Xu, Xinhua

2014-08-14

105

A Tungsten Complex with a Bidentate, Hemilabile N-Heterocyclic Carbene Ligand, Facile Displacement of the Weakly Bound W-(C=C) Bond, and the Vulnerability of the NHC Ligand Toward Catalyst Deactivation During Ketone Hydrogenation  

SciTech Connect

The initial reaction observed between N-heterocyclic carbene IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO)2(PPh3)H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMes)H]+[CpM(CO)2(PPh3)]– . At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO)2(PR3)H (M = Mo, W; R = Me, Ph) produces CpM(CO)2(IMes)H. Hydride transfer from CpW(CO)2(IMes)H to Ph3C+B(C6F5)4- gives CpW(CO)2(IMes)+B(C6F5)4- which was crystallographically characterized using x-ray radiation from a synchrotron. The IMes is bonded as a bidentate ligand, through the carbon of the carbene as well as forming a weak bond from the metal to a C=C bond of one mesityl ring. The weakly bound C=C ligand is hemilabile, being readily displaced by H2, THF, ketones or alcohols. Reaction of CpW(CO)2(IMes)+ with H2 gives the dihydride complex [CpW(CO)2(IMes)(H)2]+. Addition of Et2CH–OH to CpW(CO)2(IMes)+B(C6F5)4- gives the alcohol complex [CpM(CO)2(IMes)(Et2CH–OH)]+[B(C6F5)4]– which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OH group. Addition of H2 to the ketone complex [CpW(CO)2(IMes)(Et2C=O)]+[B(C6F5)4]– produces an equilibrium with the dihydride [CpW(CO)2(IMes)(H)2]+ (Keq = 1.1 ? 103 at 25 °C). The tungsten ketone complex [CpW(CO)2(IMes)(Et2C=O)]+[B(C6F5)4]– serves as a modest catalyst for hydrogenation of Et2C=O to Et2CH–OH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]+B(C6F5)4-, indicating that these catalysts with N-heterocyclic carbenes ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.

Wu, Fan; Dioumaev, Vladimir K.; Szalda, David J.; Hanson, Jonathan; Bullock, R. Morris

2007-09-24

106

Isomerization around C-C and C-O bonds in 1-propanol: Collisional relaxation in supersonic jets and selective IR photo-isomerization in cryogenic matrices  

NASA Astrophysics Data System (ADS)

The conformational equilibria and isomerization processes of 1-propanol are analyzed by vibrational spectroscopy at low temperatures. Supersonic jet experiments provide constraints on the energy sequence. All five distinguishable monomer conformers are assigned in the OH stretching region. Collisional relaxation affects the OH group conformation (gauche or trans, g/t), but the barriers to alkyl chain isomerization (G/T) prevent relaxation of the latter. Alkyl chain isomerization can be induced in rare gas and nitrogen cryogenic matrices by suitable monochromatic irradiation. Selective excitation of the OH stretch of the Gt isomer transfers the alkyl chain from G to T. In N2 matrices, reversible OH group isomerization between Tt and Tg can also be induced by selective irradiation, whereas in solid CCl4 matrices, only Gt ? Gg OH group isomerization is observed. The competition between intramolecular and intermolecular energy transfer and the matrix-dopant interaction determines the torsional subspace dynamics of the vibrationally excited propanol molecules.

Wassermann, Tobias N.; Suhm, Martin A.; Roubin, Pascale; Coussan, Stéphane

2012-10-01

107

Municipal bond financing of solar energy facilities  

Microsoft Academic Search

The application of the laws of municipal bond financing to solar facilities is examined. The type of facilities under consideration are outlined. The general legal principles of municipal securities financing are discussed. The effect of recent decisions applying antitrust liability to municipal corporations is also discussed. Five specific types of municipal bonds are explained. The application of Section 103 of

1979-01-01

108

Bonding  

NSDL National Science Digital Library

Bonding Purpose: To review the 3 Types of Bonds and the 4 Intermolecular Forces. Assignment: Answer the following questions on a separate piece of paper: 1) List the 3 types of bonding, give descriptions and one example of each 2) List the 4 intermolecular forces and draw examples of each. Be ...

Cutting, Mrs.

2008-03-08

109

Do Bond Functions Help for the Calculation of Accurate Bond Energies?  

NASA Technical Reports Server (NTRS)

The bond energies of 8 chemically bound diatomics are computed using several basis sets with and without bond functions (BF). The bond energies obtained using the aug-pVnZ+BF basis sets (with a correction for basis set superposition error, BSSE) tend to be slightly smaller that the results obtained using the aug-pV(n+I)Z basis sets, but slightly larger than the BSSE corrected aug-pV(n+I)Z results. The aug-cc-pVDZ+BF and aug-cc-pVTZ+BF basis sets yield reasonable estimates of bond energies, but, in most cases, these results cannot be considered highly accurate. Extrapolation of the results obtained with basis sets including bond functions appears to be inferior to the results obtained by extrapolation using atom-centered basis sets. Therefore bond functions do not appear to offer a path for obtaining highly accurate results for chemically bound systems at a lower computational cost than atom centered basis sets.

Bauschlicher, Charles W., Jr.; Arnold, James (Technical Monitor)

1998-01-01

110

A Tungsten Complex with a Bidentate, Hemilabile N-Heterocyclic Carbene Ligand, Facile Displacement of the Weakly Bound W-(C=C) Bond, and the Vulnerability of the NHC Ligand Towards Catalyst Deactivation During Ketone Hydrogenation  

SciTech Connect

The initial reaction observed between the N-heterocyclic carbene IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO){sub 2}(PPh{sub 3})H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMes)H]{sup +}[CpM(CO){sub 2}(PPh{sub 3})]{sup -}. At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO){sub 2}(PR{sub 3})H (M = Mo, W; R = Me, Ph) produces CpM(CO){sub 2}(IMes)H. Hydride transfer from CpW(CO)2(IMes)H to Ph{sub 3}C{sub +}B(C{sub 6}F{sub 5}){sub 4}{sup -} gives CpW(CO){sub 2}(IMes){sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -}, which was crystallographically characterized using X-ray radiation from a synchrotron. The IMes is bonded as a bidentate ligand, through the carbon of the carbene as well as forming a weak bond from the metal to a C=C bond of one mesityl ring. The weakly bound C=C ligand is hemilabile, being readily displaced by H{sub 2}, THF, ketones, or alcohols. Reaction of CpW(CO){sub 2}(IMes){sup +} with H{sub 2} gives the dihydride complex [CpW(CO){sub 2}(IMes)(H){sub 2}]{sup +}. Addition of Et{sub 2}CH-OH to CpW(CO){sub 2}(IMes){sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -} gives the alcohol complex [CpW(CO){sub 2}(IMes)(Et{sub 2}CH-OH)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -}, which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OH group. Addition of H{sub 2} to the ketone complex [CpW(CO){sub 2}(IMes)(Et{sub 2}C=O)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -} produces an equilibrium with the dihydride [CpW(CO){sub 2}(IMes)(H){sub 2}]{sup +} (K{sub eq} = 1.1 x 10{sup 3} at 25 {sup o}C). The tungsten ketone complex [CpW(CO){sub 2}(IMes)(Et{sub 2}C=O)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -}- serves as a modest catalyst for hydrogenation of Et{sub 2}C=O to Et{sub 2}CH-OH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]{sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -}, indicating that these catalysts with N-heterocyclic carbene ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.

Wu,F.; Dioumaev, V.; Szalda, D.; Hanson, J.; Bullock, R.

2007-01-01

111

Relativistic contributions to ionization energies and bond lengths  

Microsoft Academic Search

The interchange theorem of double perturbation theory permits two equivalent approaches for the determination and discussion of relativistic changes of ionization energies and bond lengths. Electron density differences due to ionization and bond length variation, respectively, at the nonrelativistic level, or alternatively density differences due to relativity, have to be taken into account ; either may be used for explaining

W. H. E. Schwarz; S. Y. Chu; F. Mark

1983-01-01

112

The Calculation of Accurate Metal-Ligand Bond Energies  

NASA Technical Reports Server (NTRS)

The optimization of the geometry and calculation of zero-point energies are carried out at the B3LYP level of theory. The bond energies are determined at this level, as well as at the CCSD(T) level using very large basis sets. The successive OH bond energies to the first row transition metal cations are reported. For most systems there has been an experimental determination of the first OH. In general, the CCSD(T) values are in good agreement with experiment. The bonding changes from mostly covalent for the early metals to mostly electrostatic for the late transition metal systems.

Bauschlicher, Charles W.; Partridge, Harry, III; Ricca, Alessandra; Arnold, James O. (Technical Monitor)

1997-01-01

113

Nonaqueous and halide-free route to crystalline BaTiO3, SrTiO3, and (Ba,Sr)TiO3 nanoparticles via a mechanism involving C-C bond formation.  

PubMed

A novel nonaqueous route for the preparation of nanocrystalline BaTiO(3), SrTiO(3), and (Ba,Sr)TiO(3) has been developed. In a simple one-pot reaction process, the elemental alkaline earth metals are directly dissolved in benzyl alcohol at slightly elevated temperatures. After the addition of Ti(O(i)Pr)(4), the reaction mixture is heated to 200 degrees C, resulting in the formation of a white precipitate. XRD measurements prove the exclusive presence of the perovskite phase without any other crystalline byproducts such as BaCO(3) or TiO(2). TEM investigations reveal that the BaTiO(3) nanoparticles are nearly spherical in shape with diameters ranging from 4 to 5 nm. The SrTiO(3) particles display less uniform particle shapes, and the size varies between 5 and 10 nm. Lattice fringes observed in HRTEM measurements further prove the high crystallinity of the nanoparticles. Surprisingly, GC-MS analysis of the reaction solution after hydrothermal treatment shows that hardly any ether formation occurs during the BaTiO(3) synthesis. Instead, the presence of 4-phenyl-2-butanol in stoichiometric amounts gives evidence that the formation mechanism proceeds mainly via a novel pathway involving C-C bond formation between benzyl alcohol and the isopropanolate ligand. PMID:15264847

Niederberger, Markus; Garnweitner, Georg; Pinna, Nicola; Antonietti, Markus

2004-07-28

114

Direct-dynamics VTST study of hydrogen or deuterium abstraction and C-C bond formation or dissociation in the reactions of CH3 + CH4, CH3 + CD4, CH3D + CD3, CH3CH3 + H, and CH3CD3 + D  

NASA Astrophysics Data System (ADS)

Direct-dynamics variational transition-state theory calculations are studied at the MPWB1K/6-311++G(d,p) level for the four parts of reactions. The first part is hydrogen or deuterium abstraction in the reactions of CH3 + CH4, CH3 + CD4, and CH3D + CH3. The second part involves C-C bond formation in these reactions. The third one is the reactions of CH3CH3 + H and CH3CD3 + D to form of H2, HD, and D2. The last one is the dissociation of C-C bonds in the last group of reactions. The ground-state vibrational adiabatic potential is plotted for all channels. We have carried out direct-dynamics calculations of the rate constants, including multidimensional tunneling in the temperature range T = 200-2200 K. The results of CVT/?OMT rate constants were in good agreement with the experimental data which were available for some reactions. Small-curvature tunneling and Large-curvature tunneling with the LCG4 version were used to include the quantum effects in calculation of the rate constants. To try to find the region of formation and dissociation of bounds we have also reported the variations of harmonic vibrational frequencies along the reaction path. The thermally averaged transmission probability (P(E)exp (-?E/RT)) and representative tunneling energy at 298 K are reported for the reactions in which tunneling is important. We have calculated kinetic isotope effect which shows tunneling and vibrational contributions are noticeable to determine the rate constant. Nonlinear least-squares fitting is used to calculate rate constant expressions in the temperature range 200-2200 K. These expressions revealed that pre-exponential factor includes two parts; the first part is a constant number which is important at low temperatures while the second part is temperature dependent which is significant at high temperatures.

Ramazani, Shapour

2013-05-01

115

How resonance assists hydrogen bonding interactions: an energy decomposition analysis.  

PubMed

Block-localized wave function (BLW) method, which is a variant of the ab initio valence bond (VB) theory, was employed to explore the nature of resonance-assisted hydrogen bonds (RAHBs) and to investigate the mechanism of synergistic interplay between pi delocalization and hydrogen-bonding interactions. We examined the dimers of formic acid, formamide, 4-pyrimidinone, 2-pyridinone, 2-hydroxpyridine, and 2-hydroxycyclopenta-2,4-dien-1-one. In addition, we studied the interactions in beta-diketone enols with a simplified model, namely the hydrogen bonds of 3-hydroxypropenal with both ethenol and formaldehyde. The intermolecular interaction energies, either with or without the involvement of pi resonance, were decomposed into the Hitler-London energy (DeltaEHL), polarization energy (DeltaEpol), charge transfer energy (DeltaECT), and electron correlation energy (DeltaEcor) terms. This allows for the examination of the character of hydrogen bonds and the impact of pi conjugation on hydrogen bonding interactions. Although it has been proposed that resonance-assisted hydrogen bonds are accompanied with an increasing of covalency character, our analyses showed that the enhanced interactions mostly originate from the classical dipole-dipole (i.e., electrostatic) attraction, as resonance redistributes the electron density and increases the dipole moments in monomers. The covalency of hydrogen bonds, however, changes very little. This disputes the belief that RAHB is primarily covalent in nature. Accordingly, we recommend the term "resonance-assisted binding (RAB)" instead of "resonance-assisted hydrogen bonding (RHAB)" to highlight the electrostatic, which is a long-range effect, rather than the electron transfer nature of the enhanced stabilization in RAHBs. PMID:17143867

Beck, John Frederick; Mo, Yirong

2007-01-15

116

C-C bond unsaturation degree in monosubstituted ferrocenes for molecular electronics investigated by a combined near-edge x-ray absorption fine structure, x-ray photoemission spectroscopy, and density functional theory approach  

NASA Astrophysics Data System (ADS)

We present the results of an experimental and theoretical investigation of monosubstituted ethyl-, vinyl-, and ethynyl-ferrocene (EtFC, VFC, and EFC) free molecules, obtained by means of synchrotron-radiation based C 1s photoabsorption (NEXAFS) and photoemission (C 1s XPS) spectroscopies, and density functional theory (DFT) calculations. Such a combined study is aimed at elucidating the role played by the C-C bond unsaturation degree of the substituent on the electronic structure of the ferrocene derivatives. Such substituents are required for molecular chemical anchoring onto relevant surfaces when ferrocenes are used for molecular electronics hybrid devices. The high resolution C 1s NEXAFS spectra exhibit distinctive features that depend on the degree of unsaturation of the hydrocarbon substituent. The theoretical approach to consider the NEXAFS spectrum made of three parts allowed to disentangle the specific contribution of the substituent group to the experimental spectrum as a function of its unsaturation degree. C 1s IEs were derived from the experimental data analysis based on the DFT calculated IE values for the different carbon atoms of the substituent and cyclopentadienyl (Cp) rings. Distinctive trends of chemical shifts were observed for the substituent carbon atoms and the substituted atom of the Cp ring along the series of ferrocenes. The calculated IE pattern was rationalized in terms of initial and final state effects influencing the IE value, with special regard to the different mechanism of electron conjugation between the Cp ring and the substituent, namely the ?/? hyperconjugation in EtFC and the ?-conjugation in VFC and EFC.

Boccia, A.; Lanzilotto, V.; Marrani, A. G.; Stranges, S.; Zanoni, R.; Alagia, M.; Fronzoni, G.; Decleva, P.

2012-04-01

117

Bond energy decomposition analysis for subsystem density functional theory.  

PubMed

We employed an explicit expression for the dispersion (D) energy in conjunction with Kohn-Sham (KS) density functional theory and frozen-density embedding (FDE) to calculate interaction energies between DNA base pairs and a selected set of amino acid pairs in the hydrophobic core of a small protein Rubredoxin. We use this data to assess the accuracy of an FDE-D approach for the calculation of intermolecular interactions. To better analyze the calculated interaction energies we furthermore propose a new energy decomposition scheme that is similar to the well-known KS bond formation analysis [F. M. Bickelhaupt and E. J. Baerends, Rev. Comput. Chem. 15, 1 (2000)], but differs in the electron densities used to define the bond energy. The individual subsystem electron densities of the FDE approach sum to the total electron density which makes it possible to define bond energies in terms of promotion energies and an explicit interaction energy. We show that for the systems considered only a few freeze-and-thaw cycles suffice to reach convergence in these individual bond energy components, illustrating the potential of FDE-D as an efficient method to calculate intermolecular interactions. PMID:23485283

Beyhan, S Maya; Götz, Andreas W; Visscher, Lucas

2013-03-01

118

Covalent bonding: the fundamental role of the kinetic energy.  

PubMed

This work addresses the continuing disagreement between two prevalent schools of thought concerning the mechanism of covalent bonding. According to Hellmann, Ruedenberg, and Kutzelnigg, a lowering of the kinetic energy associated with electron delocalization is the key stabilization mechanism. The opposing view of Slater, Feynman, and Bader has maintained that the source of stabilization is electrostatic potential energy lowering due to electron density redistribution to binding regions between nuclei. Despite the large body of accurate quantum chemical work on a range of molecules, the debate concerning the origin of bonding continues unabated, even for H2(+), the simplest of covalently bound molecules. We therefore present here a detailed study of H2(+), including its formation, that uses a sequence of computational methods designed to reveal the relevant contributing mechanisms as well as the spatial density distributions of the kinetic and potential energy contributions. We find that the electrostatic mechanism fails to provide real insight or explanation of bonding, while the kinetic energy mechanism is sound and accurate but complex or even paradoxical to those preferring the apparent simplicity of the electrostatic model. We further argue that the underlying mechanism of bonding is in fact of dynamical character, and analyses that focus on energy do not reveal the origin of covalent bonding in full clarity. PMID:23859401

Bacskay, George B; Nordholm, Sture

2013-08-22

119

Electronic effect in C-H and C-C bond activation: state-specific reactions of Fe/sup +/(/sup 6/D, /sup 4/F) with methane, ethane, and propane  

SciTech Connect

Reactions of atomic iron ions with methane, ethane, and propane are studied with guided ion beam mass spectrometry. By using different ion sources different electronic states of the ion can be prepared and studied in detail. The first excited state, Fe/sup +/(/sup 4/F), is more reactive than the ground state, Fe/sup +/(/sup 6/D), for all endothermic reactions in all three systems. This result is similar to recent observations of the reactions of these states with H/sub 2/. The different reactivities are explained by using simple molecular orbital arguments. In contrast, Fe/sup +/(/sup 4/F) reacts less efficiently than Fe/sup +/(/sup 6/D) in the exothermic reactions of ethane and propane below 0.5 eV but more efficiently at higher energies. This behavior is explained by a potential energy surface crossing that is avoided at low kinetic energies due to spin-orbit interactions and is permitted at higher energies. Finally, analysis of the threshold behavior of the endothermic reactions provides the bond dissociation energies, D/sup 0/(Fe/sup +/-CH/sub 3/) = 2.51 +/- 0.10 eV (57.9 +/- 2.4 kcal/mol) and D/sup 0/(FeH) = 1.98 +/- 0.13 eV (45.7 +/- 3.0 kcal/mol).

Schultz, R.H.; Elkind, J.L.; Armentrout, P.B.

1988-01-20

120

Hydrogen bond energy of the water dimer  

SciTech Connect

Large scale ab initio molecular orbital calculations on the binding energy of the water dimer have been performed. These calculations extend the previous correlation consistent basis set work to include larger basis sets (up to 574 functions), and core/valence correlation effects have now been included. The present work confirms the earlier estimate of -4.9 kcal/mol as the MP2(FC) basis set limit. Core/valence correlation effects are found to increase the binding energy by nearly 0.05 kcal/mol. The best estimate of the electronic binding energy of the water dimer is -5.0{+-}0.1 kcal/mol. Correcting this value for zero-point and temperature effects yields the value {Delta}H(375)=-3.2{+-}0.1 kcal/mol. This value is within the error limits of the best experimental estimate of -3.6{+-}0.5 kcal/mol with the calculations favoring the lower end of the experimental energy range. It should be useful to adopt the present estimate in empirical and semiempirical model potentials. 39 refs., 1 fig., 3 tabs.

Feyereisen, M.W. [Cray Research, Inc., Eagen, MN (United States)] [Cray Research, Inc., Eagen, MN (United States); Feller, D. [Pacific Northwest Lab., Richland, WA (United States)] [Pacific Northwest Lab., Richland, WA (United States); Dixon, D.A. [Du Pont Central Research and Development, Wilmington, DE (United States)] [Du Pont Central Research and Development, Wilmington, DE (United States)

1996-02-22

121

Storing Renewable Energy in Chemical Bonds  

SciTech Connect

With nearly 7 billion people, the world's population is demanding more electricity every year. Improved technologies are bringing wind and solar power to our electrical grid. However, wind turbines and solar panels only work when the wind blows or the sun shines. PNNL scientists discuss catalysis approaches for storing and releasing energy on demand.

Helm, Monte; Bullock, Morris

2013-03-27

122

Storing Renewable Energy in Chemical Bonds  

ScienceCinema

With nearly 7 billion people, the world's population is demanding more electricity every year. Improved technologies are bringing wind and solar power to our electrical grid. However, wind turbines and solar panels only work when the wind blows or the sun shines. PNNL scientists discuss catalysis approaches for storing and releasing energy on demand.

Helm, Monte; Bullock, Morris

2014-06-13

123

Ion beam studies of the reactions of atomic cobalt ions with alkanes: determination of metal-hydrogen and metal-carbon bond energies and an examination of the mechanism by which transition metals cleave carbon-carbon bonds  

SciTech Connect

An ion beam apparatus is employed to study the reactions of singly charged cobalt positive ions with hydrogen and 17 alkanes. Reaction cross sections and product distributions as a function of kinetic energy are determined. Exothermic carbon-carbon bond cleavage reactions are observed for all alkanes but methane and ethane. A mechanism involving oxidative addition of C-C and C-H bonds to cobalt as a first step is demonstrated to account for all major reactions at all energies. Interpretation of several endothermic processes allows the extraction of thermochemical data. The bond dissociation energies obtained are D/sup 0/(Co/sup +/-H) = 52 +- 4 kcal/mol, D/sup 0/(Co-H) = 39 +- 6 kcal/mol, D/sup 0/(Co/sup +/-CH/sub 3/) = 61 +- 4 kcal/mol, and D/sup 0/(Co-CH/sub 3/) = 41 +- 10 kcal/mol.

Armentrout, P.B.; Beauchamp, J.L.

1981-02-25

124

Students' interdisciplinary reasoning about "high-energy bonds" and ATP  

NASA Astrophysics Data System (ADS)

Students' sometimes contradictory ideas about ATP (adenosine triphosphate) and the nature of chemical bonds have been studied in the biology and chemistry education literatures, but these topics are rarely part of the introductory physics curriculum. We present qualitative data from an introductory physics course for undergraduate biology majors that seeks to build greater interdisciplinary coherence and therefore includes these topics. In these data, students grapple with the apparent contradiction between the energy released when the phosphate bond in ATP is broken and the idea that an energy input is required to break a bond. We see that students' perceptions of how each scientific discipline bounds the system of interest can influence how they justify their reasoning about a topic that crosses disciplines. This has consequences for a vision of interdisciplinary education that respects disciplinary perspectives while bringing them into interaction in ways that demonstrate consistency amongst the perspectives.

Dreyfus, Benjamin W.; Geller, Benjamin D.; Sawtelle, Vashti; Svoboda, Julia; Turpen, Chandra; Redish, Edward F.

2013-01-01

125

Students' interdisciplinary reasoning about "high-energy bonds" and ATP  

NSDL National Science Digital Library

Students' sometimes contradictory ideas about ATP (adenosine triphosphate) and the nature of chemical bonds have been studied in the biology and chemistry education literatures, but these topics are rarely part of the introductory physics curriculum. We present qualitative data from an introductory physics course for undergraduate biology majors that seeks to build greater interdisciplinary coherence and therefore includes these topics. In these data, students grapple with the apparent contradiction between the energy released when the phosphate bond in ATP is broken and the idea that an energy input is required to break a bond. We see that students' perceptions of how each scientific discipline bounds the system of interest can influence how they justify their reasoning about a topic that crosses disciplines. This has consequences for a vision of interdisciplinary education that respects disciplinary perspectives while bringing them into interaction in ways that demonstrate consistency amongst the perspectives

Dreyfus, Benjamin W.; Geller, Benjamin D.; Sawtelle, Vashti; Svoboda, Julia; Turpen, Chandra; Redish, Edward F.

2013-09-07

126

The kinetic energy change on covalent bond formation  

PubMed Central

Stimulated by an analysis of the classical molecular orbital and valence bond descriptions of the two-electron normal covalent bond (both faulty), the argument is made that there exist good representations of the kinetic energy change ?T, on nonpolar covalent bond formation in a diatomic molecule, of the form ?T(R) = ?F(R - r?)S(r?)dr?. Here F is a nonlinear response function which itself involves the overlap S. The kinetic change is known to satisfy the sum rule ?0??T(R)dR = Z?Z? exactly; it is shown how this can be built into the treatment by the use of Fourier transform methods. Also considered is ?0??T(R)R2dR, which is an important additional property of the kinetic energy change. Representation of ?T(R) as a Morse function, already known to be highly accurate, is shown to exactly conform to the proposed form.

March, Norman H.; Parr, Robert G.; Mucci, Joe F.

1981-01-01

127

Bond Dissociation Energies in Second-Row Compounds  

SciTech Connect

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Heats of formation at 0 and 298 K are predicted for PF?, PF?, PF?O, SF?, SF?, SF?, SF?O, SF?O?, and SF?O as well as a number of radicals derived from these stable compounds on the basis of coupled cluster theory [CCSD(T)] calculations extrapolated to the complete basis set limit. In order to achieve near chemical accuracy (±1 kcal/mol), additional corrections were added to the complete basis set binding energies based on frozen core coupled cluster theory energies: a correction for core-valence effects, a correction for scalar relativistic effects, a correction for first-order atomic spin-orbit effects, and vibrational zero-point energies. The calculated values substantially reduce the error limits for these species. A detailed comparison of adiabatic and diabatic bond dissociation energies (BDEs) is made and used to explain trends in the BDEs. Because the adiabatic BDEs of polyatomic molecules represent not only the energy required for breaking a specific bond but also contain any reorganization energies of the bonds in the resulting products, these BDEs can be quite different for each step in the stepwise loss of ligands in binary compounds. For example, the adiabatic BDE for the removal of one fluorine ligand from the very stable closed-shell SF? molecule to give the unstable SF? radical is 2.8 times the BDE needed for the removal of one fluorine ligand from the unstable SF? radical to give the stable closed-shell SF? molecule. Similarly, the BDE for the removal of one fluorine ligand from the stable closed-shell PF?O molecule to give the unstable PF?O radical is higher than the BDE needed to remove the oxygen atom to give the stable closed-shell PF? molecule. The same principles govern the BDEs of the phosphorus fluorides and the sulfur oxofluorides. In polyatomic molecules, care must be exercised not to equate BDEs with the bond strengths of given bonds. The measurement of the bond strength or stiffness of a given bond represented by its force constant involves only a small displacement of the atoms near equilibrium and, therefore, does not involve any reorganization energies, i.e., it may be more appropriate to correlate with the diabatic product states.

Grant, Daniel J.; Matus, Myrna H.; Switzer, Jackson R.; Dixon, David A.; Francisco, Joseph S.; Christe, Karl O.

2008-04-10

128

Structure, energy, vibrational spectrum, and Bader's analysis of ?···H hydrogen bonds and H(-?)···H(+?) dihydrogen bonds.  

PubMed

In this paper, the intermolecular structural study asserted by the vibrational analysis in the stretch frequencies of hydrogen bonds (?···H) and dihydrogen bonds (H(-?)···H(+?)) have definitively been revisited by means of calculations carried out by Density Functional Theory (DFT) and topological parameters derived from the classic treatise of the Quantum Theory of Atoms in Molecules (QTAIM). As a matter of fact the ?···H hydrogen bond is formed between the hydrofluoric acid and the C?C bond of the acetylene, but the QTAIM calculations revealed a distortion in this interaction due to the formation of the ternary complex C(2)H(2)···2(HF). Although the ? bonds of ethylene (C(2)H(4)), propylene (C(2)H(3)(CH(3))), and t-butylene (C(2)H(2)(CH(3))(2)) are considered proton acceptors, two hydrogen-bond types--?···H and C···H--can be observed. Over and above the analysis of the ? hydrogen bonds, theoretical arguments also were used to discuss the red-shifts in the stretch frequencies of the binary dihydrogen complexes formed by BeH(2)···HX with X = F, Cl, CN, and CCH. Although a vibrational blue-shift in the stretch frequency of the H-C bond of HCF(3) due to the formation of the BeH(2)···HCF(3) dihydrogen complex was obtained, unmistakable red-shifts were detected in LiH···HCF(3), MgH(2)···HCF(3), and NaH···HCF(3). Moreover, the alkali-halogen bonds were identified in relation to the formation of the trimolecular systems NaH···2(HCF(3)) and NaH···2(HCCl(3)). At last, theoretical calculations and QTAIM molecular integrations were used to study a novel class of dihydrogen-bonded complexes (mC(2)H(5)(+)···nMgH(2) with m = 1 or 2 and n = 1 or 2) based in the insight that MgH(2) can bind with the non-localized hydrogen H(+?) of the ethyl cation (C(2)H(5)(+)). In an overview, QTAIM calculations were applied to evaluate the molecular topography, charge density, as well as to interpret the shifted frequencies either to red or blue caused by the formation of the hydrogen bonds and dihydrogen bonds. PMID:23138158

de Oliveira, Boaz Galdino

2013-01-01

129

Argon hydrochloride, Ar.HCl, bond energy by infrared spectroscopy  

NASA Technical Reports Server (NTRS)

The infrared absorption of argon (200 to 760 torr) and hydrogen chloride (2 to 6 torr) mixtures is reexamined in the missing Q branch region (spectral region between 2860 and 3010 wavelength/cm) at temperatures ranging from 195 to 298 K. The temperature dependence of two absorption features of the argon hydrogen chloride complex, at 2887 and 2879 wavelength/cm, leads to a bond energy estimate that depends on the assumptions made about the internal degrees of freedom of the complex. It is shown that agreement with experiment can be reached for well depths near 1.2 kcal/mole. This result is relatively insensitive to the choice of the vibrational frequencies and anharmonicities, but does depend on the extent to which the energy level manifolds are truncated to avoid molecular excitation in excess of the bond energy. The bond energy is found to deviate from the commonly accepted value of 0.4 kcal/mole. Possible causes for the discrepancy are considered.

Miziolek, A. W.; Pimentel, G. C.

1976-01-01

130

Bond Dissociation Energies for Substituted Polycyclic Aromatic Hydrocarbons and Their Cations  

NASA Technical Reports Server (NTRS)

The B3LYP/4-31G approach is used to compute bond energies for a series of substituted benzene, naphthalene, and anthracene molecules and their cations. The benzene bond energies are compared with experiment. The trends in the bond energies are discussed. The ionization energies are also reported and compared with available experiments.

Bauschlicher, Charles W.; Langhoff, Stephen R.; Arnold, James O. (Technical Monitor)

1998-01-01

131

Intramolecular hydrogen bonding as reflected in the deuterium isotope effects on carbon-13 chemical shifts. Correlation with hydrogen bond energies  

SciTech Connect

The carbon-13 resonances of atoms bearing phenolic or enolic hydroxyl groups, that are engaged in intramolecular hydrogen bonds, experience large (/sup 2/..delta.. may exceed 1 ppm) upfield deuterium isotope effects. The magnitude of the two-bond isotope effect, /sup 2/..delta.., correlates with the hydrogen bond energy as obtained from the hydroxyl proton chemical shift. In the conjugated systems investigated in this work, the isotope effects extend over several (up to six) chemical bonds. The signs and magnitudes of the long-range isotope effects are related to molecular structure.

Reuben, J.

1986-04-16

132

IR Spectra and Bond Energies Computed Using DFT  

NASA Technical Reports Server (NTRS)

The combination of density functional theory (DFT) frequencies and infrared (IR) intensities and experimental spectra is a very powerful tool in the identification of molecules and ions. The computed and measured isotopic ratios make the identification much more secure than frequencies and intensities alone. This will be illustrated using several examples, such as Mn(CO)n and Mn(CO)n-. The accuracy of DFT metal-ligand bond energies will also be discussed.

Bauschlicher, Charles; Andrews, Lester; Arnold, James (Technical Monitor)

2000-01-01

133

Bond length and local energy density property connections for non-transition-metal oxide-bonded interactions.  

PubMed

For a variety of molecules and earth materials, the theoretical local kinetic energy density, G(r(c)), increases and the local potential energy density, V(r(c)), decreases as the M-O bond lengths (M = first- and second-row metal atoms bonded to O) decrease and the electron density, rho(r(c)), accumulates at the bond critical points, r(c). Despite the claim that the local kinetic energy density per electronic charge, G(r(c))/rho(r(c)), classifies bonded interactions as shared interactions when less than unity and closed-shell when greater, the ratio was found to increase from 0.5 to 2.5 au as the local electronic energy density, H(r(c)) = G(r(c)) + V(r(c)), decreases and becomes progressively more negative. The ratio appears to be a measure of the character of a given M-O bonded interaction, the greater the ratio, the larger the value of rho(r(c)), the smaller the coordination number of the M atom and the more shared the bonded interaction. H(r(c))/rho(r(c)) versus G(r(c))/rho(r(c)) scatter diagrams categorize the M-O bonded interactions into domains with the local electronic energy density per electron charge, H(r(c))/rho(r(c)), tending to decrease as the electronegativity differences for the bonded pairs of atoms decrease. The values of G(r(c)) and V(r(c)), estimated with a gradient-corrected electron gas theory expression and the local virial theorem, are in good agreement with theoretical values, particularly for the bonded interactions involving second-row M atoms. The agreement is poorer for shared C-O and N-O bonded interactions. PMID:17078623

Gibbs, G V; Spackman, M A; Jayatilaka, D; Rosso, K M; Cox, D F

2006-11-01

134

Bond Length and Local Energy Density Property Connections for Non-transition- Metal-Oxide-Bonded Interactions  

SciTech Connect

For a variety of molecules and Earth materials, the theoretical local kinetic energy density, G(rc), increases and the local potential energy density, V(rc), decreases as the MO bond lengths (M = first and second row metal atoms) decrease and electron density, ?(rc), is localized at the bond critical points, rc. Despite claims that the ratio, G(rc)/?(rc), classifies bonded interactions as shared covalent when less than unity and closed shell ionic when greater than unity, the ratio was found to increase from 0.5 to 2.5 a.u. as the local electronic energy density H(rc) = G(rc) + V(rc) decreases and becomes progressively more negative. In any event, the ratio is indicated to be a measure of the character for a given M-O bond, the greater the ratio, the larger the value of ?(rc), the smaller the coordination number of the M atom and the more covalent the bond. H(rc)/?(rc) vs. G(rc)/?(rc) scatter diagrams categorize the M-O bond data into domains with the H(rc)/?(rc) ratio tending to increase as the electronegativity of the M atoms increase. Estimated values of G(rc) and V(rc), using an expression based on gradient corrected electron gas theory, are in good agreement with theoretical values, particularly for bonded interactions involving second row M atoms. The agreement is poorer for the more covalent C-O and N-O bonds.

Gibbs, Gerald V.; Spackman, M. A.; Jayatilaka, Dylan; Rosso, Kevin M.; Cox, David F.

2006-11-09

135

Ubiquitous Transgenic Overexpression of C-C Chemokine Ligand 2: A Model to Assess the Combined Effect of High Energy Intake and Continuous Low-Grade Inflammation  

PubMed Central

Excessive energy management leads to low-grade, chronic inflammation, which is a significant factor predicting noncommunicable diseases. In turn, inflammation, oxidation, and metabolism are associated with the course of these diseases; mitochondrial dysfunction seems to be at the crossroads of mutual relationships. The migration of immune cells during inflammation is governed by the interaction between chemokines and chemokine receptors. Chemokines, especially C-C-chemokine ligand 2 (CCL2), have a variety of additional functions that are involved in the maintenance of normal metabolism. It is our hypothesis that a ubiquitous and continuous secretion of CCL2 may represent an animal model of low-grade chronic inflammation that, in the presence of an energy surplus, could help to ascertain the afore-mentioned relationships and/or to search for specific therapeutic approaches. Here, we present preliminary data on a mouse model created by using targeted gene knock-in technology to integrate an additional copy of the CCl2 gene in the Gt(ROSA)26Sor locus of the mouse genome via homologous recombination in embryonic stem cells. Short-term dietary manipulations were assessed and the findings include metabolic disturbances, premature death, and the manipulation of macrophage plasticity and autophagy. These results raise a number of mechanistic questions for future study.

Rodriguez-Gallego, Esther; Hernandez-Aguilera, Anna; Marine-Casado, Roger; Rull, Anna; Beltran-Debon, Raul; Menendez, Javier A.; Vazquez-Martin, Alejandro; Sirvent, Juan J.; Martin-Paredero, Vicente; Corbi, Angel L.; Sierra-Filardi, Elena; Aragones, Gerard; Garcia-Heredia, Anabel; Camps, Jordi; Alonso-Villaverde, Carlos; Joven, Jorge

2013-01-01

136

Structures, energies, and bonding in the water heptamer  

NASA Astrophysics Data System (ADS)

In this paper we report the geometries and properties of 38 distinct geometrical motifs located on the B3LYP/6-31+G(d), MP2/6-311++G(d, p) potential energy surfaces of the water heptamer. Binding energies of up to 45 kcal/mol are calculated. All motifs fall within 10 kcal/mol of the most stable conformation, with at least 13 structural patterns located no more than 3 kcal/mol above, leading to a very complex potential energy surface, populated by a multitude of motifs each one allowing large numbers of conformations. Cluster stability does not seem to be correlated with the number of hydrogen bonds. Compact structures are energetically favored by electronic energies with zero-point energy corrections, while more open structures are preferred when temperature and entropy are accounted for. The molecular interactions holding the clusters as discrete units lead to large binding energies but are not strong enough to cause significant changes in the geometries of the interacting monomers. Our results indicate that bonding in the water heptamers can be considered as largely non-shared interactions with contributions from intermediate character of increasing covalency.

Acelas, Nancy; Hincapié, Gina; Guerra, Doris; David, Jorge; Restrepo, Albeiro

2013-07-01

137

Catalytic Carbonyl Allylation, Propargylation and Vinylation from the Alcohol or Aldehyde Oxidation Level via C-C Bond Forming Hydrogenation and Transfer Hydrogenation: A Departure from Preformed Organometallic Reagents**  

PubMed Central

Classical protocols for carbonyl allylation, propargylation and vinylation typically rely upon the use of preformed allyl metal, allenyl metal and vinyl metal reagents, respectively, mandating stoichiometric generation of metallic byproducts. Through transfer hydrogenative C-C coupling, carbonyl addition may be achieved from the aldehyde or alcohol oxidation level in the absence of stoichiometric organometallic reagents or metallic reductants. Here, we review transfer hydrogenative methods for carbonyl addition, which encompass the first cataltyic protocols enabling direct C–H functionalization of alcohols.

Bower, John F.; Kim, In Su; Patman, Ryan L.; Krische, Michael J.

2009-01-01

138

Measuring the energy landscape of complex bonds using AFM  

NASA Astrophysics Data System (ADS)

We measured rupture force of a complex bond of two interacting proteins with atomic force microscopy. Proteins of interest were active and latent Matrix metalloproteinases (MMPs), type 2 and 9, and their tissue inhibitors TIMP1 and TIMP2. Measurements show that the rupture force depends on the pulling speed; it ranges from 30 pN to 150 pN at pulling speeds 30nm/s to 48000nm/s. Analyzing data using an extended theory enabled us to understand the mechanism of MMP-TIMP interaction; we determined all physical parameters that form the landscape energy of the interaction, in addition to the life time of the bond and its length. Moreover, we used the pulling experiment to study the interaction of TIMP2 with the receptor MT1-MMP on the surface of living cells.

Mayyas, Essa; Hoffmann, Peter; Runyan, Lindsay

2009-03-01

139

Samarium(III)-catalyzed C(sp3)-H bond activation: synthesis of indolizines via C-C and C-N coupling between 2-alkylazaarenes and propargylic alcohols.  

PubMed

A new rare earth metal and samarium-catalyzed C(sp(3))-H bond activation is reported in which 2-alkylazaarenes and propargylic alcohols were converted to indolizines. This process operates under mild conditions and solvent-free conditions. A broad scope of coupling partners has been established, and a likely mechanism has also been suggested. PMID:24359214

Wang, Xu; Li, Shen-yan; Pan, Ying-ming; Wang, Heng-shan; Liang, Hong; Chen, Zhen-feng; Qin, Xiao-huan

2014-01-17

140

Neutral and ionic metal methyl bond energies: Zn  

SciTech Connect

Zinc methyl and zinc methyl ion are two competing products studied in the ion beam reactions of Zn/sup +/ with a series of alkanes. While ion beam techniques have long been used to provide bond dissociation energies for ionic transition metal species, including MCH/sub 3//sup +/, this study is one of the first to test the reliability of the technique. In addition, improved instrumentation makes possible the determination of both ionic and neutral bond energies. We determine D/sup 0/(Zn/sup +/-CH/sub 3/) = 3.06 +- 0.14 eV (70.6 +- 3.2 kcal/mol) and D/sup 0/(Zn-CH/sub 3/) = 0.84 +- 0.14 eV (19.4 +- 3.2 kcal/mol), both in excellent agreement with the available literature. Coupled with literature thermochemistry, this latter value implies that D/sup 0/(CH/sub 3/Zn-CH/sub 3/) = 69.5 +- 3.2 kcal/mol. General features of the reaction cross sections and branching ratios are discussed in terms of a simple qualitative molecular orbital picture.

Georgiadis, R.; Armentrout, P.B.

1986-04-30

141

The Trouble with Chemical Energy: Why Understanding Bond Energies Requires an Interdisciplinary Systems Approach  

ERIC Educational Resources Information Center

Helping students understand "chemical energy" is notoriously difficult. Many hold inconsistent ideas about what energy is, how and why it changes during the course of a chemical reaction, and how these changes are related to bond energies and reaction dynamics. There are (at least) three major sources for this problem: 1) the way biologists talk…

Cooper, Melanie M.; Klymkowsky, Michael W.

2013-01-01

142

Characterization of the thermosonic wire bonding technique. [Combination of ultrasonic energy and thermocompression  

Microsoft Academic Search

This study was designed to evaluate the combination of ultrasonic energy and thermocompression techniques with regard to the bond response of thin film substrate metallization and thick film discrete component terminations. The object was to determine not only the quality of thermosonic gold wire bonds and the performance of these bonds when subjected to thermal environmental tests, but also to

D. R. Johnson; E. L. Chavez

1976-01-01

143

Kinetics, thermodynamics, and effect of BPh3 on competitive C-C and C-H bond activation reactions in the interconversion of allyl cyanide by [Ni(dippe)].  

PubMed

Reaction of [(dippe)Ni(micro-H)](2) with allyl cyanide at low temperature quantitatively generates the eta(2)-olefin complex (dippe)Ni(CH(2)=CHCH(2)CN) (1). At ambient temperature or above, the olefin complex is converted to a mixture of C-CN cleavage product (dippe)Ni(eta(3)-allyl)(CN) (3) and the olefin-isomerization products (dippe)Ni(eta(2)-crotonitrile) (cis- and trans-2), which form via C-H activation. The latter are the exclusive products at longer reaction times, indicating that C-CN cleavage is reversible and the crotononitrile complexes 2 are more thermodynamically stable than eta(3)-allyl species 3. The kinetics of this reaction have been followed as a function of temperature, and rate constants have been extracted by modeling of the reaction. The rate constants for C-CN bond formation (the reverse of C-CN cleavage) show a stronger temperature dependence than those for C-CN and C-H activation, making the observed distribution of C-H versus C-CN cleavage products strongly temperature-dependent. The activation parameters for the C-CN formation step are also quite distinct from those of the C-CN and C-H cleavage steps (larger DeltaH(++) and positive DeltaS(++)). Addition of the Lewis acid BPh(3) to 1 at low temperature yields exclusively the C-CN activation product (dippe)Ni(eta(3)-allyl)(CNBPh(3)) (4). Independently prepared (dippe)Ni(crotononitrile-BPh(3)) (cis- and trans-7) does not interconvert with 4, indicating that 4 is the kinetic product of the BPh(3)-mediated reaction. On standing in solution at ambient temperature, 4 decomposes slowly to complex 5, with structure [(dippe)Ni(eta(3)-allyl)(N triple bond C-BPh(3)), while addition of a second equivalent of BPh(3) immediately produces [(dippe)Ni(eta(3)-allyl)](+)[Ph(3)BC triple bond NBPh(3)](-) (6). Comparison of the barriers to pi-sigma allyl interconversion (determined via dynamic (1)H NMR spectroscopy) for all of the eta(3)-allyl complexes reveals that axial cyanide ligands facilitate pi-sigma interconversion by moving into the P(2)Ni square plane when the allyl group is sigma-bound. PMID:15025492

Brunkan, Nicole M; Brestensky, Donna M; Jones, William D

2004-03-24

144

Calculation of activation energies for hydrogen-atom abstractions by radicals containing carbon triple bonds  

NASA Technical Reports Server (NTRS)

Activation energies are calculated by the bond-energy-bond-order (BEBO) and the bond-strength-bond-length (BSBL) methods for the reactions of C2H radicals with H2, CH4, and C2H6 and for the reactions of CN radicals with H2 and CH4. The BSBL technique accurately predicts the activation energies for these reactions while the BEBO method yields energies averaging 9 kcal higher than those observed. A possible reason for the disagreement is considered.

Brown, R. L.; Laufer, A. H.

1981-01-01

145

Classification of metal-oxide bonded interactions based on local potential- and kinetic-energy densities  

SciTech Connect

A classification of the HF bonded interactions comprising a large number of molecules has been proposed by Espinosa et al. [J. Chem. Phys. 117, 5529 (2002)] based on the ratio |V(rc)|/G(rc) where |V(rc)| is the magnitude of the local potential energy density and G(rc) is the local kinetic density evaluated at the bond critical points, rc. A calculation of the ratio for the MO bonded interactions comprising a relatively large number of molecules and earth materials, together with the constraints imposed by the values of Ñ2?(rc) and the local electronic energy density H(rc) = G(rc) + V(rc) in the HF study, yielded the same classification for the oxides as found for the fluorides. This is true despite the different trends of the bond critical point and local energy properties with the bond length displayed by the HF and MO bonded interactions. LiO, NaO and MgO bonded interactions classify as closed shell ionic bonds, BeO, AlO, SiO, BO and PO bonded interactions classify as bonds of intermediate character and NO bonded interactions classify as shared covalent bonds. CO and SO bonded interactions classify as both intermediate and covalent bonded interactions. The CO triple bonded interaction classifies as a bond of intermediate character and the CO single bonded interaction classifies as a covalent bond whereas their H(rc) value indicates that they are both covalent bonds. The |V(rc)|/G(rc) ratios for the BeO, AlO and SiO bonded interactions indicate that they have a substantial component of ionic character despite their classification as bonds of intermediate character. The trend between |V(rc)|/G(rc) and the character of the bonded interaction is consistent with trends expected from electronegativity considerations. The connection between the net charges and the experimental SiO bond length evaluated for the Si and O atoms comprising two orthosilicates are examined in terms of the |V(rc)|/G(rc) values.

Gibbs, Gerald V.; Cox, David; Crawford, T Daniel; Rosso, Kevin M.; Ross, Nancy; Downs, R. T.

2006-02-28

146

C-F or C-H bond activation and C-C coupling reactions of fluorinated pyridines at rhodium: synthesis, structure and reactivity of a variety of tetrafluoropyridyl complexes.  

PubMed

Reactions of [RhH(PEt3)3] (1) or [RhH(PEt3)4] (2) with pentafluoropyridine or 2,3,5,6-tetrafluoropyridine afford the activation product [Rh(4-C5NF4)(PEt3)3] (3). Treatment of 3 with CO, 13CO or CNtBu effects the formation of trans-[Rh(4-C5NF4)(CO)(PEt3)2] (4a), trans-[Rh(4-C5NF4)(13CO)(PEt3)2] (4b) and trans-[Rh(4-C5NF4)(CNtBu)(PEt3)2] (5). The rhodium(III) compounds trans-[RhI(CH3)(4-C5NF4)(PEt3)2] (6a) and trans-[RhI(13CH3)(4-C5NF4)(PEt3)2] (6b) are accessible on reaction of 3 with CH3I or 13CH3I. In the presence of CO or 13CO these complexes convert into trans-[RhI(CH3)(4-C5NF4)(CO)(PEt3)2] (7a), trans-[RhI(13CH3)(4-C5NF4)(CO)(PEt3)2] (7b) and trans-[RhI(13CH3)(4-C5NF4)(13CO)(PEt3)2] (7c). The trans arrangement of the carbonyl and methyl ligand in 7a-7c has been confirmed by the 13C-13C coupling constant in the 13C NMR spectrum of 7c. A reaction of 4a or 4b with CH3I or 13CH3I yields the acyl compounds trans-[RhI(COCH3)(4-C5NF4)(PEt3)2] (8a) and trans-[RhI(13CO13CH3)(4-C5NF4)(PEt3)2] (8b), respectively. Complex 8a slowly reacts with more CH3I to give [PEt3Me][Rh(I)2(COCH3)(4-C5NF4)(PEt3)](9). On heating a solution of 7a, the complex trans-[RhI(CO)(PEt3)2] (10) and the C-C coupled product 4-methyltetrafluoropyridine (11) have been obtained. Complex 8a also forms 10 at elevated temperatures in the presence of CO together with the new ketone 4-acetyltetrafluoropyridine (12). The structures of the complexes 3, 4a, 5, 6a, 8a and 9 have been determined by X-ray crystallography. 19F-1H HMQC NMR solution spectra of 6a and 8a reveal a close contact of the methyl groups in the phosphine to the methyl or acyl ligand bound at rhodium. PMID:15573161

Noveski, Daniel; Braun, Thomas; Neumann, Beate; Stammler, Anja; Stammler, Hans-Georg

2004-12-21

147

Hydrogen-mediated reductive coupling of conjugated alkynes with ethyl (N-Sulfinyl)iminoacetates: synthesis of unnatural alpha-amino acids via rhodium-catalyzed C-C bond forming hydrogenation.  

PubMed

Rhodium-catalyzed hydrogenation of 1,3-enynes 1a-8a and 1,3-diynes 9a-13a at ambient temperature and pressure in the presence of ethyl (N-tert-butanesulfinyl)iminoacetate and ethyl (N-2,4,6-triisopropylbenzenesulfinyl)iminoacetates, respectively, results in reductive coupling to afford unsaturated alpha-amino acid esters 1b-13b in good to excellent yields with exceptional levels of regio- and stereocontrol. Further hydrogenation of the diene containing alpha-amino acid esters 1b-8b using Wilkinson's catalyst at ambient temperature and pressure results in regioselective reduction to afford the beta,gamma-unsaturated alpha-amino acid esters 1c-8c in good to excellent yields. Exhaustive hydrogenation of the unsaturated side chains of the Boc- and Fmoc-protected derivatives of enyne and diyne coupling products 14b-16b occurs in excellent yield using Crabtree's catalyst at ambient temperature and pressure providing the alpha-amino acid esters 14d-16d, which possess saturated side chains. Finally, cross-metathesis of the Boc-protected reductive coupling product 14b with cis-1,4-diacetoxy-2-butene proceeds readily to afford the allylic acetate 14e. Isotopic labeling studies that involve reductive coupling of enyne 1a and diyne 9a under an atmosphere of elemental deuterium corroborate a catalytic mechanism in which oxidative coupling of the alkyne and imine residues is followed by hydrogenolytic cleavage of the resulting metallacycle. A stereochemical model accounting for the observed sense of asymmetric induction is provided. These studies represent the first use of imines as electrophilic partners in hydrogen-mediated reductive carbon-carbon bond formation. PMID:16089454

Kong, Jong-Rock; Cho, Chang-Woo; Krische, Michael J

2005-08-17

148

Interstellar Isomers: The Importance of Bonding Energy Differences  

NASA Technical Reports Server (NTRS)

We present strong detections of methyl cyanide (CH3CN), vinyl cyanide (CH2CHCN), ethyl cyanide (CH3CH2CN) and cyanodiacetylene (HC4CN) molecules with the Green Bank Telescope (GBT) toward the Sgr B2(N) molecular cloud. Attempts to detect the corresponding isocyanide isomers were only successful in the case of methyl isocyanide (CH3NC) for its J(sub K) = 1(sub 0) - 0(sub 0) transition, which is the first interstellar report of this line. To determine the spatial distribution of CH3NC, we used archival Berkeley-Illinois-Maryland Association (BIMA) array data for the J(sub K) = 1(sub 0) - 0(sub 0) transitions but no emission was detected. From ab initio calculations, the bonding energy difference between the cyanide and isocyanide molecules is greater than 8500 per centimeter (greater than 12,000 K). Thus, cyanides are the more stable isomers and would likely be formed more preferentially over their isocyanide counterparts. That we detect CH3NC emission with a single antenna (Gaussian beamsize(omega(sub B))=1723 arcsec(sup 2)) but not with an interferometer (omega(sub b)=192 arcsec(sup 2)), strongly suggests that CH3NC has a widespread spatial distribution toward the Sgr B2(N) region. Other investigators have shown that CH3CN is present both in the LMH hot core of Sgr B2(N) and in the surrounding medium, while we have shown that CH3NC appears to be deficient in the LMH hot core. Thus, largescale, non-thermal processes in the surrounding medium may account for the conversion of CH3CN to CH3NC while the LMH hot core, which is dominated by thermal processes, does not produce a significant amount of CH3NC. Ice analog experiments by other investigators have shown that radiation bombardment of CH3CN can produce CH3NC, thus supporting our observations. We conclude that isomers separated by such large bonding energy differences are distributed in different interstellar environments, making the evaluation of column density ratios between such isomers irrelevant unless it can be independently shown that these species are co-spatial.

Remijan, Anthony J.; Hollis, J. M.; Lovas, F. J.; Plusquellic, D. F.; Jewell, P. R.

2005-01-01

149

C. C. Jones: Scientific Photographs  

NSDL National Science Digital Library

This image gallery, by C. C. Jones of Union College, contains many examples of physical optics and also x-ray diffraction. Several images of diffraction show how the pattern changes when the wavelength, the distance between light sources, and the aperture is varied. Also included are pinhole photos and comparisons of emission spectra of various elements and the absorption spectrum of the sun. Captions provide background information.

2007-04-25

150

Middle School Chemistry: Energy Levels, Electrons, and Ionic Bonding  

NSDL National Science Digital Library

This multimedia lesson for Grades 7-8 features six animations, one video, and a hands-on lab to explore the process of ionic bonding. Learners can visualize what happens when positive and negative ions attract each other and form a bond, build 2D and 3D models, and perform a hands-on activity to observe sodium chloride crystals and relate their shape to the molecular model. Editor's Note: Ionic bonding occurs when electrons are transferred between atoms through electrostatic attraction between two oppositely charged ions. Covalent bonding occurs when electrons are shared between atoms. The processes are quite different. This module very effectively explores the atomic processes that underlie ionic bonding.

Galvan, Patti; Kessler, Jim

2011-08-17

151

Structures, energies and bonding in neutral and charged Li microclusters.  

PubMed

Structural and chemical properties of charged and neutral Lithium microclusters are investigated for [Formula: see text]. A total of 18 quantum conformational spaces are randomly walked to produce candidate structures for local minima. Very rich potential energy surfaces are produced, with the largest structural complexity predicted for anionic clusters. Analysis of the electron charge distributions using the quantum theory of atoms in molecules (QTAIM) predicts major stabilizing roles of Non-nuclear attractors (NNAs) via NNA···Li interactions with virtually no direct Li···Li interactions, except in the least stable configurations. A transition in behavior for clusters containing more than seven nuclei is observed by using the recently introduced quantum topology to determine in a quantum mechanically consistent fashion the number of spatial dimensions each cluster has. We experiment with a novel scheme for extracting persistent structural motifs with increase in cluster size. The new structural motifs correlate well with the energetic stability, particularly in highlighting the least stable structures. Quantifying the degree of covalent character in Lithium bonding independently agrees with the observation in the transition in cluster behavior for lithium clusters containing more than seven nuclei. Good correlation with available experimental data is obtained for all properties reported in this work. PMID:22538507

Yepes, Diana; Kirk, Steven Robert; Jenkins, Samantha; Restrepo, Albeiro

2012-09-01

152

Observation of B+??c+?c-K+ and B0??c+?c-K0 Decays  

NASA Astrophysics Data System (ADS)

We report the first measurements of the doubly charmed baryonic B decays B??c+?c-K. The B+??c+?c-K+ decay is observed with a branching fraction of (6.5-0.9+1.0±1.1±3.4)×10-4 and a statistical significance of 15.4?. The B0??c+?c-K0 decay is observed with a branching fraction of (7.9-2.3+2.9±1.2±4.1)×10-4 and a statistical significance of 6.6?. The branching fraction errors are statistical, systematic, and the error resulting from the uncertainty of the ?c+?pK-?+ decay branching fraction. The analysis is based on 357fb-1 of data accumulated at the ?(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.

Gabyshev, N.; Abe, K.; Abe, K.; Adachi, I.; Aihara, H.; Asano, Y.; Aulchenko, V.; Aushev, T.; Bahinipati, S.; Bakich, A. M.; Balagura, V.; Barberio, E.; Bartel, W.; Bay, A.; Bedny, I.; Bitenc, U.; Bizjak, I.; Bondar, A.; Bozek, A.; Bra?ko, M.; Browder, T. E.; Chen, A.; Chen, W. T.; Cheon, B. G.; Chistov, R.; Choi, Y.; Chuvikov, A.; Cole, S.; Dalseno, J.; Danilov, M.; Dash, M.; Drutskoy, A.; Eidelman, S.; Garmash, A.; Gershon, T.; Gokhroo, G.; Golob, B.; Haba, J.; Hayasaka, K.; Hayashii, H.; Hazumi, M.; Hokuue, T.; Hoshi, Y.; Hou, S.; Hou, W.-S.; Hsiung, Y. B.; Ikado, K.; Imoto, A.; Inami, K.; Itoh, R.; Iwasaki, M.; Iwasaki, Y.; Kang, J. H.; Kawasaki, T.; Khan, H. R.; Kichimi, H.; Kim, S. M.; Korpar, S.; Krokovny, P.; Kulasiri, R.; Kuo, C. C.; Kuzmin, A.; Kwon, Y.-J.; Leder, G.; Lesiak, T.; Lin, S.-W.; Liventsev, D.; Majumder, G.; Matsumoto, T.; Mitaroff, W.; Miyabayashi, K.; Miyata, H.; Miyazaki, Y.; Mizuk, R.; Nakano, E.; Nakao, M.; Natkaniec, Z.; Nishida, S.; Ogawa, S.; Ohshima, T.; Okabe, T.; Okuno, S.; Olsen, S. L.; Ozaki, H.; Palka, H.; Park, C. W.; Park, K. S.; Pestotnik, R.; Piilonen, L. E.; Sakai, Y.; Sato, N.; Satoyama, N.; Schietinger, T.; Schneider, O.; Schwanda, C.; Seidl, R.; Senyo, K.; Sevior, M. E.; Shapkin, M.; Shibuya, H.; Somov, A.; Soni, N.; Stamen, R.; Stani?, S.; Stari?, M.; Sumiyoshi, T.; Tamai, K.; Tamura, N.; Tanaka, M.; Taylor, G. N.; Teramoto, Y.; Tian, X. C.; Tsukamoto, T.; Uehara, S.; Uglov, T.; Ueno, K.; Uno, S.; Urquijo, P.; Varner, G.; Varvell, K. E.; Villa, S.; Wang, C. C.; Wang, C. H.; Watanabe, Y.; Won, E.; Xie, Q. L.; Yamaguchi, A.; Yamauchi, M.; Ying, J.; Zhang, Z. P.

2006-11-01

153

Bipodal surface organometallic complexes with surface N-donor ligands and application to the catalytic cleavage of C-H and C-C bonds in n-butane.  

PubMed

We present a new generation of "true vicinal" functions well-distributed on the inner surface of SBA15: [(?Si-NH2)(?Si-OH)] (1) and [(?Si-NH2)2] (2). From these amine-modified SBA15s, two new well-defined surface organometallic species [(?Si-NH-)(?Si-O-)]Zr(CH2tBu)2 (3) and [(?Si-NH-)2]Zr(CH2tBu)2 (4) have been obtained by reaction with Zr(CH2tBu)4. The surfaces were characterized with 2D multiple-quantum (1)H-(1)H NMR and infrared spectroscopies. Energy-filtered transmission electron microscopy (EFTEM), mass balance, and elemental analysis unambiguously proved that Zr(CH2tBu)4 reacts with these vicinal amine-modified surfaces to give mainly bipodal bis(neopentyl)zirconium complexes (3) and (4), uniformly distributed in the channels of SBA15. (3) and (4) react with hydrogen to give the homologous hydrides (5) and (6). Hydrogenolysis of n-butane catalyzed by these hydrides was carried out at low temperature (100 °C) and low pressure (1 atm). While (6) exhibits a bis(silylamido)zirconium bishydride, [(?Si-NH-)2]Zr(H)2 (6a) (60%), and a bis(silylamido)silyloxozirconium monohydride, [(?Si-NH-)2(?Si-O-)]ZrH (6b) (40%), (5) displays a new surface organometallic complex characterized by an (1)H NMR signal at 14.46 ppm. The latter is assigned to a (silylimido)(silyloxo)zirconium monohydride, [(?Si-N?)(?Si-O-)]ZrH (5b) (30%), coexistent with a (silylamido)(silyloxo)zirconium bishydride, [(?Si-NH-)(?Si-O-)]Zr(H)2 (5a) (45%), and a silylamidobis(silyloxo)zirconium monohydride, [(?Si-NH-)(?Si-O-)2]ZrH (5c) (25%). Surprisingly, nitrogen surface ligands possess catalytic properties already encountered with silicon oxide surfaces, but interestingly, catalyst (5) with chelating [N,O] shows better activity than (6) with chelating [N,N]. PMID:24195760

Bendjeriou-Sedjerari, Anissa; Azzi, Joachim M; Abou-Hamad, Edy; Anjum, Dalaver H; Pasha, Fahran A; Huang, Kuo-Wei; Emsley, Lyndon; Basset, Jean-Marie

2013-11-27

154

A bond-bond description of the intermolecular interaction energy: the case of the weakly bound acetylene-hydrogen complex.  

PubMed

A new semiempirical potential energy surface (PES) for the acetylene-hydrogen system has been derived by using the recently introduced bond-bond methodology. The proposed PES, expressed in an analytic form suitable for molecular dynamics simulations, involves a limited number of parameters, each one having a physical meaning and allowing the accurate description of the system also in the less stable configurations. The analysis of novel integral cross sections data, measured with nearly effusive molecular beams, combined with that of available pressure broadening coefficients of isotropic Raman lines at 143 K and IR lines at 173 and 295 K of C(2)H(2) in H(2), provides a test of the reliability of the proposed PES and suggests also some refinements. An extensive comparison with a recent ab initio potential is also exploited. PMID:19842658

Thibault, F; Cappelletti, D; Pirani, F; Bartolomei, M

2009-12-31

155

Studies of low-lying triplet states in 1,3-C4F6, c-C4F6 and 2-C4F6 by electron energy-loss spectroscopy and ab initio calculations  

NASA Astrophysics Data System (ADS)

This Letter reports on the first measurements of the lowest lying triplet states as studied by electron energy loss spectroscopy for C4F6 isomers, hexafluoro-1,3-butadiene (1,3-C4F6), hexafluorocyclobutene (c-C4F6) and hexafluoro-2-butyne (2-C4F6). This study has been performed at an incident electron energy of 30 eV, 30°, whilst sweeping the energy loss over the range 2.0-15.0 eV. The electronic state spectroscopy has been investigated and the assignments supported by multi-reference quantum chemical calculations. The transition to the steepest electronic excited potential energy curve, is suggested to be dominant for 2-C4F6, due to the large broadening in its energy profile.

Limão-Vieira, P.; Duflot, D.; Anzai, K.; Kato, H.; Hoshino, M.; Silva, F. Ferreira da; Mogi, D.; Tanioka, T.; Tanaka, H.

2013-06-01

156

Estimation of Bond Dissociation Energies and Radical Stabilization Energies by ESR Spectroscopy  

Microsoft Academic Search

Correlations of various indices of the stability and reactivity of carbon-centered radicals with ESR hyperfine splitting constants have been examined. For a large number of mono- and disubstituted radicals there is a moderately good linear correlation of R-proton hyperfine splitting constants (a(HR)) with radical stabilization enthalpies (RSE) and with BDE(C-H), the C-H bond dissociation energies for the corresponding parent compounds

Jochen J. Brocks; Hans-Dieter Beckhaus; Athelstan L. J. Beckwith; Christoph Ruchardt

1998-01-01

157

Intrinsic affinities of alkali cations for 15-crown-5 and 18-crown-6: Bond dissociation energies of gas-phase M{sup +}-crown ether complexes  

SciTech Connect

Bond dissociation energies (BDEs) of M{sup +}[c-(C{sub 2}H{sub 4}O){sub 5}] and M{sup +}[c-(C{sub 2}H{sub 4}O){sub 6}] for M = Na, K, Rb, and Cs are reported. The BDEs are determined experimentally by analysis of the thresholds for collision-induced dissociation of the cation-crown ether complexes by xenon measured by using guided ion beam mass spectrometry. In all cases, the primary and lowest energy dissociation channel observed experimentally in endothermic loss of the ligand molecule. The cross section thresholds are interpreted to yield 0 and 298 K BDEs after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and unimolecular decay rates. For both 18-crown-6 and 15-crown-5, the BDEs decrease monotonically with increasing cation size. These results indicate that the intrinsic affinity of c-(C{sub 2}H{sub 4}O){sub 5} and c-(C{sub 2}H{sub 4}O){sub 6} for M{sup +} is determined principally by the charge density of the cation not by the ratio of the ionic radius to the cavity size. The BDEs reported here are in fair agreement with recent ab initio calculations at the MP2 level with 6-31+G* basis sets. The experimental values are systematically smaller than the computed values by 8 {+-} 2 kJ/mol per metal-oxygen interaction. The existence of less strongly bound isomers in the experimental apparatus for Rb{sup +}(15-crown-5) and Cs{sup +}(15-crown-5) appears likely, but their absence for Na{sup +} and K{sup +} complexes indicates interesting metal-dependent dynamics to the formation of such isomers.

More, M.B.; Ray, D.; Armentrout, P.B.

1999-01-20

158

A Dynamic Pathway for Stone-Wales Bond Rotation on Carbon Nanotubes through Diamond-Like Bonds  

NASA Technical Reports Server (NTRS)

A new lower energy barrier with a two-step pathway of Stone-Wales (SW) ,ond rotation on carbon nanotubes (CNTs) is found through molecular dynamics (MD) simulations of CNTs under tension. The first step involves going over to a stable sp3-like metastable configuration with half rotated and partially tilted C-C bond. The second step involves going over to the fully rotated C-C bond with the formation of a SW defect in the nanotube. The energy barrier for this two-step dynamic pathway is significantly lower than the previously known static barrier for in-plane rotation of the C-C bond on a tensile strained (> 4%) CNT.

Wei, Chen-Yu; Srivastava, Deepak; Cho, Kyeong-Jae; Menon, Madhu

2003-01-01

159

Classification of metal-oxide bonded interactions based on local potential- and kinetic-energy densities.  

PubMed

A classification of the hydrogen fluoride H-F-bonded interactions comprising a large number of molecules has been proposed by Espinosa et al. [J. Chem. Phys. 117, 5529 (2002)] based on the ratio /Vr(c)/ / Gr(c) where /Vr(c)/ is the magnitude of the local potential-energy density and Gr(c) is the local kinetic-energy density, each evaluated at a bond critical point r(c). A calculation of the ratio for the M-O bonded interactions comprising a relatively large number of oxide molecules and earth materials, together with the constraints imposed by the values of inverted Delta2rho r(c) and the local electronic energy density, Hr(c) = Gr(c) + Vr(c), in the H-F study, yielded practically the same classification for the oxides. This is true despite the different trends that hold between the bond critical point and local energy density properties with the bond lengths displayed by the H-F and M-O bonded interactions. On the basis of the ratio, Li-O, Na-O, and Mg-O bonded interactions classify as closed-shell ionic bonds, Be-O, Al-O, Si-O, B-O, and P-O interactions classify as bonds of intermediate character with the covalent character increasing from Be-O to P-O. N-O interactions classify as shared covalent bonds. C-O and S-O bonded interactions classify as both intermediate and covalent bonded interactions. The C-O double- and triple-bonded interactions classify as intermediate-bonded interactions, each with a substantial component of covalent character and the C-O single-bonded interaction classifies as a covalent bond whereas their local electronic energy density values indicate that they are each covalent bonded interactions. The ratios for the Be-O, Al-O, and Si-O bonded interactions indicate that they have a substantial component of ionic character despite their classification as bonds of intermediate character. The trend between the ratio and the character of the bonded interactions is consistent with trends expected from electronegativity considerations. The ratio increases as the net charges and the coordination numbers for the atoms for several Ni-sulfides decrease. On the contrary, the ratio for the Si-O bonded interactions for the orthosilicate, forsterite, Mg2SiO4, and the high-pressure silica polymorph, stishovite, decreases as the observed net atomic charges and the coordination numbers of Si and O increase in value. The ratio for the Ni-Ni bonded interactions for the Ni-sulfides and bulk Ni metal indicate that the interactions are intermediate in character with a substantial component of ionic character. PMID:16512733

Gibbs, G V; Cox, D F; Crawford, T D; Rosso, K M; Ross, N L; Downs, R T

2006-02-28

160

Hypovalency--a kinetic-energy density description of a 4c-2e bond.  

PubMed

A bond descriptor based on the kinetic energy density, the localized-orbital locator (LOL), is used to characterize the nature of the chemical bond in electron deficient multi-center bonds. The boranes B(2)H(6), B(4)H(4), B(4)H(10), [B(6)H(6)](2-), and [B(6)H(7)](-) serve as prototypical examples of hypovalent 3c-2e and 4c-2e bonding. The kinetic energy density is derived from a set of Kohn-Sham orbitals obtained from pure density functional calculations (PBE/TZVP), and the topology of LOL is analyzed in terms of (3,-3) attractors (Gamma). The B-B-B and B-H-B 3c-2e, and the B-B-H-B 4c-2e bonding situations are defined by their own characteristic LOL profiles. The presence of one attractor in relation to the three or four atoms that are engaged in electron deficient bonding provides sufficient indication of the type of 3c-2e or 4c-2e bond present. For the 4c-2e bond in [B(6)H(7)](-) the LOL analysis is compared to results from an experimental QTAIM study. PMID:19452076

Jacobsen, Heiko

2009-06-01

161

Aerobic synthesis of substituted quinoline from aldehyde and aniline: copper-catalyzed intermolecular C-H active and C-C formative cyclization.  

PubMed

An efficient method for the direct synthesis of substituted quinolines from anilines and aldehydes through C-H functionalization, C-C/C-N bond formation, and C-C bond cleavage has been developed. The method is simple and practical and employs air as an oxidant. PMID:24024912

Yan, Rulong; Liu, Xingxing; Pan, Congming; Zhou, Xiaoqiang; Li, Xiaoni; Kang, Xing; Huang, Guosheng

2013-09-20

162

Bond-energy force-constant relationship for bent XY2, pyramidal XY3 and tetrahedral XY4 molecules  

Microsoft Academic Search

A relation between the force constants and bond energies of polyatomic molecules of bent XY2, pyramidal XY3, and tetrahedral XY4 types has been deduced by employing an approximately separable potential function for the molecules and using specific functional forms for the bonded and nonbonded interactions. To test the validity of the relation deduced, bond energies were calculated from the available

G. Thyagarajan; C. R. Sarma; M. K. Subhedar

1969-01-01

163

An Experimental and Theoretical Study on the Ionization Energies of Polyynes (H-(C = C)n-H; n = 1 - 9)  

SciTech Connect

We present a combined experimental and theoretical work on the ionization energies of polyacetylene -- organic molecules considered as important building blocks to form polycyclic aromatic hydrocarbons (PAHs) in the proto planetary nebulae such as of CRL 618. This set of astrophysical data can be utilized with significant confidence in future astrochemical models of photon-dominated regions and also of the proto planetary nebulae CRL 618. We recommend ionization energies of polyacetylenes from diacetylene up to heptaacetylene with an experimental accuracy of +- 0.05 eV: 10.03 eV (diacetylene), 9.45 eV (triacetylene), 9.08 eV (tetraacetylene), 8.75 eV (pentaacetylene), 8.65 eV (hexaacetylene), and 8.50 eV (heptaacetylene); further, ionization energies and with an accuracy of +- 0.1 eV: 8.32 eV (octaacetylene) and 8.24 eV (nonaacetylene) were computed. Implications of these energies to the redox chemistry involved in the multiply charged metal-ion mediated chemistry of hydrocarbon-rich atmospheres of planets and their moons such as Titan are also discussed.

Kaiser, Ralf I.; Sun, Bian Jian; Lin, Hong Mao; Chang, Agnes H. H.; Mebel, Alexander M.; Kostko, Oleg; Ahmed, Musahid

2010-05-17

164

Bond Graph Modeling and Validation of an Energy Regenerative System for Emulsion Pump Tests  

PubMed Central

The test system for emulsion pump is facing serious challenges due to its huge energy consumption and waste nowadays. To settle this energy issue, a novel energy regenerative system (ERS) for emulsion pump tests is briefly introduced at first. Modeling such an ERS of multienergy domains needs a unified and systematic approach. Bond graph modeling is well suited for this task. The bond graph model of this ERS is developed by first considering the separate components before assembling them together and so is the state-space equation. Both numerical simulation and experiments are carried out to validate the bond graph model of this ERS. Moreover the simulation and experiments results show that this ERS not only satisfies the test requirements, but also could save at least 25% of energy consumption as compared to the original test system, demonstrating that it is a promising method of energy regeneration for emulsion pump tests.

Li, Yilei; Zhu, Zhencai; Chen, Guoan

2014-01-01

165

Imaging bond breaking and vibrational energy transfer in small water containing clusters  

NASA Astrophysics Data System (ADS)

This letter presents a brief overview of our recent experimental studies of state-to-state vibrational predissociation (VP) dynamics of small hydrogen bonded (H-bonded) clusters following vibrational excitation. Velocity map imaging (VMI) and resonance-enhanced multiphoton ionization (REMPI) are used to determine accurate bond dissociation energies (D0) of (H2O)2, (H2O)3, HCl-H2O and NH3-H2O. Pair-correlated product energy distributions from the VP of these complexes are also presented and compared to theoretical models. Further insights into mechanisms are obtained from the recent quasi-classical trajectory (QCT) calculations of Bowman and coworkers. The D0 values for (H2O)2 and (H2O)3 are in very good agreement with recent calculated values, and the results are used to estimate the contributions of cooperative interactions to the H-bonding network.

Samanta, Amit K.; Ch'ng, Lee C.; Reisler, Hanna

2013-06-01

166

Ultraviolet Bonding of PFPE With Carbon Overcoat: Surface Energy and Spreading  

Microsoft Academic Search

Ultraviolet (UV) irradiation effects on the functional perfluoropolyether (PFPE), i.e., Ztetraol films, were investigated by studying the bonded film thickness as well as the surface energy of PFPE lubricated media using Lifshitz-van der Waals and Lewis acid\\/base (LW\\/AB) theory. It was found that short-time UV irradiation enhanced the bonding of Ztetraol film with ion beam deposited carbon overcoat, which is

Haigang Chen; Pil Seung Chung; Myung S. Jhon

2008-01-01

167

Renewable energy liberation by nonthermal intermolecular bond dissociation in water and ethanol  

NASA Astrophysics Data System (ADS)

Prior indication that renewable energy can be extracted from hydrogen bonds in water has led to several investigations of the energy balance when bulk liquid is converted into micron scale droplets by directional (nonthermal) forces. The demonstration of this effect has previously involved pulsed high current arcs in water which produce large electrodynamic forces. Here, we show that renewable energy is also liberated during the creation of droplets by electrostatic forces in electrohydrodynamic atomization (electrospray) experiments. Using both ethanol and water, the energy outputs, primarily the droplet kinetic energy, were always greater than the energy inputs, implying that stored energy was liberated from the liquid. The energetics of generic chemical bonding are investigated to demonstrate that although this discovery was not publicly anticipated, it is consistent with conventional theory. This experimental breakthrough should have a major impact on the quest for renewable energy sources, capable of powering electricity generators.

Graneau, N.; Verdoold, S.; Oudakker, G.; Yurteri, C. U.; Marijnissen, J. C. M.

2011-02-01

168

Bond Dissociation Free Energies (BDFEs) of the Acidic H-A Bonds in HA(*)(-) Radical Anions by Three Different Pathways.  

PubMed

Cleavage of radical anions, HA(*)(-), have been considered to give either H(*) + A(-) (path a) or H(-) + A(*) (path b), and factors determining the preferred mode of cleavage have been discussed. It is conceivable that cleavage to give a proton and a radical dianion, HA(*)(-) right harpoon over left harpoon H(+) + A(*)(2)(-) (path c), might also be feasible. A method, based on a thermodynamic cycle, to estimate the bond dissociation free energy (BDFE) by path c has been devised. Comparison of the BDFEs for cleavage of the radical anions derived from 24 nitroaromatic OH, SH, NH, and CH acids by paths a, b, c has shown that path c is favored thermodynamically. PMID:11667531

Zhao, Yongyu; Bordwell, Frederick G.

1996-09-20

169

Neutral and ionic metal-hydrogen and metal-carbon bond energies: Reactions of Co sup + , Ni sup + , and Cu sup + with ethane, propane, methylpropane, and dimethylpropane  

SciTech Connect

The reactions of Co{sup +}, Ni{sup +}, and Cu{sup +} with a series of alkanes are examined by guided ion beam mass spectrometry. The emphasis of this study is on C-H and C-C bond cleavage channels from which bond dissociation energies for M-H, M-CH{sub 3}, and M{sup +}-CH{sub 3} are derived from the endothermic reaction thresholds. For these three bond energies, we find values (in kilocalories per mole) of 46 {plus minus} 3, 46 {plus minus} 3, and 49.1 {plus minus} 3.5, respectively, for M = Co; 58 {plus minus} 3, 55 {plus minus} 3, and 45.0 {plus minus} 2.4, respectively, for M = Ni; 61 {plus minus} 4, 58 {plus minus} 2, 29.7 {plus minus} 1.7, respectively, for M = Cu. Trends in the thermochemistry of these species and M{sup +}-H are briefly discussed. The reactivity of Cu{sup +}, which has not been previously studied, is compared with that for other transition-metal ions. Also, unusual features in the reactivity of Co{sup +} and Ni{sup +} that have not previously been commented on are discussed.

Georgiadis, R. (Univ. of California, Berkeley (USA)); Fisher, E.R.; Armentrout, P.B. (Univ. of Utah, Salt Lake City (USA))

1989-06-07

170

Iminopropadienones RN=C=C=C=O and bisiminopropadienes RN=C=C=C=NR: matrix infrared spectra and anharmonic frequency calculations.  

PubMed

Methyliminopropadienone MeN=C=C=C=O 1a was generated by flash vacuum thermolysis from four different precursors and isolated in solid argon. The matrix-isolation infrared spectrum is dominated by unusually strong anharmonic effects resulting in complex fine structure of the absorptions due to the NCCCO moiety in the 2200 cm(-1) region. Doubling and tripling of the corresponding absorption bands are observed for phenyliminopropadienone PhN=C=C=C=O 1b and bis(phenylimino)propadiene PhN=C=C=C=NPh 9, respectively. Anharmonic vibrational frequency calculations allow the identification of a number of overtones and combination bands as the cause of the splittings for each molecule. This method constitutes an important tool for the characterization of reactive intermediates and unusual molecules by matrix-isolation infrared spectroscopy. PMID:24182036

Bégué, Didier; Baraille, Isabelle; Andersen, Heidi Gade; Wentrup, Curt

2013-10-28

171

Iminopropadienones RN=C=C=C=O and bisiminopropadienes RN=C=C=C=NR: Matrix infrared spectra and anharmonic frequency calculations  

NASA Astrophysics Data System (ADS)

Methyliminopropadienone MeN=C=C=C=O 1a was generated by flash vacuum thermolysis from four different precursors and isolated in solid argon. The matrix-isolation infrared spectrum is dominated by unusually strong anharmonic effects resulting in complex fine structure of the absorptions due to the NCCCO moiety in the 2200 cm-1 region. Doubling and tripling of the corresponding absorption bands are observed for phenyliminopropadienone PhN=C=C=C=O 1b and bis(phenylimino)propadiene PhN=C=C=C=NPh 9, respectively. Anharmonic vibrational frequency calculations allow the identification of a number of overtones and combination bands as the cause of the splittings for each molecule. This method constitutes an important tool for the characterization of reactive intermediates and unusual molecules by matrix-isolation infrared spectroscopy.

Bégué, Didier; Baraille, Isabelle; Andersen, Heidi Gade; Wentrup, Curt

2013-10-01

172

Strong-bonding calcium phosphate coatings on carbon/carbon composites by ultrasound-assisted anodic oxidation treatment and electrochemical deposition  

NASA Astrophysics Data System (ADS)

The current work describes the ultrasound-assisted anodic oxidation treatment of carbon fiber-reinforced carbon (C/C) composites with H3PO4. The aim was to create chemical bonds between the surface-treated C/C composites and subsequently deposited calcium phosphate (CaP) coatings. The surface energy of C/C obviously increased after undergoing ultrasound-assisted anodic oxidation treatment at a current density of 50 mA/cm2 in aqueous 0.5 M H3PO4 solution (USAT-C/C-50). A large number of O-containing groups and some P-containing groups were found on the treated C/C substrate. The formation of O-containing groups may have been promoted by the energy input of the ultrasound and electric field. P-containing species could be bonded to C/C by Csbnd Psbnd O or Csbnd Osbnd P bonding. Among the species formed, the formation of (H2PO4)- on C/C was promoted by ultrasound. When USAT-C/C-50 was used as the substrate for CaP coatings deposited by ultrasound-assisted electrochemical deposition (USECD), the surface of USAT-C/C-50 acquired strong CaP induction ability, and large amounts of CaP were deposited on it during the initial deposition process. After USECD, very strong-bonding CaP coatings formed on USAT-C/C-50. The average shear bond strength of the coatings obtained on the USAT-C/C-50 substrate [(12.14 ± 1.30) MPa] was about twice that of the coatings obtained on untreated C/C [(6.78 ± 1.06) MPa].

Zhao, Xueni; Li, Hejun; Chen, Mengdi; Li, Kezhi; Wang, Bin; Xu, Zhanwei; Cao, Sheng; Zhang, Leilei; Deng, Hailiang; Lu, Jinhua

2012-04-01

173

Financing Public Sector Projects with Clean Renewable Energy Bonds; Fact Sheet Series on Financing Renewable Energy Projects, National Renewable Energy Laboratory (NREL).  

National Technical Information Service (NTIS)

Clean renewable energy bonds (CREBs) present a low-cost opportunity for public entities to issue bonds to finance renewable energy projects. The federal government lowers the cost of debt by providing a tax credit to the bondholder in lieu of interest pay...

C. Kreycik J. Couglin

2009-01-01

174

Energy transfer mediated by asymmetric hydrogen-bonded interfaces†  

PubMed Central

Amidine-appended ferrocene derivatives form a supramolecular assembly with Ru(ii)(bpy-COOH) (L)22+ complexes (bpy-COOH is 4-CO2H-4?-CH3-bpy and L = bpy, 2,2?-bipyridine or btfmbpy, 4,4?-bis (trifluoromethyl)-2,2?-bipyridine). Steady-state, time-resolved spectroscopy and kinetic isotope effects establish that the metal-to-ligand charge transfer excited states of the Ru(ii) complexes are quenched by proton-coupled energy transfer (PCEnT). These results show that proton motion can be effective in mediating not only electron transfer (ET) but energy transfer (EnT) as well.

Young, Elizabeth R.; Rosenthal, Joel

2013-01-01

175

A new visualization scheme of chemical energy density and bonds in molecules.  

PubMed

Covalent bond describes electron pairing in between a pair of atoms and molecules. The space is partitioned in mutually disjoint regions by using a new concept of the electronic drop region R(D), atmosphere region R(A), and the interface S (Tachibana in J Chem Phys 115:3497-3518, 2001). The covalent bond formation is then characterized by a new concept of the spindle structure. The spindle structure is a geometrical object of a region where principal electronic stress is positive along a line of principal axis of the electronic stress that connects a pair of the R(D)s of atoms and molecules. A new energy density partitioning scheme is obtained using the Rigged quantum electrodynamics (QED). The spindle structure of the stress tensor of chemical bond has been disclosed in the course of the covalent bond formation. The chemical energy density visualization scheme is applied to demonstrate the spindle structures of chemical bonds in H2, C2H6, C2H4 and C2H2 systems. [Figure: see text]. Field theory of the energy density. PMID:15889293

Tachibana, Akitomo

2005-09-01

176

Chemical bond as a test of density-gradient expansions for kinetic and exchange energies  

SciTech Connect

Errors in kinetic and exchange contributions to the molecular bonding energy are assessed for approximate density functionals by reference to near-exact Hartree-Fock values. From the molecular calculations of Allan et al. and of Lee and Ghosh, it is demonstrated that the density-gradient expansion does not accurately describe the noninteracting kinetic contribution to the bonding energy, even when this expansion is carried to fourth order and applied in its spin-density-functional form to accurate Hartree-Fock densities. In a related study, it is demonstrated that the overbinding of molecules such as N/sub 2/ and F/sub 2/, which occurs in the local-spin-density (LSD) approximation for the exchange-correlation energy, is not attributable to errors in the self-consistent LSD densities. Contrary to expectations based upon the Gunnarsson-Jones nodality argument, it is found that the LSD approximation for the exchange energy can seriously overbind a molecule even when bonding does not create additional nodes in the occupied valence orbitals. LSD and exact values for the exchange contribution to the bonding energy are displayed and discussed for several molecules.

Perdew, J.P.; Levy, M.; Painter, G.S.; Wei, S.; Lagowski, J.B.

1988-01-15

177

Rh(I)-catalyzed decarbonylation of diynones via C-C activation: orthogonal synthesis of conjugated diynes.  

PubMed

Utilization of C-C bond activation as a unique mode of reactivity for constructing C-C bonds provides new strategies for preparing important organic molecules. Development of a Rh(I)-catalyzed C-C activation of diynones to synthesize symmetrical and unsymmetrical conjugated diynes through decarbonylation is reported. This C-C cleavage strategy takes advantage of the innate reactivity of conjugated ynones without relying on any ring strain or auxiliary directing group. This alkynation method also has orthogonal properties compared to typical cross-coupling reactions. PMID:23586742

Dermenci, Alpay; Whittaker, Rachel E; Dong, Guangbin

2013-05-01

178

99. Catalog HHistory 1, C.C.C., 23 Guard Rail Construction, Negative ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

99. Catalog H-History 1, C.C.C., 23 Guard Rail Construction, Negative No. P455e (Photographer and date unknown) GUARD RAIL INSTALLATION. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

179

Evaluation of segmented active constrained layer damping treatments that include bonding layer strain energy  

Microsoft Academic Search

The primary objective of this study is to develop a more accurate research and design tool than those in the currently available literature for active constrained layer damping treatments applied in bending. A five layer beam finite element model is presented that includes bonding layer strain energy and extends current finite element models for Euler-Bernoulli beams with segmented active constrained

Peter F. Cento; Grzegorz Kawiecki

2001-01-01

180

Covalent bonding effect on the mean excitation energy of H2 with the local plasma model  

NASA Technical Reports Server (NTRS)

Chemical bonding is taken into account explicitly in the determination of the mean excitation energy (I) for stopping power of H2 with the local plasma approximation by employing molecular electronic wave functions for H2 for the first time. This procedure leads to a new value for IH2 that is higher than all accepted experimental and theoretical values.

Kamaratos, E.

1984-01-01

181

Average bond energies between boron and elements of the fourth, fifth, sixth, and seventh groups of the periodic table  

NASA Technical Reports Server (NTRS)

The average bond energies D(gm)(B-Z) for boron-containing molecules have been calculated by the Pauling geometric-mean equation. These calculated bond energies are compared with the average bond energies D(exp)(B-Z) obtained from experimental data. The higher values of D(exp)(B-Z) in comparison with D(gm)(B-Z) when Z is an element in the fifth, sixth, or seventh periodic group may be attributed to resonance stabilization or double-bond character.

Altshuller, Aubrey P

1955-01-01

182

Phase shift cavity ring down and Fourier transform infrared measurements of C-H vibrational transitions, energy levels, and intensities of (CH3)3Si-C?C-H.  

PubMed

Phase shift cavity ring down and Fourier transform IR techniques have been used to observe the C-H stretch fundamental and overtone absorptions of the acetylenic (?? = 1-5) and methyl (?? = 1-6) C-H bonds of trimethyl-silyl-acetylene [(CH3)3CSi?CH] at 295 K. Harmonic frequencies ?(?1), ?(a), and ?(s) and anharmonicities x(?1), ?(a)x(a), ?(s)x(s) were calculated for the acetylenic, methyl out-of-plane, and methyl in-plane C-H bonds, respectively. The harmonically coupled anharmonic oscillator (HCAO) model was used to determine the overtone energy levels and assign the absorption bands to vibrational transitions of methyl C-H bonds. A hot band, assigned as ??1 + ?24 - ?24 is observed for transitions with ?? = 1-5 in a region near the acetylenic stretch. The intensity of the hot band is reduced considerably at 240 K. The strength of a Fermi resonance between C-Ha transition (??(a)) and the combination band ((?-1)?(a) + 2?(bend)) with (? = 3-6) was calculated using the experimental perturbed energies and relative intensities. The main bands are separated by computer deconvolution and are integrated at each level to get the experimental band strengths. For methyl absorptions, the dipole moment function is expanded as a function of two C-H stretching coordinates and the intensities are calculated in terms of the HCAO model where only the C-H modes are considered. Acetylenic intensities are derived with a one dimensional dipole moment function. The expansion coefficients are obtained from molecular orbital calculations. The intensities are calculated without using adjustable parameters and they are of the same order of magnitude of the experimental intensities for all C-H transitions. PMID:23822307

Barroso, Jenny Z; Perez-Delgado, Yasnahir; Manzanares, Carlos E

2013-07-01

183

Trans-reflection thermal driven deformable mirror with flexible bonding in high energy laser system  

NASA Astrophysics Data System (ADS)

Deformable mirrors used in high energy laser system suffer from problems like the stress from adhesive solidification or the relatively expensive unit price of piezoceramic actuator. The thermal driven deformable mirror (TDDM) investigated here provided a promising prospect to solve these problems. Four scenarios of TDDM were studied and compared. Results showed that the trans-reflection TDDM with flexible bonding best met the requirement in practical use. The flexible bonding excluded the stress problem in the solidification of adhesives, trans-reflection brought about enough correction range, and the choice of thermo-electric cooler as actuator could greatly bring down the cost of adaptive optics apparatus as well.

Ma, Xingkun; Huang, Lei; Gong, Mali; Xue, Qiao

2014-09-01

184

An energetic scale for equilibrium H/D fractionation factors illuminates hydrogen bond free energies in proteins.  

PubMed

Equilibrium H/D fractionation factors have been extensively employed to qualitatively assess hydrogen bond strengths in protein structure, enzyme active sites, and DNA. It remains unclear how fractionation factors correlate with hydrogen bond free energies, however. Here we develop an empirical relationship between fractionation factors and free energy, allowing for the simple and quantitative measurement of hydrogen bond free energies. Applying our empirical relationship to prior fractionation factor studies in proteins, we find: [1] Within the folded state, backbone hydrogen bonds are only marginally stronger on average in ?-helices compared to ?-sheets by ?0.2 kcal/mol. [2] Charge-stabilized hydrogen bonds are stronger than neutral hydrogen bonds by ?2 kcal/mol on average, and can be as strong as -7 kcal/mol. [3] Changes in a few hydrogen bonds during an enzyme catalytic cycle can stabilize an intermediate state by -4.2 kcal/mol. [4] Backbone hydrogen bonds can make a large overall contribution to the energetics of conformational changes, possibly playing an important role in directing conformational changes. [5] Backbone hydrogen bonding becomes more uniform overall upon ligand binding, which may facilitate participation of the entire protein structure in events at the active site. Our energetic scale provides a simple method for further exploration of hydrogen bond free energies. PMID:24501090

Cao, Zheng; Bowie, James U

2014-05-01

185

Physical and chemical transformations of highly compressed carbon dioxide at bond energies.  

PubMed

Carbon dioxide exhibits a richness of high-pressure polymorphs with a great diversity in intermolecular interaction, chemical bonding, and crystal structures. It ranges from typical molecular solids to fully extended covalent solids with crystal structures similar to those of SiO2. These extended solids of carbon dioxide are fundamentally new materials exhibiting interesting optical nonlinearity, low compressibility and high energy density. Furthermore, the large disparity in chemical bonding between the extended network and molecular structures results in a broad metastability domain for these phases to room temperature and almost to ambient pressure and thereby offers enhanced opportunities for novel materials developments. Broadly speaking, these molecular-to-non-molecular transitions occur due to electron delocalization manifested as a rapid increase in electron kinetic energy at high density. The detailed mechanisms, however, are more complex with phase metastabilities, path-dependent phases and phase boundaries, and large lattice strains and structural distortions - all of which are controlled by well beyond thermodynamic constraints to chemical kinetics associated with the governing phases and transitions. As a result, the equilibrium phase boundary is difficult to locate precisely (experimentally or theoretically) and is often obscured by the presence of metastable phases (ordered or disordered). This paper will review the pressure-induced transformations observed in highly compressed carbon dioxide and present chemistry perspectives on those molecular-to-non-molecular transformations that can be applied to other low-Z molecular solids at Mbar pressures where the compression energy rivals the chemical bond energies. PMID:23615853

Yoo, Choong-Shik

2013-06-01

186

Theoretical study of the C-H bond dissociation energy of acetylene  

NASA Technical Reports Server (NTRS)

The authors present a theoretical study of the convergence of the C-H bond dissociation energy (D sub o) of acetylene with respect to both the one- and n-particle spaces. Their best estimate for D sub o of 130.1 plus or minus 1.0 kcal/mole is slightly below previous theoretical estimates, but substantially above the value determined using Stark anticrossing spectroscopy that is asserted to be an upper bound.

Taylor, Peter R.; Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

1990-01-01

187

Atom–bond pairwise additive representation for intermolecular potential energy surfaces  

Microsoft Academic Search

A method has been developed to describe the force field of atomic species interacting with hydrocarbon molecules, either aliphatic or aromatic, of use for molecular dynamics simulations. The potential energy surfaces are represented by a simple analytical form written as a sum of atom–bond interaction contributions, for which a new potential model, [n(x),m], is proposed. The prototypical systems, methane and

F. Pirani; M. Albert??; A. Castro; M. Moix Teixidor; D. Cappelletti

2004-01-01

188

Chalcogen bond: a sister noncovalent bond to halogen bond.  

PubMed

A sister noncovalent bond to halogen bond, termed chalcogen bond, is defined in this article. By selecting the complexes H(2)CS...Cl(-), F(2)CS...Cl(-), OCS...Cl(-), and SCS...Cl(-) as models, the bond-length change, interaction energy, topological property of the electron charge density and its Laplacian, and the charge transfer of the chalcogen bond have been investigated in detail theoretically. It was found that the similar misshaped electron clouds of the chalcogen atom and the halogen atom result in the similar properties of the chalcogen bond and the halogen bond. Experimental results are in good agreement with the theoretical predictions. PMID:19537765

Wang, Weizhou; Ji, Baoming; Zhang, Yu

2009-07-16

189

Students' reasoning about "high-energy bonds" and ATP: A vision of interdisciplinary education  

NASA Astrophysics Data System (ADS)

As interdisciplinary courses are developed, instructors and researchers have to grapple with questions of how students should make connections across disciplines. We explore the issue of interdisciplinary reconciliation (IDR): how students reconcile seemingly contradictory ideas from different disciplines. While IDR has elements in common with other frameworks for the reconciliation of ideas across contexts, it differs in that each disciplinary idea is considered canonically correct within its own discipline. The setting for the research is an introductory physics course for biology majors that seeks to build greater interdisciplinary coherence and therefore includes biologically relevant topics such as adenosine triphosphate (ATP) and chemical bond energy. In our case-study data, students grapple with the apparent contradiction between the energy released when the phosphate bond in ATP is broken and the idea that an energy input is required to break a bond. We see students justifying context-dependent modeling choices, showing nuance in articulating how system choices may be related to disciplinary problems of interest. This represents a desired end point of IDR, in which students can build coherent connections between concepts from different disciplines while understanding each concept in its own disciplinary context. Our case study also illustrates elements of the instructional environment that play roles in the process of IDR.

Dreyfus, Benjamin W.; Sawtelle, Vashti; Turpen, Chandra; Gouvea, Julia; Redish, Edward F.

2014-06-01

190

The influence of interface impurities on fracture energy of UHV diffusion bonded metal-ceramic bicrystals  

SciTech Connect

In both the practical and theoretical aspects of joining metals to ceramics the influence of impurities on the interfacial bond strength is not fully understood. In the present paper the authors describe part of a study in which the interface of niobium-sapphire bicrystals was contaminated under defined conditions and the interfacial fracture energy of these UHV diffusion bonded bicrystals was determined as a measure of their bond strength. The model combination niobium-sapphire shows at high temperatures a simple reaction in which alumina dissolves in niobium without forming an interlayer. Furthermore, niobium and sapphire are characterized by nearly the same expansion behavior which minimizes the development of thermal stresses during cooling down from the bonding temperature. The authors report on experiments in which silver or titanium atoms have been chosen as interfacial impurity elements. Silver is practically insoluble in niobium and sapphire whereas titanium possesses a highly negative free enthalpy of oxide formation. It is assumed that both these properties are associated with interfacially active elements in the system niobium-sapphire.

Elssner, G.; Korn, D.; Ruehle, M. (Max-Planck-Inst. fuer Metallforschung, Stuttgart (Germany). Inst. fuer Werkstoffwissenschaft)

1994-10-15

191

Bond energy and electronic structure in M-bis-terpyridine complexes ( M=Os, Co and Ru)  

NASA Astrophysics Data System (ADS)

We investigate the nature of bond energy and electronic structure of M-bis-terpyridine complexes (M = Os, Co and Ru) using Hartree-Fock and DFT calculations. The nature of bond energy is analyzed using a Morokuma-Kitaura decomposition. DFT results are compared with the Hartree-Fock leading to the conclusion that charge transfer and polarization effects are responsible for the bond energy of the complexes. Also we point out the fact that the electronic configuration of the metallic atom plays a dominant role in the charge transfer process.

Morari, C.

2008-03-01

192

Influence of Buried Hydrogen-Bonding Groups within Monolayer Films on Gas-Surface Energy Exchange and Accommodation  

NASA Astrophysics Data System (ADS)

Self-assembled monolayers (SAMs) of carbonyl-containing alkanethiols on gold are employed to explore the influence of hydrogen-bonding interactions on gas-surface energy exchange and accommodation. H-bonding, COOH-terminated SAMs are found to produce more impulsive scattering and less thermal accommodation than non-H-bonding, COOCH3-terminated monolayers. For carbamate-functionalized SAMs of the form Au/S(CH2)16OCONH(CH2)n-1CH3, impulsive scattering decreases and accommodation increases as the H-bonding group is positioned farther below the terminal CH3.

Ferguson, M. K.; Lohr, J. R.; Day, B. S.; Morris, J. R.

2004-02-01

193

Hydrogen bond energies of 2-aminopyridine dimer and 2-aminopyridine-2-pyridone complex formation  

NASA Astrophysics Data System (ADS)

The formation energies of 2-aminopyridine dimer and 2-aminopyridine-2-pyridone complex were measured in C 6D 6 solution by 1H-NMR spectroscopy and values of 25.1 and 44.6 kJ/mol were obtained. The former value is about twice the magnitude of hydrogen bond energies which are generally observed for the N---H?N system, and latter value is about half the sum of the formation energies of the 2-aminopyridine and 2-pyridone dimers. The formation energies of 2-aminopyridine dimer and 2-aminopyridine-2-pyridone complex were calculated by the CNDO/2 method, and their formation energies (-? H) were estimated to be 28.5 and 42.8 kJ/mol, respectively.

Inuzuka, Kozo; Fujimoto, Akira

194

Columbus Schema for C\\/C++ Preprocessing  

Microsoft Academic Search

File inclusion, conditional compilation and macro pro- cessing has made the C\\/C++ preprocessor a powerful tool for programmers. However, program code with lots of di- rectives often causes difculties in program understanding and maintenance. The main source of the problem is the dif- ference between the code that the programmer sees and the preprocessed code that the compiler gets. To

László Vidács; Árpád Beszédes; Rudolf Ferenc

2004-01-01

195

Hardware synthesis from C\\/C++ models  

Microsoft Academic Search

Software programming languages, such as C\\/C++, have been used as means for specifying hardware for quite a while. Different design methodologies have exploited the advantages of flexibility and fast simulation of models de- scribed with programming languages. At the same time, the mismatch (of software languages) in expressing power (for hardware systems) has caused several difficulties. In the recent past,

Giovanni De Micheli

1999-01-01

196

Topological properties of hydrogen bonds and covalent bonds from charge densities obtained by the maximum entropy method (MEM)  

PubMed Central

Charge densities have been determined by the Maximum Entropy Method (MEM) from the high-resolution, low-temperature (T ? 20?K) X-ray diffraction data of six different crystals of amino acids and peptides. A comparison of dynamic deformation densities of the MEM with static and dynamic deformation densities of multipole models shows that the MEM may lead to a better description of the electron density in hydrogen bonds in cases where the multipole model has been restricted to isotropic displacement parameters and low-order multipoles (l max = 1) for the H atoms. Topological properties at bond critical points (BCPs) are found to depend systematically on the bond length, but with different functions for covalent C—C, C—N and C—O bonds, and for hydrogen bonds together with covalent C—H and N—H bonds. Similar dependencies are known for AIM properties derived from static multipole densities. The ratio of potential and kinetic energy densities |V(BCP)|/G(BCP) is successfully used for a classification of hydrogen bonds according to their distance d(H?O) between the H atom and the acceptor atom. The classification based on MEM densities coincides with the usual classification of hydrogen bonds as strong, intermediate and weak [Jeffrey (1997) ?. An Introduction to Hydrogen Bonding. Oxford University Press]. MEM and procrystal densities lead to similar values of the densities at the BCPs of hydrogen bonds, but differences are shown to prevail, such that it is found that only the true charge density, represented by MEM densities, the multipole model or some other method can lead to the correct characterization of chemical bonding. Our results do not confirm suggestions in the literature that the promolecule density might be sufficient for a characterization of hydrogen bonds.

Netzel, Jeanette; van Smaalen, Sander

2009-01-01

197

Molecular engineering of fracture energy dissipating sacrificial bonds into cellulose nanocrystal nanocomposites.  

PubMed

Even though nanocomposites have provided a plethora of routes to increase stiffness and strength, achieving increased toughness with suppressed catastrophic crack growth has remained more challenging. Inspired by the concepts of mechanically excellent natural nanomaterials, one-component nanocomposites were fabricated involving reinforcing colloidal nanorod cores with polymeric grafts containing supramolecular binding units. The concept is based on mechanically strong native cellulose nanocrystals (CNC) grafted with glassy polymethacrylate polymers, with side chains that contain 2-ureido-4[1H]-pyrimidone (UPy) pendant groups. The interdigitation of the grafts and the ensuing UPy hydrogen bonds bind the nanocomposite network together. Under stress, UPy groups act as sacrificial bonds: simultaneously providing adhesion between the CNCs while allowing them to first orient and then gradually slide past each other, thus dissipating fracture energy. We propose that this architecture involving supramolecular binding units within side chains of polymer grafts attached to colloidal reinforcements opens generic approaches for tough nanocomposites. PMID:24706578

McKee, Jason R; Huokuna, Johannes; Martikainen, Lahja; Karesoja, Mikko; Nykänen, Antti; Kontturi, Eero; Tenhu, Heikki; Ruokolainen, Janne; Ikkala, Olli

2014-05-12

198

Determination of the C4-H bond dissociation energies of NADH models and their radical cations in acetonitrile.  

PubMed

Heterolytic and homolytic bond dissociation energies of the C4-H bonds in ten NADH models (seven 1,4-dihydronicotinamide derivatives, two Hantzsch 1,4-dihydropyridine derivatives, and 9,10-dihydroacridine) and their radical cations in acetonitrile were evaluated by titration calorimetry and electrochemistry, according to the four thermodynamic cycles constructed from the reactions of the NADH models with N,N,N',N'-tetramethyl-p-phenylenediamine radical cation perchlorate in acetonitrile (note: C9-H bond rather than C4-H bond for 9,10-dihydroacridine; however, unless specified, the C9-H bond will be described as a C4-H bond for convenience). The results show that the energetic scales of the heterolytic and homolytic bond dissociation energies of the C4-H bonds cover ranges of 64.2-81.1 and 67.9-73.7 kcal mol(-1) for the neutral NADH models, respectively, and the energetic scales of the heterolytic and homolytic bond dissociation energies of the (C4-H)(.+) bonds cover ranges of 4.1-9.7 and 31.4-43.5 kcal mol(-1) for the radical cations of the NADH models, respectively. Detailed comparison of the two sets of C4-H bond dissociation energies in 1-benzyl-1,4-dihydronicotinamide (BNAH), Hantzsch 1,4-dihydropyridine (HEH), and 9,10-dihydroacridine (AcrH(2)) (as the three most typical NADH models) shows that for BNAH and AcrH(2), the heterolytic C4-H bond dissociation energies are smaller (by 3.62 kcal mol(-1)) and larger (by 7.4 kcal mol(-1)), respectively, than the corresponding homolytic C4-H bond dissociation energy. However, for HEH, the heterolytic C4-H bond dissociation energy (69.3 kcal mol(-1)) is very close to the corresponding homolytic C4-H bond dissociation energy (69.4 kcal mol(-1)). These results suggests that the hydride is released more easily than the corresponding hydrogen atom from BNAH and vice versa for AcrH(2), and that there are two almost equal possibilities for the hydride and the hydrogen atom transfers from HEH. Examination of the two sets of the (C4-H)(.+) bond dissociation energies shows that the homolytic (C4-H)(.+) bond dissociation energies are much larger than the corresponding heterolytic (C4-H)(.+) bond dissociation energies for the ten NADH models by 23.3-34.4 kcal mol(-1); this suggests that if the hydride transfer from the NADH models is initiated by a one-electron transfer, the proton transfer should be more likely to take place than the corresponding hydrogen atom transfer in the second step. In addition, some elusive structural information about the reaction intermediates of the NADH models was obtained by using Hammett-type linear free-energy analysis. PMID:12584702

Zhu, Xiao-Qing; Li, Hai-Rong; Li, Qian; Ai, Teng; Lu, Jin-Yong; Yang, Yuan; Cheng, Jin-Pei

2003-02-17

199

Accurate dissociation energies of O-H...O hydrogen-bonded 1-naphthol.solvent complexes  

NASA Astrophysics Data System (ADS)

Accurate O-H...O hydrogen-bond dissociation energies were measured for the supersonic-jet-cooled complexes 1-naphthol.S with S=D2O, ethanol, oxirane, and oxetane. A mass-selective pump-dump-probe method was used, combining stimulated emission pumping with resonant two-photon ionization and ion-dip techniques. The ground-state dissociation energies D0(S0) are 5.83+/-0.13 kcal/mol for d1-1-naphthol.D2O, 7.94+/-0.02 kcal/mol for 1-naphthol.ethanol, 7.71+/-0.14 kcal/mol for 1-naphthol.oxirane and >8.17 kcal/mol for 1-naphthol.oxetane. The D0's increase by 5%-7% upon excitation of 1-naphthol to the S1 state. These dissociation energies are compared to those of the analogous complexes with S=H2O, methanol, NH3, and ND3 [Chem. Phys. Lett. 246, 291 (1996)]. The trends in D0 are compared to the electric dipole moments ?, molecular polarizabilities ?, and gas-phase proton affinities of the H bond acceptor molecules. For the O-containing acceptors, the D0's correlate well with ?, but the only good overall correlation for both O- and N-containing acceptors was found between the dissociation energies and proton affinities.

Wickleder, Claudia; Henseler, Debora; Leutwyler, Samuel

2002-02-01

200

Unusually long, multicenter, cation(?+)···anion(?-) bonding observed for several polymorphs of [TTF][TCNE].  

PubMed

The ?, ?, and ? polymorphs of [TTF][TCNE] (TTF=tetrathiafulvalene; TCNE=tetracyanoethylene) exhibit a new type of long, multicenter bonding between the [TTF](?+) and [TCNE](?-) moieties, demonstrating the existence of long, hetero-multicenter bonding with a cationic(?+)···anionic(?-) zwitterionic-like structure. These diamagnetic ?-[TTF](?+) [TCNE](?-) heterodimers exhibit a transfer of about 0.5 e(-) from the TTF to the TCNE fragments, as observed from experimental studies, in accord with theoretical predictions, that is, [TTF(?+)···TCNE(?-)] (??0.5). They have several interfragment distances <3.4 Å, and a computed interaction energy of -21.2 kcal mol(-1), which is typical of long, multicenter bonds. The lower stability of [TTF](?+) [TCNE](?-) with respect to typical ionic bonds is due, in part, to the partial electron transfer that reduces the electrostatic bonding component. This reduced electrostatic interaction, and the large interfragment dispersion stabilize the long, heterocationic/anionic multicenter interaction, which in [TTF(?+)···TCNE(?-)] always involves two electrons, but have ten, eight, and eight bond critical points (bcps) involving C-C, N-S, and sometimes C-S and C-N components for the ?, ?, and ? polymorphs, respectively. In contrast, ?-[TTF][TCNE] possesses [TTF](2)(2+) and [TCNE](2)(2-) dimers, each with long, homo-multicenter 2e(-)/12c (c=center, 2?C+4?S) [TTF](2)(2+) cationic(+)···cationic(+) bonds, as well as long, homo-multicenter 2e(-)/4c [TCNE](2)(2-) anionic(-)···anionic(-) bonding. The MO diagrams for the ?, ?, and ? polymorphs have all of the features found for conventional covalent C-C bonds, and for all of the previously studied multicenter long bonds, for example, ?-[TTF](2)(2+) and ?-[TCNE](2)(2-). The HOMOs for ?-, ?-, and ?-[TTF][TCNE] have 2c C-S and 3c C-C-C orbital-overlap contributions between the [TTF](?+-) and [TCNE](?-) moieties; these are the shortest intra [TTF···TCNE] separations. Thus, from an orbital-overlap perspective, the bonding has 2c and 3c components residing over one S and four C atoms. PMID:21793061

Capdevila-Cortada, Marçal; Novoa, Juan J; Bell, Joshua D; Moore, Curtis E; Rheingold, Arnold L; Miller, Joel S

2011-08-16

201

Carbon K-shell electron energy loss spectra of 1- and 2-butenes, trans-1,3-butadiene, and perfluoro-2-butene. Carbon--carbon bond lengths from continuum shape resonances  

SciTech Connect

Electron energy loss spectra of 1-butene, cis-2-butene, trans-2-butene, trans-1,3-butadiene, and perfluoro-2-butene in the region of carbon K-shell (C 1s) excitation and ionization have been recorded under dipole-dominated inelastic electron scattering conditions. The features observed below the C 1s I.P. in the spectra of the butenes and butadiene are assigned to promotions of C 1s electrons to unoccupied valence (..pi..*) and Rydberg orbitals while broad features observed above the edge are assigned to sigma(C--C) and sigma(C--C) shape resonances. These spectra, along with carbon K-shell spectra of other hydrocarbons, are used to demonstrate that there is a quantitative relationship between carbon--carbon bond lengths and the location of sigma shape resonances relative to the C 1s ionization threshold (I.P.). The C 1s spectrum of perfluoro-2-butene demonstrates dramatic potential barrier effects, namely suppression of Rydberg transitions and strong enhancement of sigma(C--C) and sigma(C--F) shape resonances in the region of the C 1s ionization threshold.

Hitchcock, A.P.; Beaulieu, S.; Steel, T.; Stoehr, J.; Sette, F.

1984-05-01

202

Energy decomposition analysis of the chemical bond in main group and transition metal compounds.  

PubMed

The nature of the chemical bond in the main group diborane(4) compounds X2B-BX2 (X = H,F,Cl,Br,I) and in the Fischer- and Schrock-type transition metal carbene and carbyne complexes and heavier homologues (CO)5W-CH2, (CO)5W-E(OH)2, Cl4W-EH2, Cl(CO)4W-EH and Cl3W-EH (E = C,Si,Ge,Sn,Pb) have been investigated with an energy decomposition analysis (EDA). The results give a deep insight into the nature of the chemical interactions. The EDA results can be used as a bridge between the heuristic models of experimental chemists which have been proven as useful ordering schemes for experimental observations and the physical mechanism which leads to a chemical bond. At the time the data give a well defined qantitative answer to the questions about the strength of the covalent and electrostatic interactions and about the contributions of sigma and pi electrons to the covalent bond. PMID:14527226

Lein, Matthias; Szabó, Andrea; Kovács, Attila; Frenking, Gernot

2003-01-01

203

C\\/C composite oxidation model  

Microsoft Academic Search

A model of the oxidation behaviour of C\\/C composites was developed. The purpose of the model is to predict the carbon loss that occurs at the outer surface and within the porosity of the composite. It takes into account the transport of species in the material, chemical gas–gas and gas–solid reactions, the interaction of both transport phenomena and chemistry, the

M.-P Bacos; J.-M Dorvaux; O Lavigne; Y Renollet

2000-01-01

204

Bond dissociation free energy as a general parameter for flavonoid radical scavenging activity.  

PubMed

Notwithstanding multiple mechanisms of radical scavenging (RS), measured RS activities (RSA) of flavonoids are usually related to O-H bond dissociation enthalpy (BDE) for hydrogen atom transfer (HAT). For 12 flavonoids the reaction free energies were calculated for: (1) HAT, (2) single electron transfer-proton transfer (SET-PT) and (3) sequential proton loss electron transfer (SPLET) in gas and aqueous phases. Aqueous free energies, like bond dissociation (BDFEaq), ionisation (IFEaq) and deprotonation (?Gdeprot,aq) free energies were estimated using thermochemical cycles. While in gas HAT is a RS mechanism (BDFEg

Stepani?, Višnja; Gall Trošelj, Koraljka; Lu?i?, Bono; Markovi?, Zoran; Ami?, Dragan

2013-11-15

205

Guided ion beam and theoretical studies of sequential bond energies of water to sodium cysteine cation.  

PubMed

Absolute bond dissociation energies of water to sodium cysteine (Cys) cations and cysteine to hydrated sodium cations are determined experimentally by collision-induced dissociation of Na(+)Cys(H(2)O)(x), where x = 1-4, complexes with xenon in a guided ion beam mass spectrometer. Experimental results show that the binding energies of water and cysteine to the complexes decrease monotonically with increasing number of water molecules. Quantum chemical calculations at three different levels show reasonable agreement with the experimental bond energies. The calculations indicate that the primary binding site for Na(+) changes from charge-solvated tridentate chelation at the amino nitrogen, carbonyl oxygen, and sulfur side-chain for x = 0 and 1 to the C terminus of zwitterionic cysteine for x = 4, whereas different levels of theory provide conflicting predictions for x = 2 and 3. The first solvent shell of Na(+)Cys is found to be complete at four waters. This is fewer than needed for the aliphatic amino acid glycine, because the functionalized side-chain of Cys provides an internal solvation site, a binding motif that probably applies for most other functionalized amino acids. PMID:20607166

Ye, Sha Joshua; Armentrout, P B

2010-11-01

206

Calculation of bond dissociation energies for large molecules using locally dense basis sets  

NASA Astrophysics Data System (ADS)

A method is given for the calculation of gas-phase bond dissociation energies (BDEs) for relatively large molecules. The method combines the use of locally dense basis sets (LDBS) with density functional theory, using the B3LYP functional. For water and propene, primary and secondary regions are defined and the BDE is tested for consistency with respect to full (primary basis) calculations. Results obtained with LDBS closely approach the limit of using large basis sets throughout. An application of biochemical interest is the determination of the O-H BDE of ?-tocopherol, which contains 81 atoms.

DiLabio, G. A.; Wright, J. S.

1998-11-01

207

Rotational Energy Barrier of the Polarized Carbon–Carbon Double Bond in Quinophthalone  

Microsoft Academic Search

Summary.  ?A dynamic NMR effect is observed in the 13C NMR spectra of anhydrous quinophthalone (quinoline yellow) and its monohydrate in the vicinity of 47°C and 0°C, respectively,\\u000a and is attributed to a restricted rotation around the polarized carbon–carbon double bond. The free energy of activation for\\u000a this process in anhydrous quinophthalone and the monohydrate is 65±2 and 55±2?kJ?·?mol?1, respectively, in

Issa Yavari; Mehdi Adib; Hamid R. Bijanzadeh; Majid M. M. Sadegi; Hossein Logmani-Khouzani; Javad Safari

2002-01-01

208

Comparison of DFT with Traditional Methods for the Calculation of Vibrational Frequencies and Bond Energies  

NASA Technical Reports Server (NTRS)

The vibrational frequencies of MO2 are computed at many levels of theory, including HF, B3LYP, BP86, CASSCF, MP2, and CCSD(T). The computed results are compared with the available experimental results. Most of the methods fail for at least one state of the systems considered. The accuracy of the results and the origin of the observed failures are discussed. The B3LYP bond energies are compared with traditional methods for a variety of systems, ranging from FeCOn+ to SiCln and its positive ions. The cases where B3LYP differs from the traditional methods are discussed.

Bauschlicher, Charles W.; Arnold, James O. (Technical Monitor)

1997-01-01

209

Energy and critical ionic-bond parameter of a 3D large-radius bipolaron  

SciTech Connect

A theory of a strong-coupling large-radius bipolaron has been developed. The possibility of the formation of 3D bipolarons in high-temperature superconductors is discussed. For the bipolaron energy, the lowest variational estimate has been obtained at {alpha} > 8, where {alpha} is the electron-phonon coupling constant. The critical ionic-bond parameter {eta}{sub c} = {epsilon}{sub {infinity}/{epsilon}0}, where {epsilon}{sub {infinity}} and {epsilon}{sub 0} are the high-frequency and static dielectric constants, has been found to be {eta}{sub c} = 0.2496.

Lakhno, V. D., E-mail: lak@impb.psn.r [Russian Academy of Sciences, Institute of Mathematical Problems of Biology (Russian Federation)

2010-05-15

210

Cation-ether complexes in the gas phase: Bond dissociation energies of Na{sup +}(dimethyl ether){sub x}, x = 1-4; Na{sup +}(1,2-dimethoxyethane){sub x}, x = 1 and 2; and Na{sup +}(12-crown-4)  

SciTech Connect

Bond dissociation energies of Na{sup +}[O(CH{sub 3}){sub 2}]{sub x}, x = 1-4; Na{sup +}[(CH{sub 2}OCH{sub 3}){sub 2}]{sub x}, x = 1 and 2; and Na{sup +}[c-(C{sub 2}H{sub 4}O){sub 4}] are reported. The bond dissociation energies are determined experimentally by analysis of the thresholds for collision-induced dissociation of the cation-ether complexes by xenon measured using guided ion beam mass spectrometry. In all cases, the primary and lowest energy dissociation channel observed experimentally is endothermic loss of one ligand molecule. The cross section thresholds are interpreted to yield 0 and 298 K bond dissociation energies after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and unimolecular decay rates. Trends in the bond dissociation energies determined by experiment and recent theoretical ab initio calculations are in good agreement. Our best experimental values, which have an average uncertainty of {+-}7 kJ/mol, are lower than the theoretical values by 7 {+-} 5 kJ/mol per metal-oxygen interaction. These values are compared with bond dissociation energies for the comparable lithium cation-ether complexes. This comparison reveals the thermodynamic consequences of ligand-ligand repulsion. 51 refs., 5 figs., 4 tabs.

More, M.B.; Armentrout, P.B. [Univ. of Utah, Salt Lake City, UT (United States)] [Univ. of Utah, Salt Lake City, UT (United States); Ray, D. [Pacific Northwest National Lab., Richland, WA (United States)] [Pacific Northwest National Lab., Richland, WA (United States)

1997-01-30

211

Sequential bond energies of Pt +(NH 3) x ( x=1–4) determined by collision-induced dissociation and theory  

Microsoft Academic Search

The sequential bond energies of Pt+(NH3)x (x=1–4) are determined by collision-induced dissociation (CID) with Xe using guided-ion beam tandem mass spectrometry. Analysis of the kinetic energy-dependent cross sections includes consideration of multiple ion–neutral collisions, the internal energies of the complexes, and the dissociation lifetimes. We obtain the following 0K bond energies in eV (kJ\\/mol): 2.84±0.12 (274±12), 2.71±0.10 (261±10), 0.80±0.05 (77±5),

R. Liyanage; M. L. Styles; R. A. J. O’Hair; P. B. Armentrout

2003-01-01

212

Evaluating interaction energies of weakly bonded systems using the Buckingham-Hirshfeld method  

NASA Astrophysics Data System (ADS)

We present the finalized Buckingham-Hirshfeld method (BHD-DFT) for the evaluation of interaction energies of non-bonded dimers with Density Functional Theory (DFT). In the method, dispersion energies are evaluated from static multipole polarizabilities, obtained on-the-fly from Coupled Perturbed Kohn-Sham calculations and partitioned into diatomic contributions using the iterative Hirshfeld partitioning method. The dispersion energy expression is distributed over four atoms and has therefore a higher delocalized character compared to the standard pairwise expressions. Additionally, full multipolar polarizability tensors are used as opposed to effective polarizabilities, allowing to retain the anisotropic character at no additional computational cost. A density dependent damping function for the BLYP, PBE, BP86, B3LYP, and PBE0 functionals has been implemented, containing two global parameters which were fitted to interaction energies and geometries of a selected number of dimers using a bi-variate RMS fit. The method is benchmarked against the S22 and S66 data sets for equilibrium geometries and the S22x5 and S66x8 data sets for interaction energies around the equilibrium geometry. Best results are achieved using the B3LYP functional with mean average deviation values of 0.30 and 0.24 kcal/mol for the S22 and S66 data sets, respectively. This situates the BHD-DFT method among the best performing dispersion inclusive DFT methods. Effect of counterpoise correction on DFT energies is discussed.

Krishtal, A.; Van Alsenoy, C.; Geerlings, P.

2014-05-01

213

Evaluating interaction energies of weakly bonded systems using the Buckingham-Hirshfeld method.  

PubMed

We present the finalized Buckingham-Hirshfeld method (BHD-DFT) for the evaluation of interaction energies of non-bonded dimers with Density Functional Theory (DFT). In the method, dispersion energies are evaluated from static multipole polarizabilities, obtained on-the-fly from Coupled Perturbed Kohn-Sham calculations and partitioned into diatomic contributions using the iterative Hirshfeld partitioning method. The dispersion energy expression is distributed over four atoms and has therefore a higher delocalized character compared to the standard pairwise expressions. Additionally, full multipolar polarizability tensors are used as opposed to effective polarizabilities, allowing to retain the anisotropic character at no additional computational cost. A density dependent damping function for the BLYP, PBE, BP86, B3LYP, and PBE0 functionals has been implemented, containing two global parameters which were fitted to interaction energies and geometries of a selected number of dimers using a bi-variate RMS fit. The method is benchmarked against the S22 and S66 data sets for equilibrium geometries and the S22x5 and S66x8 data sets for interaction energies around the equilibrium geometry. Best results are achieved using the B3LYP functional with mean average deviation values of 0.30 and 0.24 kcal/mol for the S22 and S66 data sets, respectively. This situates the BHD-DFT method among the best performing dispersion inclusive DFT methods. Effect of counterpoise correction on DFT energies is discussed. PMID:24832251

Krishtal, A; Van Alsenoy, C; Geerlings, P

2014-05-14

214

Trends in bond dissociation energies of alcohols and aldehydes computed with multireference averaged coupled-pair functional theory.  

PubMed

As part of our ongoing investigation of the combustion chemistry of oxygenated molecules using multireference correlated wave function methods, we report bond dissociation energies (BDEs) in C1-C4 alcohols (from methanol to the four isomers of butanol) and C1-C4 aldehydes (from methanal to butanal). The BDEs are calculated with a multireference averaged coupled-pair functional-based scheme. We compare these multireference BDEs with those derived from experiment and single-reference methods. Trends in BDEs for the alcohols and aldehydes are rationalized by considering geometry relaxations of dissociated radical fragments, resonance stabilization, and hyperconjugation. Lastly, we discuss the conjectured association between bond strengths and rates of hydrogen abstraction by hydroxyl radicals. In general, abstraction reaction rates are higher at sites where the C-H bond energies are lower (and vice versa). However, comparison with available rate data shows this inverse relationship between bond strengths and abstraction rates does not hold at all temperatures. PMID:24708179

Oyeyemi, Victor B; Keith, John A; Carter, Emily A

2014-05-01

215

On the dissociation energies and bonding in NiCO + and TiCO +  

NASA Astrophysics Data System (ADS)

Ab initio calculations on the NiCO + and TiCO + molecules are carried out using large Gaussian basis sets and extensive treatment of electron correlation. The NiCO + molecule is found to have a 2? + ground state with a 2? state only 2.1 kcal/mole higher in energy. The 4? and 4? states of TiCO + are almost degenerate, but the 4? state has a substantially greater bond length due to a larger contribution from the Ti + (3d 24s 1) occupation. The Ni +-CO structure is about 11 and 28 kcal/mole more stable than the Ni +-OC and the T-shaped structures, respectively. The dissociation energy De of the Ni +-CO structure is computed to be 34.3 kcal/mole, suggesting that the experimental value of 48±2 kal/mole is substantially too large. The corresponding De of TiCO + is 28 kcal/mole.

Bauschlicher, Charles W.; Barnes, Leslie A.

1988-09-01

216

Bridging the momentum distribution and the potential energy surface of protons in hydrogen bonds  

NASA Astrophysics Data System (ADS)

Open path integral Car-Parrinello molecular dynamics studies have uncovered the proton momentum distribution in various phases of ice [1,2]. These systems exhibit a wide range of behavior, including symmetric hydrogen bonds and quantum tunneling. In this work, we provide an in-depth statistical analysis of the simulation results. This analysis reveals a direct relation between the open path formalism of quantum particles and their underlying potential energy surface. Application of this analysis to ice systems provides quantitative information about the principle axes of the potential energy surface that the proton experiences, and indicates that the oxygen-oxygen distance is a proper reaction coordinate for such systems. Our analysis also facilitates a direct observation of anharmonic effects along the principle axes. [1] J. A. Morrone and R. Car, Phys. Rev. Lett. 101, 17801, 2008. [2] J. A. Morrone, L. Lin and R. Car, J. Chem. Phys. 130, 204511, 2009.

Morrone, Joseph; Lin, Lin; Car, Roberto; Parrinello, Michele

2010-03-01

217

Overcoming lability of extremely long alkane carbon-carbon bonds through dispersion forces.  

PubMed

Steric effects in chemistry are a consequence of the space required to accommodate the atoms and groups within a molecule, and are often thought to be dominated by repulsive forces arising from overlapping electron densities (Pauli repulsion). An appreciation of attractive interactions such as van der Waals forces (which include London dispersion forces) is necessary to understand chemical bonding and reactivity fully. This is evident from, for example, the strongly debated origin of the higher stability of branched alkanes relative to linear alkanes and the possibility of constructing hydrocarbons with extraordinarily long C-C single bonds through steric crowding. Although empirical bond distance/bond strength relationships have been established for C-C bonds (longer C-C bonds have smaller bond dissociation energies), these have no present theoretical basis. Nevertheless, these empirical considerations are fundamental to structural and energetic evaluations in chemistry, as summarized by Pauling as early as 1960 and confirmed more recently. Here we report the preparation of hydrocarbons with extremely long C-C bonds (up to 1.704?Å), the longest such bonds observed so far in alkanes. The prepared compounds are unexpectedly stable--noticeable decomposition occurs only above 200?°C. We prepared the alkanes by coupling nanometre-sized, diamond-like, highly rigid structures known as diamondoids. The extraordinary stability of the coupling products is due to overall attractive dispersion interactions between the intramolecular H•••H contact surfaces, as is evident from density functional theory computations with and without inclusion of dispersion corrections. PMID:21921913

Schreiner, Peter R; Chernish, Lesya V; Gunchenko, Pavel A; Tikhonchuk, Evgeniya Yu; Hausmann, Heike; Serafin, Michael; Schlecht, Sabine; Dahl, Jeremy E P; Carlson, Robert M K; Fokin, Andrey A

2011-09-15

218

Reactions of the allenylidenes trans-[IrCl[=C=C=C(ph)R](PiPr3)2] with electrophiles: generation of butatriene-, carbene-, and carbyne- iridium complexes.  

PubMed

The allenylidenciridium(I) complexes trans-[IrX(=C=C-CPh2)(PiPr3)2] (X = Cl: 1; X = I: 2) react with excess methyl iodide by C-C coupling and elimination of HI to give the eta2-butatriene compounds trans-[IrX-(eta2-CH2=C=C=CPh2)(PiPr3)2] (3, 4), of which 3 (X = Cl) was characterized by X-ray crystallography. Treatment of 1 and 5 (containing C=C=C(Ph)tBu as the allenylidene ligand) with HCI leads to the formation of the six-coordinate hydridoiridium(III) complexes [IrHCl2[= C=C=C(Ph)R](PiPr3)2] (6, 7) by oxidative addition at the metal center. In contrast, the reactions of 1 and 5 with both CF3CO2H and CF3SO3H afford the four-coordinate vinylcarbene compounds trans-[IrCl[=C(X)-CH=C(Ph)R[(PiPr3)2] (8-10). For X= CF3CO2, in nitromethane a dissociation of the C-X bond occurs and the cationic iridium carbynes trans-[IrCl[=C-CH=C(Ph)R](PiPr3)2]+ are generated. Upon addition of NaBPh4, the stable carbyne complexes 11b (R= Ph) and 12b (R = tBu) with BPh4 as the counterion were isolated in almost quantitative yields. The X-ray crystal structure analysis of 6 reveals that the chloro ligands are cis and the phosphane ligands trans disposed. PMID:11757655

Ilg, K; Werner, H

2001-11-01

219

The Pairwise Correlated Generalized Valence Bond Model of Electronic Structure I; The Estimation of Pair Energies from Orbital Overlaps  

PubMed Central

A new method for the accurate a priori calculation of atomic and molecular energies is proposed. The new method agrees with experiment to within less than 1 kcal/mole in all cases examined thus far, and is applicable to excited states and to transition states for chemical reactions. Since the new method corrects the results of generalized valence bond calculations for the effects of electron pair correlations, we call the new method the pairwise correlated generalized valence bond method.

Petersson, G. A.

1974-01-01

220

An alternative energy–size relationship to that proposed by Bond for the design and optimisation of grinding circuits  

Microsoft Academic Search

Despite reservations of a number of researchers concerning the applicability of Bond's equation for relating specific energy to the size reduction of rocks, his approach has become an industry standard.Data from a large number of pilot and full-scale autogenous (AG), semi-autogenous (SAG) and ball mill circuits are used to show that Bond's equation does not hold over the particle size

Stephen Morrell

2004-01-01

221

Periodic trends in transition metal-hydrogen, metal-carbon, and metal-oxygen bond dissociation energies. Correlation with reactivity and electronic structure  

SciTech Connect

Results of ion beam experiments in which an examination of the translational energy dependence of endothermic reactions yielded bond energies for metal hydrides, methyls, carbenes, and oxides are summarized for these compounds of Cr, Mn, Fe, Co, Ni, and Zn. The data indicate a close correlation of metal-ligand bond energies with the electronic configuration of the metal ion. On the basis of the noted correlations, some predictions of bond energies of the other transition metals are made. (BLM)

Armentrout, P.B.; Halle, L.F.; Beauchamp, J.L.

1981-10-21

222

Strong covalent bonding between two graphene layers  

NASA Astrophysics Data System (ADS)

We show that two graphene layers stacked directly on top of each other ( AA stacking) form strong chemical bonds when the distance between planes is 0.156nm . Simultaneously, C-C in-plane bonds are considerably weakened from partial double bond (0.141nm) to single bond (0.154nm) . This polymorphic form of graphene bilayer is metastable with an activation energy of 0.16eV/cell with respect to the standard configuration bound by van der Waals forces at a larger separation between planes (0.335nm) . Carbon atoms form four single bonds in a geometry mixing 90° and 120° angles, intermediate between the usual sp2 and sp3 , but similar to the one found in molecules like the cubane, pentaprismane, or hexaprismane. Under an in-plane stress of 9GPa , this carbon allotrope becomes the global energy minimum. As a function of the separation between layers, the electronic band structure goes through different regimes: It is a semimetal at van der Waals-like distances, a wide gap semiconductor at covalentlike distances, and in between it displays metallic behavior.

de Andres, P. L.; Ramírez, R.; Vergés, J. A.

2008-01-01

223

Evaluation by Rocket Combustor of C/C Composite Cooled Structure Using Metallic Cooling Tubes  

NASA Astrophysics Data System (ADS)

In this study, the cooling performance of a C/C composite material structure with metallic cooling tubes fixed by elastic force without chemical bonding was evaluated experimentally using combustion gas in a rocket combustor. The C/C composite chamber was covered by a stainless steel outer shell to maintain its airtightness. Gaseous hydrogen as a fuel and gaseous oxygen as an oxidizer were used for the heating test. The surface of these C/C composites was maintained below 1500 K when the combustion gas temperature was about 2800 K and the heat flux to the combustion chamber wall was about 9 MW/m2. No thermal damage was observed on the stainless steel tubes that were in contact with the C/C composite materials. The results of the heating test showed that such a metallic tube-cooled C/C composite structure is able to control the surface temperature as a cooling structure (also as a heat exchanger) as well as indicated the possibility of reducing the amount of coolant even if the thermal load to the engine is high. Thus, application of this metallic tube-cooled C/C composite structure to reusable engines such as a rocket-ramjet combined-cycle engine is expected.

Takegoshi, Masao; Ono, Fumiei; Ueda, Shuichi; Saito, Toshihito; Hayasaka, Osamu

224

Densification Behavior and Performances of C/C Composites Derived from Various Carbon Matrix Precursors  

NASA Astrophysics Data System (ADS)

Three types of carbon/carbon (C/C) composites were manufactured by densifying the needled carbon fiber preform through resin and pitch impregnation/carbonization repeatedly, as well as propylene pyrolysis by chemical vapor infiltration plus carbonization after the resin impregnation/carbonization. The densification behavior and performances (involving electric, thermal, and mechanical properties, as well as impurity) of the C/C composites were investigated systematically. The results show that besides the processing and testing conditions, the electric resistivity, thermal conductivity (TC), coefficient of thermal expansion (CTE), strength, and fracture, as well as impurity content and composition of the C/C composites were closely related to the fiber orientation, interfacial bonding between carbon fiber and carbon matrix, material characteristics of the three precursors and the resulting matrix carbons. In particular, the resin-carbon matrix C/C (RC/C) composites had the highest electric resistivity, tensile, and flexural strength, as well as impurity content. Meanwhile, the pitch-carbon matrix C/C (PC/C) composites possessed the highest TC and CTE in the parallel and vertical direction. And most of the performances of pyro-carbon/resin carbon matrix C/C composites were between those of the RC/C and PC/C composites except the impurity content.

Shao, H. C.; Xia, H. Y.; Liu, G. W.; Qiao, G. J.; Xiao, Z. C.; Su, J. M.; Zhang, X. H.; Li, Y. J.

2014-01-01

225

Bond dissociation energies of organophosphorus compounds: an assessment of contemporary ab initio procedures.  

PubMed

Thermodynamic properties of phosphorus-containing compounds were investigated using high-level ab initio computations. An extended set of contemporary density functional theory (DFT) procedures was assessed for their ability to accurately predict bond dissociation energies of a set of phosphoranyl radicals. The results of meta- and double-hybrids as well as more recent methods, in particular M05, M05-2X, M06, and M06-2X, were compared with benchmark G3(MP2)-RAD values. Standard heats of formation, entropies, and heat capacities of a set of ten organophosphorus compounds were determined and the low-cost BMK functional was found to provide results consistent with available experimental data. In addition, bond dissociation enthalpies (BDEs) were computed using the BMK, M05-2X, and SCS-ROMP2 procedure. The three methods give the same stability trend. The BDEs of the phosphorus(III) molecules were found to be lower than their phosphorus(V) counterparts. Overall, the following ordering is found: BDE(P-OPh) < BDE(P-CH(3)) < BDE(P-Ph) < BDE(P-OCH(3)). PMID:20141194

Hemelsoet, Karen; Van Durme, Frederick; Van Speybroeck, Veronique; Reyniers, Marie-Françoise; Waroquier, Michel

2010-03-01

226

Enthalpies of formation, bond dissociation energies, and molecular structures of the n-aldehydes (acetaldehyde, propanal, butanal, pentanal, hexanal, and heptanal) and their radicals.  

PubMed

Aldehydes are important intermediates and products in a variety of combustion and gas-phase oxidation processes, such as in low-temperature combustion, in the atmosphere, and in interstellar media. Despite their importance, the enthalpies of formation and bond dissociation energies (BDEs) for the aldehydes are not accurately known. We have determined enthalpies of formation for acetaldehyde, propanal, and butanal from thermodynamic cycles, using experimentally measured reaction and formation enthalpies. All enthalpy values used for reference molecules and reactions were first verified to be accurate to within around 1 kcal mol-1 using high-level ab initio calculations. Enthalpies of formation were found to be -39.72 +/- 0.16 kcal mol-1 for acetaldehyde, -45.18 +/- 1.1 kcal mol-1 for propanal, and -49.27 +/- 0.16 kcal mol-1 for butanal. Enthalpies of formation for these three aldehydes, as well as for pentanal, hexanal, and heptanal, were calculated using the G3, G3B3, and CBS-APNO theoretical methods, in conjunction with bond-isodesmic work reactions. On the basis of the results of our thermodynamic cycles, theoretical calculations using isodesmic work reactions, and existing experimental measurements, we suggest that the best available formation enthalpies for the aldehydes acetaldehyde, propanal, butanal, pentanal, hexanal, and heptanal are -39.72, -45.18, -50.0, -54.61, -59.37, and -64.2 kcal mol-1, respectively. Our calculations also identify that the literature enthalpy of formation of crotonaldehyde is in error by as much as 1 kcal mol-1, and we suggest a value of -25.1 kcal mol-1, which we calculate using isodesmic work reactions. Bond energies for each of the bonds in the aldehydes up to pentanal were calculated at the CBS-APNO level. Analysis of the BDEs reveals the R-CH(2)CH=O to be the weakest bond in all aldehydes larger than acetaldehyde, due to formation of the resonantly stabilized vinoxy radical (vinyloxy radical/formyl methyl radical). It is proposed that the vinoxy radical as well as the more commonly considered formyl and acetyl radicals are important products of aldehyde combustion and oxidation, and the reaction pathways of the vinoxy, formyl, and acetyl radicals are discussed. Group additivity values for the carbon-oxygen-hydrogen groups common to the aldehydes are also determined. Internal rotor profiles and electrostatic potential surfaces are used to study the dipole induced dipole-dipole interaction in the synperiplanar conformation of propanal. It is proposed that the loss of this dipole-dipole interaction in RC(.-)HCH(2)CH=O radicals causes a ca. 1-2 kcal mol-1 decrease in the aldehyde C-H and C-C bond energies corresponding to RC(.-)HCH(2)CH=O radical formation. PMID:17134166

da Silva, Gabriel; Bozzelli, Joseph W

2006-12-01

227

Reaction of scandium ions with ethane. First and second hydride-scandium ion bond energies  

SciTech Connect

Reactions of atomic scandium ions with ethane (d/sub 0/, 1,1,1-d/sub 3/, and d/sub 6/) are examined by using guided ion beam mass spectrometry. The present results for ethane-d/sub 0/ are in qualitative agreement with the previous work of Tolbert and Beauchamp. Although the dominant reaction at low energies is exothermic dehydrogenation, this is inefficient. Strong inter- and intramolecular isotope effects suggest that this inefficiency results from the need for a triplet-singlet surface crossing. At low energies dehydrogenation forms a Sc/sup +/-ethene complex, while at higher energies, the product is Sc/sup +/-ethylidene. Double dehydrogenation of ethane has two components: an exothermic one and an apparent endothermic one. Several possible explanations are discussed for this unusual result. The results are analyzed to yield both the first and second metal hydride bond energies, D/sup 0/ /sub 298/(Sc/sup +/-H) = 56.2 +/- 2 and D/sup 0/ /sub 298/(HSc/sup +/H) = 59.3 +/- 3.7 as well as D/sup 0/ /sub 298/(Sc/sup +/-CH/sub 3/) = 59.0 +/- 3 and D/sup 0/ /sub 298/(Sc/sup +/-CH/sub 2/) greater than or equal to 93.4 +/- 2.5, all in kcal/mol.

Sunderlin, L.; Aristov, N.; Armentrout, P.B.

1987-01-07

228

Influence of warm air-drying on enamel bond strength and surface free-energy of self-etch adhesives.  

PubMed

We examined the effect of warm air-drying on the enamel bond strengths and the surface free-energy of three single-step self-etch adhesives. Bovine mandibular incisors were mounted in self-curing resin and then wet ground with #600 silicon carbide (SiC) paper. The adhesives were applied according to the instructions of the respective manufacturers and then dried in a stream of normal (23°C) or warm (37°C) air for 5, 10, and 20 s. After visible-light irradiation of the adhesives, resin composites were condensed into a mold and polymerized. Ten samples per test group were stored in distilled water at 37°C for 24 h and then the bond strengths were measured. The surface free-energies were determined by measuring the contact angles of three test liquids placed on the cured adhesives. The enamel bond strengths varied according to the air-drying time and ranged from 15.8 to 19.1 MPa. The trends for the bond strengths were different among the materials. The value of the ?S? component increased slightly when drying was performed with a stream of warm air, whereas that of the ?S? component decreased significantly. These data suggest that warm air-drying is essential to obtain adequate enamel bond strengths, although increasing the drying time did not significantly influence the bond strength. PMID:23841790

Shiratsuchi, Koji; Tsujimoto, Akimasa; Takamizawa, Toshiki; Furuichi, Tetsuya; Tsubota, Keishi; Kurokawa, Hiroyasu; Miyazaki, Masashi

2013-08-01

229

Changes in energy of three types of hydrogen bonds upon excitation of aminocoumarins determined from absorption solvatochromic experiments.  

PubMed

Absorption spectra of 6-aminocoumarin (6AC) and 7-aminocoumarins (C120 and C151) were studied in polyfluorinated alcohols: (1,1,1,3,3,3-hexafluoroisopropanol (HFIP), 2,2,2-trifluoroethanol (TFE)), in water and in methanol, and compared to those taken in 1-chloro-n-alkanes. According to our results, the observed unusual blue-shift of a long-wavelength band in absorption spectra in strong protic solvents is direct evidence of significant weakening of a NH-O hydrogen bond. The results obtained for the aminocoumarins in HFIP, which in contrast to aliphatic alcohols does not form hydrogen bonds of the acceptor type, prove that the decrease in the energy of the NH-O hydrogen bond upon excitation to the lowest S(1)-LE state is significantly greater than the increase in the energy of hydrogen bonds made by the oxygen atom of carbonyl group OH-O. It is in contrast to theoretical calculations for C151 [Y. Liu, J. Ding, R. Liu, D. Shi and J. Sun, J. Photochem. Photobiol. A, 2009, 201, 203-207]. A comparison of the absorption spectra measured in DMSO and in 1-chloro-n-alkanes shows that the energy of two N-HO hydrogen bonds considerably increases as a result of excitation. These results are consistent with those of the theoretical calculations [Y. Liu, J. Ding, R. Liu, D. Shi and J. Sun, J. Photochem. Photobiol. A, 2009, 201, 203-207; P. Zhou, P. Song, J. Liu, K. Han and G. He, Phys. Chem. Chem. Phys., 2009, 11, 9440-9449]. In this study we applied the procedure proposed by us in J. Photochem. Photobiol. A, 2006, 184, 250-264 for the determination of changes in hydrogen bond energy as a result of electronic excitation based on analysis of the absorption spectra of the probe studied in the solvents interacting with it exclusively nonspecifically and in those forming hydrogen bonds with it. PMID:21566823

Krystkowiak, Ewa; Maciejewski, Andrzej

2011-06-21

230

Observation of the decay ?(3686)???¯±??+c.c.  

NASA Astrophysics Data System (ADS)

Using a sample of 1.06×108 ?(3686) events collected with the BESIII detector, we present the first observation of the decays of ?(3686)???¯+?-+c.c. and ?(3686)???¯-?++c.c. The branching fractions are measured to be B(?(3686)???¯+?-+c.c.)=(1.40±0.03±0.13)×10-4 and B(?(3686)???¯-?++c.c.)=(1.54±0.04±0.13)×10-4, where the first errors are statistical and the second ones systematic.

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Ambrose, D. J.; An, F. F.; An, Q.; Bai, J. Z.; Baldini Ferroli, R.; Ban, Y.; Bennett, J. V.; Bertani, M.; Bian, J. M.; Boger, E.; Bondarenko, O.; Boyko, I.; Braun, S.; Briere, R. A.; Cai, H.; Cai, X.; Cakir, O.; Calcaterra, A.; Cao, G. F.; Cetin, S. A.; Chang, J. F.; Chelkov, G.; Chen, G.; Chen, H. S.; Chen, J. C.; Chen, M. L.; Chen, S. J.; Chen, X.; Chen, X. R.; Chen, Y. B.; Cheng, H. P.; Chu, X. K.; Chu, Y. P.; Cronin-Hennessy, D.; Dai, H. L.; Dai, J. P.; Dedovich, D.; Deng, Z. Y.; Denig, A.; Denysenko, I.; Destefanis, M.; Ding, W. M.; Ding, Y.; Dong, C.; Dong, J.; Dong, L. Y.; Dong, M. Y.; Du, S. X.; Fang, J.; Fang, S. S.; Fang, Y.; Fava, L.; Feng, C. Q.; Fu, C. D.; Fu, J. L.; Fuks, O.; Gao, Q.; Gao, Y.; Geng, C.; Goetzen, K.; Gong, W. X.; Gradl, W.; Greco, M.; Gu, M. H.; Gu, Y. T.; Guan, Y. H.; Guo, A. Q.; Guo, L. B.; Guo, T.; Guo, Y. P.; Guo, Y. P.; Han, Y. L.; Harris, F. A.; He, K. L.; He, M.; He, Z. Y.; Held, T.; Heng, Y. K.; Hou, Z. L.; Hu, C.; Hu, H. M.; Hu, J. F.; Hu, T.; Huang, G. M.; Huang, G. S.; Huang, J. S.; Huang, L.; Huang, X. T.; Hussain, T.; Ji, C. S.; Ji, Q.; Ji, Q. P.; Ji, X. B.; Ji, X. L.; Jiang, L. L.; Jiang, X. S.; Jiao, J. B.; Jiao, Z.; Jin, D. P.; Jin, S.; Jing, F. F.; Johansson, T.; Kalantar-Nayestanaki, N.; Kang, X. L.; Kavatsyuk, M.; Kloss, B.; Kopf, B.; Kornicer, M.; Kuehn, W.; Kupsc, A.; Lai, W.; Lange, J. S.; Lara, M.; Larin, P.; Leyhe, M.; Li, C. H.; Li, Cheng; Li, Cui; Li, D.; Li, D. M.; Li, F.; Li, G.; Li, H. B.; Li, J. C.; Li, K.; Li, K.; Li, Lei; Li, P. R.; Li, Q. J.; Li, T.; Li, W. D.; Li, W. G.; Li, X. L.; Li, X. N.; Li, X. Q.; Li, X. R.; Li, Z. B.; Liang, H.; Liang, Y. F.; Liang, Y. T.; Liao, G. R.; Lin, D. X.; Liu, B. J.; Liu, C. L.; Liu, C. X.; Liu, F. H.; Liu, Fang; Liu, Feng; Liu, H. B.; Liu, H. H.; Liu, H. M.; Liu, J.; Liu, J. P.; Liu, K.; Liu, K. Y.; Liu, P. L.; Liu, Q.; Liu, S. B.; Liu, X.; Liu, Y. B.; Liu, Z. A.; Liu, Zhiqiang; Liu, Zhiqing; Loehner, H.; Lou, X. C.; Lu, G. R.; Lu, H. J.; Lu, H. L.; Lu, J. G.; Lu, X. R.; Lu, Y.; Lu, Y. P.; Luo, C. L.; Luo, M. X.; Luo, T.; Luo, X. L.; Lv, M.; Ma, F. C.; Ma, H. L.; Ma, Q. M.; Ma, S.; Ma, T.; Ma, X. Y.; Maas, F. E.; Maggiora, M.; Malik, Q. A.; Mao, Y. J.; Mao, Z. P.; Messchendorp, J. G.; Min, J.; Min, T. J.; Mitchell, R. E.; Mo, X. H.; Moeini, H.; Morales Morales, C.; Moriya, K.; Muchnoi, N. Yu.; Nefedov, Y.; Nikolaev, I. B.; Ning, Z.; Nisar, S.; Niu, X. Y.; Olsen, S. L.; Ouyang, Q.; Pacetti, S.; Pelizaeus, M.; Peng, H. P.; Peters, K.; Ping, J. L.; Ping, R. G.; Poling, R.; Prencipe, E.; Qi, M.; Qian, S.; Qiao, C. F.; Qin, L. Q.; Qin, X. S.; Qin, Y.; Qin, Z. H.; Qiu, J. F.; Rashid, K. H.; Redmer, C. F.; Ripka, M.; Rong, G.; Ruan, X. D.; Sarantsev, A.; Schoenning, K.; Schumann, S.; Shan, W.; Shao, M.; Shen, C. P.; Shen, X. Y.; Sheng, H. Y.; Shepherd, M. R.; Song, W. M.; Song, X. Y.; Spataro, S.; Spruck, B.; Sun, G. X.; Sun, J. F.; Sun, S. S.; Sun, Y. J.; Sun, Y. Z.; Sun, Z. J.; Sun, Z. T.; Tang, C. J.; Tang, X.; Tapan, I.; Thorndike, E. H.; Toth, D.; Ullrich, M.; Uman, I.; Varner, G. S.; Wang, B.; Wang, D.; Wang, D. Y.; Wang, K.; Wang, L. L.; Wang, L. S.; Wang, M.; Wang, P.; Wang, P. L.; Wang, Q. J.; Wang, S. G.; Wang, W.; Wang, X. F.; Wang, Y. D.; Wang, Y. F.; Wang, Y. Q.; Wang, Z.; Wang, Z. G.; Wang, Z. H.; Wang, Z. Y.; Wei, D. H.; Wei, J. B.; Weidenkaff, P.; Wen, S. P.; Werner, M.; Wiedner, U.; Wolke, M.; Wu, G. G.; Wu, L. H.; Wu, N.; Wu, W.; Wu, Z.; Xia, L. G.; Xia, Y.; Xiao, D.; Xiao, Z. J.; Xie, Y. G.; Xiu, Q. L.; Xu, G. F.; Xu, L.; Xu, Q. J.; Xu, Q. N.; Xu, X. P.; Xue, Z.; Yan, L.; Yan, W. B.; Yan, W. C.; Yan, Y. H.; Yang, H. X.; Yang, Y.; Yang, Y. X.; Ye, H.; Ye, M.; Ye, M. H.; Yu, B. X.; Yu, C. X.; Yu, H. W.; Yu, J. S.; Yu, S. P.; Yuan, C. Z.; Yuan, W. L.; Yuan, Y.; Zafar, A. A.; Zallo, A.; Zang, S. L.; Zeng, Y.; Zhang, B. X.; Zhang, B. Y.; Zhang, C.; Zhang, C. B.; Zhang, C. C.; Zhang, D. H.; Zhang, H. H.; Zhang, H. Y.; Zhang, J. J.; Zhang, J. L.; Zhang, J. Q.; Zhang, J. W.; Zhang, J. Y.; Zhang, J. Z.; Zhang, S. H.; Zhang, X. J.; Zhang, X. Y.; Zhang, Y.; Zhang, Y. H.; Zhang, Z. H.; Zhang, Z. P.; Zhang, Z. Y.; Zhao, G.; Zhao, J. W.; Zhao, Lei; Zhao, Ling; Zhao, M. G.; Zhao, Q.; Zhao, Q. W.; Zhao, S. J.; Zhao, T. C.; Zhao, X. H.; Zhao, Y. B.; Zhao, Z. G.; Zhemchugov, A.; Zheng, B.; Zheng, J. P.; Zheng, Y. H.; Zhong, B.; Zhou, L.; Zhou, Li; Zhou, X.; Zhou, X. K.; Zhou, X. R.; Zhou, X. Y.; Zhu, K.; Zhu, K. J.; Zhu, X. L.; Zhu, Y. C.; Zhu, Y. S.; Zhu, Z. A.; Zhuang, J.; Zou, B. S.; Zou, J. H.

2013-12-01

231

Active Metal Brazing and Characterization of Brazed Joints in C-C and C-SiC Composites to Copper-Clad-Molybdenum System  

NASA Technical Reports Server (NTRS)

Carbon/carbon composites with CVI and resin-derived matrices, and C/SiC composites reinforced with T-300 carbon fibers in a CVI SiC matrix were joined to Cu-clad Mo using two Ag-Cu braze alloys, Cusil-ABA (1.75% Ti) and Ticusil (4.5% Ti). The brazed joints revealed good interfacial bonding, preferential precipitation of Ti at the composite/braze interface, and a tendency toward delamination in resin-derived C/C composite. Extensive braze penetration of the inter-fiber channels in the CVI C/C composites was observed. The Knoop microhardness (HK) distribution across the C/C joints indicated sharp gradients at the interface, and a higher hardness in Ticusil than in Cusil-ABA. For the C/SiC composite to Cu-clad-Mo joints, the effect of composite surface preparation revealed that ground samples did not crack whereas unground samples cracked. Calculated strain energy in brazed joints in both systems is comparable to the strain energy in a number of other ceramic/metal systems. Theoretical predictions of the effective thermal resistance suggest that such joined systems may be promising for thermal management applications.

Singh, M.; Asthana, R.

2008-01-01

232

Effect of ultrasonic energy on nanoscale interfacial structure in copper wire bonding on aluminium pads  

NASA Astrophysics Data System (ADS)

The effect of ultrasonic vibration on nanoscale interfacial structure of thermosonic copper wire bonding on aluminium pads was investigated. It was found that bonding strength was determined by the extent of fragmentation of a native aluminium oxide overlayer (5-10 nm thick) on aluminium pads, forming paths for formation of intermetallic compound CuAl2 in areas of direct contact of bonded metal surfaces. The degree of fracture of the oxide layer was strongly affected by a level of ultrasonic power.

Xu, H.; Liu, C.; Silberschmidt, V. V.; Chen, Z.; Acoff, V. L.

2011-04-01

233

On the Use of a Driven Wedge Test to Acquire Dynamic Fracture Energies of Bonded Beam Specimens  

Microsoft Academic Search

A driven wedge test is used to characterize the mode I fracture resistance of adhesively bonded composite beam specimens over a range of crosshead rates up to 1 m\\/s. The shorter moment arms (between wedge contact and crack tip) significantly reduce inertial effects and stored energy in the debonded adherends, when compared with conventional means of testing double cantilever beam (DCB)

David A. Dillard; David J. Pohlit; George C. Jacob; J. Michael Starbuck; Rakesh K. Kapania

2011-01-01

234

Atom-Bond Pairwise Additive Representation for Halide-Benzene Potential Energy Surfaces: an Ab Initio Validation Study#  

Microsoft Academic Search

The detailed knowledge of the basic aspects of molecular interactions and the representation of the involved potential energy surface in a proper analytical form are of paramount importance either to elucidate the nature of noncovalent interactions or to perform meaningful molecular dynamics simulations. To this aim, a recently developed semiempirical method, formulated in terms of atom\\/ion-molecular bond interactions, has been

Margarita Albertí; Antonio Aguilar; Josep M. Lucas; Fernando Pirani; Cecilia Coletti; Nazzareno Re

2009-01-01

235

Rate-limiting step in the low-energy unimolecular decomposition reaction of Ni+* acetone into Ni+CO + ethane.  

PubMed

Rate constants for the low-energy Ni(+)-assisted C-C bond cleavage reaction of deuterium-labeled acetone have been acquired under jet-cooled conditions in the gas phase. The energies used to initiate the dissociative reactions of the precursor complex ion Ni(+)(d(6)-Ac) are well below that required to cleave C-C sigma-bonds in isolated organic molecules. The rate constants are compared to those acquired previously for the lighter Ni(+)(h(6)-Ac) isotope and result in a substantial kinetic isotope effect (k(H)/k(D) approximately 5.5). Arguments are made that implicate isomerization leading to C-C bond coupling as the rate-limiting step (not C-C sigma-bond activation) in the dissociative reaction. PMID:19877648

Dee, S Jason; Castleberry, Vanessa A; Villarroel, Otsmar J; Laboren, Ivanna E; Frey, Sarah E; Ashley, Daniel; Bellert, Darrin J

2009-12-24

236

Bent Bonds and Multiple Bonds.  

ERIC Educational Resources Information Center

Considers carbon-carbon multiple bonds in terms of Pauling's bent bond model, which allows direct calculation of double and triple bonds from the length of a CC single bond. Lengths of these multiple bonds are estimated from direct measurements on "bent-bond" models constructed of plastic tubing and standard kits. (CS)

Robinson, Edward A.; Gillespie, Ronald J.

1980-01-01

237

Development of a simple mixed-mode fracture test and the resulting fracture energy envelope for an adhesive bond  

Microsoft Academic Search

Characterizing the fracture energy of bonded adhesive joints over a range of mode mixities often requires special fixtures\\u000a or a variety of test configurations. By pairing a tapered and a constant thickness adherend, a hybrid double cantilever beam\\u000a (DCB) specimen is proposed. This asymmetric tapered DCB configuration can be used to determine the fracture energy as a function\\u000a of mode

David A. Dillard

2007-01-01

238

Pd(II)-Catalyzed C-H Activation/C-C Cross-Coupling Reactions: Versatility and Practicality  

PubMed Central

In the past decade, palladium-catalyzed C–H activation/C–C bond forming reactions have emerged as promising new catalytic transformations; however, development in this field is still at an early stage compared to the state of the art in cross-coupling reactions using aryl and alkyl halides. This Review begins with a brief introduction of four extensively investigated modes of catalysis for forming C–C bonds from C–H bonds: Pd(II)/Pd(0), Pd(II)/Pd(IV), Pd(0)/Pd(II)/Pd(IV) and Pd(0)/Pd(II) catalysis. More detailed discussion is then directed towards the recent development of Pd(II)-catalyzed coupling of C–H bonds with organometallic reagents through a Pd(II)/Pd(0) catalytic cycle. Despite much progress made to date, improving the versatility and practicality of this new reaction remains a tremendous challenge.

Chen, Xiao; Engle, Keary M.; Wang, Dong-Hui; Yu, Jin-Quan

2009-01-01

239

Coordination-resolved local bond contraction and electron binding-energy entrapment of Si atomic clusters and solid skins  

NASA Astrophysics Data System (ADS)

Consistency between x-ray photoelectron spectroscopy measurements and density-function theory calculations confirms our bond order-length-strength notation-incorporated tight-binding theory predictions on the quantum entrapment of Si solid skin and atomic clusters. It has been revealed that bond-order deficiency shortens and strengthens the Si-Si bond, which results in the local densification and quantum entrapment of the core and valence electrons. Unifying Si clusters and Si(001) and (111) skins, this mechanism has led to quantification of the 2p binding energy of 96.089 eV for an isolated Si atom, and their bulk shifts of 2.461 eV. Findings evidence the significance of atomic undercoordination that is of great importance to device performance.

Bo, Maolin; Wang, Yan; Huang, Yongli; Zhang, Xi; Zhang, Ting; Li, Can; Sun, Chang Q.

2014-04-01

240

Novel carbon-carbon bond formations for biocatalysis  

PubMed Central

Carbon–carbon bond formation is the key transformation in organic synthesis to set up the carbon backbone of organic molecules. However, only a limited number of enzymatic C–C bond forming reactions have been applied in biocatalytic organic synthesis. Recently, further name reactions have been accomplished for the first time employing enzymes on a preparative scale, for instance the Stetter and Pictet–Spengler reaction or oxidative C–C bond formation. Furthermore, novel enzymatic C–C bond forming reactions have been identified like benzylation of aromatics, intermolecular Diels-Alder or reductive coupling of carbon monoxide.

Resch, Verena; Schrittwieser, Joerg H; Siirola, Elina; Kroutil, Wolfgang

2011-01-01

241

Substituent effect on the energy barrier for ?-bond formation from ?-single-bonded species, singlet 2,2-dialkoxycyclopentane-1,3-diyls  

PubMed Central

Summary Background: Localized singlet diradicals are in general quite short-lived intermediates in processes involving homolytic bond-cleavage and formation reactions. In the past decade, long-lived singlet diradicals have been reported in cyclic systems such as cyclobutane-1,3-diyls and cyclopentane-1,3-diyls. Experimental investigation of the chemistry of singlet diradicals has become possible. The present study explores the substituents and the effect of their substitution pattern at the C(1)–C(3) positions on the lifetime of singlet octahydropentalene-1,3-diyls to understand the role of the substituents on the reactivity of the localized singlet diradicals. Results: A series of singlet 2,2-dialkoxy-1,3-diaryloctahydropentalene-1,3-diyls DR were generated in the photochemical denitrogenation of the corresponding azoalkanes AZ. The ring-closed products CP, i.e., 3,3-dialkoxy-2,4-diphenyltricyclo[3.3.0.02,4]octanes, were quantitatively obtained in the denitrogenation reaction. The first-order decay process (k = 1/?) was observed for the fate of the singlet diradicals DR (?max ? 580–590 nm). The activation parameters, ?H ‡ and ?S ‡, for the ring-closing reaction (?-bond formation process) were determined by the temperature-dependent change of the lifetime. The energy barrier was found to be largely dependent upon the substituents Ar and Ar’. The singlet diradical DRf (Ar = 3,5-dimethoxyphenyl, OCH2Ar’ = OCH2(3,5-dimethoxyphenyl)) was the longest-lived, ?293 = 5394 ± 59 ns, among the diradicals studied here. The lifetime of the parent diradical DR (Ar = Ph, OCH2Ar’ = OCH3) was 299 ± 2 ns at 293 K. Conclusion: The lifetimes of the singlet 1,3-diyls are found to be largely dependent on the substituent pattern of Ar and Ar’ at the C(1)–C(3) positions. Both the enthalpy and entropy effect were found to play crucial roles in increasing the lifetime.

Ye, Jianhuai; Fujiwara, Yoshihisa

2013-01-01

242

Linear ketenimines. Variable structures of C,C-dicyanoketenimines and C,C-bis-sulfonylketenimines.  

PubMed

C,C-dicyanoketenimines 10a-c were generated by flash vacuum thermolysis of ketene N,S-acetals 9a-c or by thermal or photochemical decomposition of alpha-azido-beta-cyanocinnamonitrile 11. In the latter reaction, 3,3-dicyano-2-phenyl-1-azirine 12 is also formed. IR spectroscopy of the keteniminines isolated in Ar matrixes or as neat films, NMR spectroscopy of 10c, and theoretical calculations (B3LYP/6-31G) demonstrate that these ketenimines have variable geometry, being essentially linear along the CCN-R framework in polar media (neat films and solution), but in the gas phase or Ar matrix they are bent, as is usual for ketenimines. Experiments and calculations agree that a single CN substituent as in 13 is not enough to enforce linearity, and sulfonyl groups are less effective that cyano groups in causing linearity. C,C-bis(methylsulfonyl)ketenimines 4-5 and a C-cyano-C-(methylsulfonyl)ketenimine 15 are not linear. The compound p-O2NC6H4N=C=C(COOMe)2 previously reported in the literature is probably somewhat linearized along the CCNR moiety. A computational survey (B3LYP/6-31G) of the inversion barrier at nitrogen indicates that electronegative C-substituents dramatically lower the barrier; this is also true of N-acyl substituents. Increasing polarity causes lower barriers. Although N-alkylbis(methylsulfonyl)ketenimines are not calculated to be linear, the barriers are so low that crystal lattice forces can induce planarity in N-methylbis(methylsulfonyl)ketenimine 3. PMID:11846648

Finnerty, Justin; Mitschke, Ullrich; Wentrup, Curt

2002-02-22

243

A DFT study on the interaction between adsorbed silver on C?? and disulfide bond.  

PubMed

Adsorption of a silver atom on the surface of Buckyball (C??) was investigated using density functional theory (DFT). The Ag atom tends to occupy the bridge site over C--C bond in pentagon-hexagon ring junction with the binding energy of -38.33 kcal mol?¹. The capability of destroying S--S bond by both a single silver atom and the silver atom adsorbed on C?? was also investigated by DFT calculations using dimethyl disulfide as the molecular model. The results of the natural bond orbital (NBO) and population analysis indicate that the cleavage of the S--S bond effectively occurs by the silver atom adsorbed on C??. Since denaturation of disulfide bonds of envelope glycoprotein (gp) 120 is a key step in the prevention of the spread of HIV-1, the development of the proposed study is promised to HIV-1 research field. PMID:23085174

Azizi, Khaled; Sohrabinia, Ali

2012-09-01

244

Presolvated low energy electron attachment to peptide methyl esters in aqueous solution: C-O bond cleavage at 77 K.  

PubMed

In this study, the reactions of presolvated electrons with glycine methyl ester and N-acetylalanylalanine methyl ester (N-aAAMe) are investigated by electron spin resonance (ESR) spectroscopy and DFT calculations. Electrons were produced by ?-irradiation in neutral 7.5 M LiCl-D2O aqueous glasses at low temperatures. For glycine methyl ester, electron addition at 77 K results in both N-terminal deamination to form a glycyl radical and C-O ester bond cleavage to form methyl radicals. For samples of N-acetylalanylalanine methyl ester, electrons are found to add to the peptide bonds at 77 K and cleave the carboxyl ester groups to produce methyl radicals. On annealing to 160 K, electron adducts at the peptide links undergo chain scission to produce alanyl radicals and on further annealing to 170 K ?-carbon peptide backbone radicals are produced by hydrogen abstraction. DFT calculations for electron addition to the methyl ester portion of N-aAAMe show the cleavage reaction is highly favorable (free energy equals to -30.7 kcal/mol) with the kinetic barrier of only 9.9 kcal/mol. A substantial electron affinity of the ester link (38.0 kcal/mol) provides more than sufficient energy to overcome this small barrier. Protonated peptide bond electron adducts also show favorable N-C chain cleavage reactions of -12.7 to -15.5 kcal/mol with a barrier from 7.4 to 10.0 kcal/mol. The substantial adiabatic electron affinity (AEA) of the peptide bond and ester groups provides sufficient energy for the bond dissociation. PMID:23406302

Kheir, Jeanette; Chomicz, Lidia; Engle, Alyson; Rak, Janusz; Sevilla, Michael D

2013-03-14

245

Presolvated Low Energy Electron Attachment to Peptide Methyl esters in Aqueous Solution: C-O Bond Cleavage at 77K  

PubMed Central

In this study, the reactions of presolvated electrons with glycine methyl ester and N-acetylalanylalanine methyl ester (N-aAAMe) are investigated by electron spin resonance (ESR) spectroscopy and DFT calculations. Electrons were produced by gamma irradiation in neutral 7.5 M LiCl-D2O aqueous glasses at low temperatures. For glycine methyl ester electron addition at 77K results in both N-terminal deamination to form a glycyl radical and C-O ester bond cleavage to form methyl radicals. For samples of N-acetylalanylalanine methyl ester electrons are found to add to the peptide bonds at 77K and cleave the carboxyl ester groups to produce methyl radicals. On annealing to 160K electron adducts at the peptide links undergo chain scission to produce alanyl radicals and further annealing to 170K ?-carbon peptide backbone radicals are produced by hydrogen abstraction. DFT calculations for electron addition to the methyl ester portion of N-aAAMe show the cleavage reaction is highly favorable (free energy equals to ?30.7 kcal/mol) with the kinetic barrier of only 9.9 kcal/mol. A substantial electron affinity of the ester link (38.0 kcal/mol) provides more than sufficient energy to overcome this small barrier. Protonated peptide bond electron adducts, also show favorable N-C chain cleavage reactions of ?12.7 to ?15.5 kcal/mol with a barrier from 7.4 to 10.0 kcal/mol. The substantial adiabatic electron affinity (AEA) of the peptide bond and ester groups provides sufficient energy for the bond dissociation.

Kheir, Jeanette; Chomicz, Lidia; Engle, Alyson; Rak, Janusz; Sevilla, Michael D.

2013-01-01

246

Chemical bonding in view of electron charge density and kinetic energy density descriptors.  

PubMed

Stalke's dilemma, stating that different chemical interpretations are obtained when one and the same density is interpreted either by means of natural bond orbital (NBO) and subsequent natural resonance theory (NRT) application or by the quantum theory of atoms in molecules (QTAIM), is reinvestigated. It is shown that within the framework of QTAIM, the question as to whether for a given molecule two atoms are bonded or not is only meaningful in the context of a well-defined reference geometry. The localized-orbital-locator (LOL) is applied to map out patterns in covalent bonding interaction, and produces results that are consistent for a variety of reference geometries. Furthermore, LOL interpretations are in accord with NBO/NRT, and assist in an interpretation in terms of covalent bonding. PMID:19090572

Jacobsen, Heiko

2009-05-01

247

Universal Bronsted-Evans-Polanyi Relations for C-C, C-O, C-N, N-O, N-N, and O-O Dissociation Reactions  

SciTech Connect

It is shown that for all the essential bond forming and bond breaking reactions on metal surfaces, the reactivity of the metal surface correlates linearly with the reaction energy in a single universal relation. Such correlations provide an easy way of establishing trends in reactivity among the different transition metals.

Wang, Shengguang

2010-10-27

248

Using the MMFF94 model to predict structures and energies for hydrogen-bonded urea-anion complexes  

SciTech Connect

The performance of the MMFF94 model has been compared with density functional theory (B3LYP/DZVP2) in calculation of hydrogen-bonded complexes of urea with three different shaped Cl?, NO3?, and ClO4? anions. After modification of selected van der Waals parameters, good agreement between the two methods was obtained for geometric parameters and relative conformational energies. Absolute values of MMFF94 binding energies are under estimated, but application of a systematic correction yields binding energies that are within ?1 kcal/mol of B3LYP/DZVP2 values.

Bryantsev, Vyacheslav; Hay, Benjamin P.

2005-07-11

249

Computational chemistry of the silicon nitride surface. 2. Binary hydroxylamine complexes. Geometry and bond energies  

Microsoft Academic Search

In order to study the silicon nitride surface it is interesting to consider hydrogen-bonded complexes with hydroxyl and amine\\u000a key groups (OH...O, OH...N, NH...O, and NH...N). To investigate the behavior of the above bonds, we considered the water,\\u000a ammonia, and hydroxylamine dimers and the binary hydroxylamine complexes with water and ammonia. The results of this work\\u000a are compared with the

N. V. Goncharova; E. A. Nikitina; V. D. Khavryuchenko; E. F. Sheka

1996-01-01

250

Inferring modules of functionally interacting proteins using the Bond Energy Algorithm  

PubMed Central

Background Non-homology based methods such as phylogenetic profiles are effective for predicting functional relationships between proteins with no considerable sequence or structure similarity. Those methods rely heavily on traditional similarity metrics defined on pairs of phylogenetic patterns. Proteins do not exclusively interact in pairs as the final biological function of a protein in the cellular context is often hold by a group of proteins. In order to accurately infer modules of functionally interacting proteins, the consideration of not only direct but also indirect relationships is required. In this paper, we used the Bond Energy Algorithm (BEA) to predict functionally related groups of proteins. With BEA we create clusters of phylogenetic profiles based on the associations of the surrounding elements of the analyzed data using a metric that considers linked relationships among elements in the data set. Results Using phylogenetic profiles obtained from the Cluster of Orthologous Groups of Proteins (COG) database, we conducted a series of clustering experiments using BEA to predict (upper level) relationships between profiles. We evaluated our results by comparing with COG's functional categories, And even more, with the experimentally determined functional relationships between proteins provided by the DIP and ECOCYC databases. Our results demonstrate that BEA is capable of predicting meaningful modules of functionally related proteins. BEA outperforms traditionally used clustering methods, such as k-means and hierarchical clustering by predicting functional relationships between proteins with higher accuracy. Conclusion This study shows that the linked relationships of phylogenetic profiles obtained by BEA is useful for detecting functional associations between profiles and extending functional modules not found by traditional methods. BEA is capable of detecting relationship among phylogenetic patterns by linking them through a common element shared in a group. Additionally, we discuss how the proposed method may become more powerful if other criteria to classify different levels of protein functional interactions, as gene neighborhood or protein fusion information, is provided.

Watanabe, Ryosuke LA; Morett, Enrique; Vallejo, Edgar E

2008-01-01

251

Is the decrease of the total electron energy density a covalence indicator in hydrogen and halogen bonds?  

PubMed

In this work, halogen bonding (XB) and hydrogen bonding (HB) complexes were studied with the aim of analyzing the variation of the total electronic energy density H(r b ) with the interaction strengthening. The calculations were performed at the MP2/6-311++G(2d,2p) level of approximation. To explain the nature of such interactions, the atoms in molecules theory (AIM) in conjunction with reduced variational space self-consistent field (RVS) energy decomposition analysis were carried out. Based on the local virial theorem, an equation to decompose the total electronic energy density H(r b ) in two energy densities, (-G(r b )) and 1/4?(2)?(r b ), was derived. These energy densities were linked with the RVS interaction energy components. Through the connection between both decomposition schemes, it was possible to conclude that the decrease in H(r b ) with the interaction strengthening observed in the HB as well as the XB complexes, is mainly due to the increase in the attractive electrostatic part of the interaction energy and in lesser extent to the increase in its covalent character, as is commonly considered. PMID:23187685

Angelina, Emilio L; Duarte, Darío J R; Peruchena, Nélida M

2013-05-01

252

Covalent bonds are created by the drive of electron waves to lower their kinetic energy through expansion.  

PubMed

An analysis based on the variation principle shows that in the molecules H2 (+), H2, B2, C2, N2, O2, F2, covalent bonding is driven by the attenuation of the kinetic energy that results from the delocalization of the electronic wave function. For molecular geometries around the equilibrium distance, two features of the wave function contribute to this delocalization: (i) Superposition of atomic orbitals extends the electronic wave function from one atom to two or more atoms; (ii) intra-atomic contraction of the atomic orbitals further increases the inter-atomic delocalization. The inter-atomic kinetic energy lowering that (perhaps counter-intuitively) is a consequence of the intra-atomic contractions drives these contractions (which per se would increase the energy). Since the contractions necessarily encompass both, the intra-atomic kinetic and potential energy changes (which add to a positive total), the fact that the intra-atomic potential energy change renders the total potential binding energy negative does not alter the fact that it is the kinetic delocalization energy that drives the bond formation. PMID:24880263

Schmidt, Michael W; Ivanic, Joseph; Ruedenberg, Klaus

2014-05-28

253

Quantum effects on the structure and energy of a protonated linear chain of hydrogen-bonded water molecules  

Microsoft Academic Search

Computer simulations of a protonated, linear cluster of four hydrogen-bonded water molecules, (O4H9)+, are reported. The potential energy surface governing the motion of the nuclei was described with the polarization model of Stillinger and co-workers. The quantization of all the hydrogen nuclei was treated with the discretized Feynman path integral formalism. Results indicate that quantum dispersion has a significant influence

Régis Pomès; Benoît Roux

1995-01-01

254

Adherence-fracture energy of a glass-bonded thick-film conductor: effect of firing conditions  

Microsoft Academic Search

The effect of firing conditions on the adherence of a glass-bonded Pt-Au printed thick film conductor to a 96 wt % Al2O3 substrate was determined by a fracture mechanics measurement of the critical fracture energy for catastrophic thick film-substrate separation. The technique also demonstrated that separation by slow crack growth (delayed failure) occurred in this system. Analysis of the thick

P. F. Becher; W. L. Newell

1977-01-01

255

Application of density functional theory \\/Hartree-Fock hybrid methods. Geometries and bond dissociation energies of Al + complexes  

Microsoft Academic Search

A mixture of Hartree-Fock exchange and density functional theory exchange-correlation treatment has been applied to determine the geometry and bond dissociation energies (BDEs) of cationic Al+-X complexes (X = CH3, NH3, H2O, OH, HF, HCN, HNC, CO, CN, CH2O, CO2, N2, O2, and F2). By using the local spin density approximation and the ‘Becke-3-Lee-Young-Parr’ functionals each combined with three different

Detlef Stöckigt

1996-01-01

256

Theoretical calculation of bond dissociation energies and heats of formation for nitromethane and polynitromethanes with density functional theory  

NASA Astrophysics Data System (ADS)

The C bond NO2 bond dissociation energies (BDEs) and the heats of formation (HOFs) of nitromethane and polynitromethanes (dinitromethane, trinitromethane, and tetranitromethane) system in gas phase at 298.15 K were calculated theoretically. Density functional theory (DFT) B3LYP, B3P86, B3PW91, and PBE0 methods in combination with different basis sets were employed. It was found that the C bond NO2 bond BDEs can be improved from B3LYP to B3PW91 to B3P86 or PBE0 functional. Levels of theory employing B3P86 and PBE0 functionals were found to be sufficiently reliable without the presence of diffusion functions. As the number of NO2 groups on the same C atom increases, the PBE0 functional performs better than the B3P86 functional. Regarding the calculated HOFs, all four functionals can yield satisfactory results with deviations of <2 kcal mol-1 from experimental ones for CH2(NO2)2 and CH(NO2)3, when the diffusion functions are not augmented. For the C(NO2)4 molecule, the large basis sets augmented with polarization functions and diffusion functions are required to yield a good result.

Su, Xinfang; Cheng, Xinlu; Liu, Yonggang; Li, Qinghuan

257

Structures and bond energies of the noble gas complexes NgBeO (Ng?Ar, Kr, Xe)  

NASA Astrophysics Data System (ADS)

The geometries, vibrational frequencies and Ng?BeO bond dissociation energies are calculated for the title compounds using quantum chemical methods. The electronic structure of the molecules is investigated with the help of the topological analysis of the electron density distribution. At the MP4 level of theory using effective core potentials for the noble gases and large valence basis sets (quadruple-zeta for Ng, triple-zeta for Be and O, three d and one f type polarization functions), the bond strengths D 0 are predicted after correcting for the BSSE to be 12.6 for XeBeO, 9.3 for KrBeO and 6.7 kcal mol -1 for ArBeO. The Ng?BeO bond of ArBeO and KrBeO is caused by induced dipole interactions, but the Xe?BeO bond has small covalent contributions. The shift of the BeO stretching frequency towards higher wave numbers upon formation of the noble gas complexes is in agreement with the observed blue-shift of the compounds.

Veldkamp, A.; Frenking, G.

1994-08-01

258

Structures and bond energies of the noble gas complexes NgBeO (Ng?Ar, Kr, Xe)  

NASA Astrophysics Data System (ADS)

The geometries, vibrational frequencies and Ng?BeO bond dissociation energies are calculated for the title compounds using quantum chemical methods. The electronic structure of the molecules is investigated with the help of the topological analysis of the electron density distribution. At the MP4 level of theory using effective core potentials for the noble gases and large valence basis sets (quadruple-zeta for Ng, triple-zeta for Be and O, three d and one f type polarization functions), the bond strengths D0 are predicted after correcting for the BSSE to be 12.6 for XeBeO, 9.3 for KrBeO and 6.7 kcal mol -1 for ArBeO. The Ng?BeO bond of ArBeO and KrBeO is caused by induced dipole interactions, but the Xe?BeO bond has small covalent contributions. The shift of the BeO stretching frequency towards higher wave numbers upon formation of the noble gas complexes is in agreement with the observed blue-shift of the compounds.

Veldkamp, A.; Frenking, G.

1994-08-01

259

Metal cation dependence of interactions with amino acids: bond energies of Rb+ to Gly, Ser, Thr, and Pro.  

PubMed

The interactions of rubidium cations with the four amino acids (AA), glycine (Gly), serine (Ser), threonine (Thr), and proline (Pro), are examined in detail. Experimentally, the bond energies are determined using threshold collision-induced dissociation of the Rb(+)(AA) complexes with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy dependent cross sections include consideration of unimolecular decay rates, internal energy of reactant ions, and multiple ion-molecule collisions. 0 K bond energies of 108.9 +/- 7.0, 115.7 +/- 4.9, 122.1 +/- 4.6, and 125.2 +/- 4.5 kJ/mol are determined for complexes of Rb(+) with Gly, Ser, Thr, and Pro, respectively. Quantum chemical calculations are conducted at the B3LYP, B3P86, and MP2(full) levels of theory with geometries and zero point energies calculated at the B3LYP level using both HW*/6-311+G(2d,2p) and Def2TZVP basis sets. Results obtained using the former basis sets are systematically low compared to the experimental bond energies, whereas the latter basis sets show good agreement. For Rb(+)(Gly), the ground state conformer has the rubidium ion binding to the carbonyl group of the carboxylic acid, and a similar geometry is found for Rb(+)(Pro) except the secondary nitrogen accepts the carboxylic acid hydrogen to form the zwitterionic structure. Both Rb(+)(Ser) and Rb(+)(Thr) are found to have tridentate binding at the B3LYP and MP2(full) levels, whereas the B3P86 slightly prefers binding Rb(+) at the carboxylic acid. Comparison of these results to those for the lighter alkali ions provides insight into the trends in binding affinities and structures associated with metal cation variations. PMID:20184306

Bowman, Vanessa N; Heaton, Amy L; Armentrout, P B

2010-03-25

260

Metal cation dependence of interactions with amino acids: bond energies of Cs+ to Gly, Pro, Ser, Thr, and Cys.  

PubMed

The interactions of cesium cations with five amino acids (AA) including glycine (Gly), proline (Pro), serine (Ser), threonine (Thr), and cysteine (Cys) are examined in detail. Experimentally, the bond dissociation energies (BDEs) are determined using threshold collision-induced dissociation of the Cs(+)(AA) complexes with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy-dependent cross sections include consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. Bond dissociation energies (0 K) of 93.3 ± 2.5, 107.9 ± 4.6, 102.3 ± 4.1, 105.4 ± 4.3, and 96.8 ± 4.2 kJ/mol are determined for complexes of Cs(+) with Gly, Pro, Ser, Thr, and Cys, respectively. Quantum chemical calculations are conducted at the B3LYP, B3P86, MP2(full), and M06 levels of theory with geometries and zero-point energies calculated at the B3LYP level using both HW*/6-311+G(2d,2p) and def2-TZVPPD basis sets. Results obtained using the former basis sets are systematically low compared to the experimental bond energies, whereas the latter basis sets show good agreement. For Cs(+)(Gly), theory predicts the ground-state conformer has the cesium cation binding to the carbonyl group of the carboxylic acid. For Cs(+)(Pro), the secondary nitrogen accepts the carboxylic acid hydrogen to form the zwitterionic structure, and the metal cation binds to both oxygens. Cs(+)(Ser), Cs(+)(Thr), and Cs(+)(Cys) are found to have tridentate binding at the MP2(full) level, whereas the density functional approaches slightly prefer bidentate binding of Cs(+) at the carboxylic acid moiety. Comparison of these results to those for the smaller alkali cations provides insight into the trends in binding affinities and structures associated with metal cation variations. PMID:22452793

Armentrout, P B; Chen, Yu; Rodgers, M T

2012-04-26

261

Thermochemical benchmarking of hydrocarbon bond separation reaction energies: Jacob's ladder is not reversed!  

Microsoft Academic Search

We reinvestigate the performance of Kohn–Sham density functional (DF) methods for a thermochemical test set of bond separation reactions of alkanes (BSR36) published recently by Steinmann et al. [J. Chem. Theory Comput. 5, 2950 (2009)]. According to our results, the tested approximations perform for this rather special benchmark as usual. We show that the choice of reference enthalpies plays a

Helge Krieg; Stefan Grimme

2010-01-01

262

Development of chemically bonded ceramic materials for use in thermal-energy-storage devices  

Microsoft Academic Search

The objective of this program is to develop phosphate and calcium aluminate cement bonded ceramic materials based on North Carolina olivine which are capable of serving as the heat storage media in electric furnaces using the off peak power heating concept. These compositions will be castable refractories formed without the conventional step of powder pressing and cured at temperatures below

Brosnan

1982-01-01

263

Aircraft surface coatings study: Energy efficient transport program. [sprayed and adhesive bonded coatings for drag reduction  

NASA Technical Reports Server (NTRS)

Surface coating materials for application on transport type aircraft to reduce drag, were investigated. The investigation included two basic types of materials: spray on coatings and adhesively bonded films. A cost/benefits analysis was performed, and recommendations were made for future work toward the application of this technology.

1979-01-01

264

Communication: The highest frequency hydrogen bond vibration and an experimental value for the dissociation energy of formic acid dimer.  

PubMed

The highest frequency hydrogen bond fundamental of formic acid dimer, ?(24) (B(u)), is experimentally located at 264 cm(-1). FTIR spectra of this in-plane bending mode of (HCOOH)(2) and band centers of its symmetric D isotopologues (isotopomers) recorded in a supersonic slit jet expansion are presented. Comparison to earlier studies at room temperature reveals the large influence of thermal excitation on the band maximum. Together with three B(u) combination states involving hydrogen bond fundamentals and with recent progress for the Raman-active modes, this brings into reach an accurate statistical thermodynamics treatment of the dimerization process up to room temperature. We obtain D(0) = 59.5(5) kJ/mol as the best experimental estimate for the dimer dissociation energy at 0 K. Further improvements have to wait for a more consistent determination of the room temperature equilibrium constant. PMID:22519308

Kollipost, F; Wugt Larsen, R; Domanskaya, A V; Nörenberg, M; Suhm, M A

2012-04-21

265

The Fe-CO bond energy in myoglobin: a QM/MM study of the effect of tertiary structure.  

PubMed

The Fe-CO bond dissociation energy (BDE) in myoglobin (Mb) has been calculated with B3LYP quantum mechanics/molecular mechanics methods for 22 different Mb conformations, generated from molecular dynamics simulations. Our average BDE of 8.1 kcal/mol agrees well with experiment and shows that Mb weakens the Fe-CO bond by 5.8 kcal/mol; the calculations provide detailed atomistic insight into the origin of this effect. BDEs for Mb conformations with the R carbonmonoxy tertiary structure are on average 2.6 kcal/mol larger than those with the T deoxy tertiary structure, suggesting two functionally distinct allosteric states. This allostery is partly explained by the reduction in distal cavity steric crowding as Mb moves from its T to R tertiary structure. PMID:16387767

Strickland, Nikki; Mulholland, Adrian J; Harvey, Jeremy N

2006-02-15

266

Analytic bond-order potentials beyond Tersoff-Brenner. II. Application to the hydrocarbons  

NASA Astrophysics Data System (ADS)

The accuracy of the analytic bond-order potentials (BOP's) that were derived in the previous paper within the tight-binding (TB) formalism is studied for the case of diamond, graphite, and the hydrocarbon molecules. The simplified four-level variant, BOP4S, is found to reproduce the TB bond orders of the C-H and C-C ? bonds to better than 6% due partly to the inclusion of the shape parameter (b2/b1)2. The two-level matrix-derived expression BOP2M is shown to provide a good description of the saturated and conjugate ? bonds, thereby overcoming the deficiencies of the Tersoff potential that are associated with overbinding of radicals and poor treatment of conjugacy. The analytic BOP's reproduce the C-H and C-C bond energies to better than 0.9 eV per bond. The errors would be reduced if the analytic potentials were fitted to experiment rather than predicted directly from known TB parameters.

Oleinik, I. I.; Pettifor, D. G.

1999-04-01

267

Metal-electroceramic bonding in PZT through the selective application of laser energy  

Microsoft Academic Search

Ferrite powder has been directly bonded to the surface of poled lead zirconate titanate (PZT-4) using direct laser sintering.\\u000a The resultant cohesion between the metal and ceramic is extremely good although care must be taken with the processing in\\u000a order to limit the damage inflicted upon the PZT. Four point bending suggests that the strength of the processed samples has

Z. Amin; K. W. Dalgarno; T. P. Comyn; A. W. Tavernor

2006-01-01

268

A Fracture Resisting Molecular Interaction in Trabecular Bone: Sacrificial Bonds and Hidden Length Dissipate Energy as Mineralized Fibrils Separate  

NASA Astrophysics Data System (ADS)

A molecular energy dissipation mechanism in the form of sacrificial bonds and hidden length was previously found in bone constituent molecules of which the efficiency increased with the presence of Ca^2+ ions in the experimental solution. Here we present evidence for how this sacrificial bond-hidden length mechanism contributes to the mechanical properties of the bone composite. From investigations into the nanoscale arrangement of the bone constituents in combination with pico-Newton adhesion force measurements between mineralized collagen fibrils, based on single molecule force spectroscopy, we find evidence that bone consists of mineralized collagen fibrils and a non fibrillar organic matrix which acts as a ``glue'' that holds the mineralized fibrils together. We propose that this ``glue'' resists the separation of mineralized collagen fibrils. Like in the case of the sacrificial bonds in single molecules, the effectiveness of this ``glue'' increases with the presence of Ca^2+ ions. We further investigate how this molecular scale strengthening mechanism increases the fracture toughness of the macroscopic material.

Fantner, Georg E.

2005-03-01

269

Chemical Bonds I  

ERIC Educational Resources Information Center

Chemical bonding is discussed from a bond energy, rather than a wave mechanics, viewpoint. This approach is considered to be more suitable for the average student. (The second part of the article will appear in a later issue of the journal.) (AL)

Sanderson, R. T.

1972-01-01

270

Analysis of hydrogen bond energies and hydrogen bonded networks in water clusters (H2O)20 and (H2O)25 using the charge-transfer and dispersion terms.  

PubMed

The hydrogen bonds and their networks in the water clusters (H2O)20 and (H2O)25 are characterized using the charge-transfer (E(W(a),W(d))(CT)) and dispersion (E(W(a),W(d))(Disp)) terms for every pair of water molecules (Wa, Wd) in the clusters. The terms are evaluated by the perturbation theory based on the ab initio locally projected molecular orbitals (LPMO PT) developed by the present author. The relative binding energies among the isomers evaluated by the LPMO PT agree with those of the high level ab initio wave function based theories. A strong correlation between E(W(a),W(d))(CT) and E(W(a),W(d))(Disp) for the hydrogen bonded pairs is found. The pair-wise interaction energies are characterized by the types of hydrogen-donor (Wd) and hydrogen-acceptor (Wa) water molecules. The strongest pair is that of the D2A1 water molecule as a hydrogen-acceptor and the D1A2 water molecule as a hydrogen-donor, where the DnAm water molecule implies that the water molecule has n hydrogen bonding O-H and m accepting HO. The intra-molecular deformation as well as the O···O distance is also dependent on the types of hydrogen bonded pairs. The ring structures in the cluster are classified by the pattern of alignment of the hydrogen bonds. The lengthening of the hydrogen-bonding OH of Wd is strongly correlated with the charge-transfer (E(W(a),W(d))(CT)) energy. PMID:24800849

Iwata, Suehiro

2014-06-21

271

Effects of density functionals and dispersion interactions on geometries, bond energies and harmonic frequencies of EUX3 (E=N, P, CH; X=H, F, Cl).  

PubMed

Quantum-chemical calculations have been performed to evaluate the geometries, bonding nature and harmonic frequencies of the compounds [EUX3] at DFT, DFT-D3, DFT-D3(BJ) and DFT-dDSc levels using different density functionals BP86, BLYP, PBE, revPBE, PW91, TPSS and M06-L. The stretching frequency of UN bond in [NUF3] calculated with DFT/BLYP closely resembles with the experimental value. The performance of different density functionals for accurate UN vibrational frequencies follows the order BLYP>revPBE>BP86>PW91>TPSS>PBE>M06-L. The BLYP functional gives accurate value of the UE bond distances. The uranium atom in the studied compounds [EUX3] is positively charged. Upon going from [EUF3] to [EUCl3], the partial Hirshfeld charge on uranium atom decreases because of the lower electronegativity of chlorine compared to flourine. The Gopinathan-Jug bond order for UE bonds ranges from 2.90 to 3.29. The UE bond dissociation energies vary with different density functionals as M06-Lbonds in these compound have greater degree of covalent character (in the range 63.8-77.2%). The UE ?-bonding interaction is the dominant bonding interaction in the nitride and methylidyne complexes while it is weaker in [PUX3]. The dispersion energy contributions to the total bond dissociation energies are rather small. Compared to the Grimme's D3(BJ) corrections, the Corminboeuf's dispersion corrections are larger with metaGGA functionals (TPSS, M06-L) while smaller with GGA functionals. PMID:25014545

Pandey, Krishna Kumar; Patidar, Pankaj; Patidar, Sunil Kumar; Vishwakarma, Ravi

2014-12-10

272

Oxaloacetate hydrolase, the C-C bond lyase of oxalate secreting fungi.  

PubMed

Oxalate secretion by fungi is known to be associated with fungal pathogenesis. In addition, oxalate toxicity is a concern for the commercial application of fungi in the food and drug industries. Although oxalate is generated through several different biochemical pathways, oxaloacetate acetylhydrolase (OAH)-catalyzed hydrolytic cleavage of oxaloacetate appears to be an especially important route. Below, we report the cloning of the Botrytis cinerea oahA gene and the demonstration that the disruption of this gene results in the loss of oxalate formation. In addition, through complementation we have shown that the intact B. cinerea oahA gene restores oxalate production in an Aspergillus niger mutant strain, lacking a functional oahA gene. These observations clearly indicate that oxalate production in A. niger and B. cinerea is solely dependent on the hydrolytic cleavage of oxaloacetate catalyzed by OAH. In addition, the B. cinera oahA gene was overexpressed in Escherichia coli and the purified OAH was used to define catalytic efficiency, substrate specificity, and metal ion activation. These results are reported along with the discovery of the mechanism-based, tight binding OAH inhibitor 3,3-difluorooxaloacetate (K(i) = 68 nM). Finally, we propose that cellular uptake of this inhibitor could reduce oxalate production. PMID:17244616

Han, Ying; Joosten, Henk-Jan; Niu, Weiling; Zhao, Zhiming; Mariano, Patrick S; McCalman, Melisa; van Kan, Jan; Schaap, Peter J; Dunaway-Mariano, Debra

2007-03-30

273

In Pursuit of an Ideal C-C Bond-Forming Reaction  

PubMed Central

Attempts to introduce the highly versatile vinyl group into other organic molecules in a chemo-, regio- and stereoselective fashion via catalytic activation of ethylene provided challenging opportunities to explore new ligand and salt effects in homogeneous catalysis. This review provides a personal account of the development of enantioselective reactions involving ethylene.

RajanBabu, T. V.

2009-01-01

274

Thin Bonded P.C.C. Resurfacing: Interim Report Number 1.  

National Technical Information Service (NTIS)

The purpose of this study was to evaluate the construction techniques and performance characteristics of the La. DOTD's first portland cement concrete resurfacing project which was constructed over a short section of an existing 9-inch concrete pavement l...

W. H. Temple M. Rasoulian

1982-01-01

275

Teachers' Domain: Covalent Bonding  

NSDL National Science Digital Library

This Flash interactive tutorial explores covalent bonding, a type of chemical bond that involves sharing of electrons. Learners investigate the attractive and repulsive forces that act on atomic particles and how the sharing of electrons can keep atoms together. See how two hydrogen atoms interact with each other to create a covalent bond. Learn about patterns in the periodic table and how electrostatic potential energy determines the bond length. Teachers' Domain is a growing collection of more than 1,000 free educational resources compiled by researchers and experienced teachers to promote the use of digital resources in the classroom.

2011-08-16

276

Chemical Bonds  

NSDL National Science Digital Library

Electrons are key to forming the two broad categories of chemical bonds: covalent and ionic. Atoms, which have a nucleus surrounded by electrons, are represented in several different ways. In the Chemical Bonds activity, students explore the different kinds of chemical bonds that can form, ranging from non-polar covalent to ionic. In the model depicted above students adjust the electronegativity of two atoms and see the effect it has on electron distribution and bond type.

Consortium, The C.

2011-12-11

277

Detecting malware's failover C&C strategies with squeeze  

Microsoft Academic Search

The ability to remote-control infected PCs is a fundamental component of modern malware campaigns. At the same time, the command and control (C&C) infrastructure that provides this capability is an attractive target for mitigation. In recent years, more or less successful takedown operations have been conducted against botnets employing both client-server and peer-to-peer C&C architectures. To improve their robustness against

Matthias Neugschwandtner; Paolo Milani Comparetti; Christian Platzer

2011-01-01

278

CCSD(T) level interaction energy for halogen bond between pyridine and substituted iodobenzenes: origin and additivity of substituent effects.  

PubMed

The CCSD(T) level interaction energies at the basis set limit (E(int)) were calculated for 33 halogen bonded pyridine complexes with substituted iodobenzenes. The CCSD(T) level electron correlation correction substantially decreases the magnitude of attraction in comparison with the MP2. The E(int) for the pyridine complexes with mono substituted iodobenzenes varies from -3.14 to -4.42 kcal mol(-1), depending on the substituent. The electron-withdrawing substituents such as NO2 enhance the attraction, while the effects of electron-donating substituents reduce. The additivity of the substituent effects is observed for the E(int) of the pyridine complexes with multiple substituted iodobenzenes. The electrostatic interactions are mainly responsible for the substituent effects on the magnitude of the attraction in the halogen-bonded complexes. The electrostatic energy depends significantly on the substituent. They have a strong correlation with the E(int). On the other hand the effects of the substituent on the dispersion energy are small, however the dispersion does contribute greatly to the attraction. PMID:23503841

Tsuzuki, Seiji; Uchimaru, Tadafumi; Wakisaka, Akihiro; Ono, Taizo; Sonoda, Takaaki

2013-04-28

279

Sticker Bonding.  

ERIC Educational Resources Information Center

Introduces a science activity on the bonding of chemical compounds. Assigns students the role of either a cation or anion and asks them to write the ions they may bond with. Assesses students' understanding of charge, bonding, and other concepts. (YDS)

Frazier, Laura Corbin

2000-01-01

280

Gas phase atomic hydrogen induced carbon-carbon bond activation in cyclopropane on the Ni(100) surface  

SciTech Connect

Carbon-carbon activation in adsorbed cyclopropane is observed following exposure to gas phase atomic hydrogen on the Ni(100) surface for temperatures as low as 100 K. Exposure to either gas phase atomic hydrogen or deuterium results in formation of adsorbed propyl. In both cases subsequent reaction between adsorbed propyl and coadsorbed hydrogen/deuterium produces propane at 121 K. The activation of a single C-C bond in adsorbed cyclopropane dominates as indicated by the fact that propane is the only product observed. No multiple C-C bond activation which would result in methane or ethane formation was ever observed. These reactions and their mechanisms have been investigated using temperature-programmed reaction and vibrational spectroscopy using high-resolution electron energy loss spectroscopy. The results obtained clearly indicate that C-C bond activation occurs during exposure to gas phase atomic hydrogen. Isotopic labeling studies reveal that the adsorbed propyl intermediate is hydrogenated by labelled surface hydrogen. Carbon-carbon bond activation in adsorbed cyclopropane has never been observed during adsorption on a surface with preadsorbed hydrogen nor during exposure to nascent hydrogen formed by dissociating molecular hydrogen. A detailed potential energy diagram for the reactions of adsorbed cyclopropane on the Ni(100) surface is developed based on results from these experiments and the literature. 68 refs., 11 figs., 1 tab.

Son, K.A.; Gland, J.L. [Univ. of Michigan, Ann Arbor, MI (United States)] [Univ. of Michigan, Ann Arbor, MI (United States)

1996-10-30

281

Characterization of Brazed Joints of C-C Composite to Cu-clad-Molybdenum  

NASA Technical Reports Server (NTRS)

Carbon-carbon composites with either pitch+CVI matrix or resin-derived matrix were joined to copper-clad molybdenum using two active braze alloys, Cusil-ABA (1.75% Ti) and Ticusil (4.5% Ti). The brazed joints revealed good interfacial bonding, preferential precipitation of Ti at the composite/braze interface, and a tendency toward de-lamination in resin-derived C-C composite due to its low inter-laminar shear strength. Extensive braze penetration of the inter-fiber channels in the pitch+CVI C-C composites was observed. The relatively low brazing temperatures (<950 C) precluded melting of the clad layer and restricted the redistribution of alloying elements but led to metallurgically sound composite joints. The Knoop microhardness (HK) distribution across the joint interfaces revealed sharp gradients at the Cu-clad-Mo/braze interface and higher hardness in Ticusil (approx.85-250 HK) than in Cusil-ABA (approx.50-150 HK). These C-C/Cu-clad-Mo joints with relatively low thermal resistance may be promising for thermal management applications.

Singh, M.; Asthana, R.

2008-01-01

282

On the Construction of Diabatic and Adiabatic Potential Energy Surfaces Based on Ab Initio Valence Bond Theory‡  

PubMed Central

A theoretical model is presented for deriving effective diabatic states based on ab initio self-consistent field valence bond (VBSCF) theory by reducing the multi-configurational VB Hamiltonian into an effective two-state model. We describe two computational approaches for the optimization of the effective diabatic configurations, resulting in two ways of interpreting such effective diabatic states. In the variational diabatic configuration (VDC) method, the energies of the individual diabatic states are variationally minimized. In the consistent diabatic configuration (CDC) method, both the configuration coefficients and orbital coefficients are simultaneously optimized to minimize the adiabatic ground-state energy in VBSCF calculations. In addition, we describe a mixed molecular orbital and valence bond (MOVB) approach to construct the CDC diabatic and adiabatic states for a chemical reaction, whereas the VDC-MOVB method has been described previously. Employing the symmetric SN2 reaction between NH3 and CH3NH3+ as a test system, we found that the results from ab initio VBSCF and from MOVB calculations are in good agreement, suggesting that the computationally efficient MOVB method is a reasonable model for VB simulations of condensed phase reactions. The results indicate that CDC and VDC diabatic states converge, respectively, to covalent and ionic states as the molecular geometries are distorted from the minimum of the respective diabatic state along the reaction coordinate. Furthermore, the resonance energy that stabilizes the energy of crossing between the two diabatic states, resulting in the transition state of the adiabatic ground-state reaction, has a strong dependence on the overlap integral between the two diabatic states and is a function of both the exchange integral and the total diabatic ground-state energy.

Song, Lingchun; Gao, Jiali

2009-01-01

283

The strong aromatic hydrogen bonding in crystalline propargylammonium tetraphenylborate  

NASA Astrophysics Data System (ADS)

Crystalline propargylammonium tetraphenylborate contains strong N +?H and moderate C?C?H hydrogen bond donors, but no conventional acceptors. Therefore, the donors can only form ?-type hydrogen bonds with the phenyl groups of the anion, leading to a dense system of aromatic hydrogen bonds which involves also the ethynyl groups. For the latter, this is the first documented case of C?C?H·Ph hydrogen bonds in an ionic compound; the infrared absorption spectrum shows very similar characteristics as previously observed for C?C?H·Ph interactions in uncharged systems. The distances of the donor H-atoms to the aromatic centroids are in the range 2.08-2.37 Å for N +?H and 2.55-2.77 Å for C?C?H donors.

Steiner, Thomas; Schreurs, Antoine M. M.; Kanters, Jan A.; Kroon, Jan; van der Maas, John; Lutz, Bert

1997-12-01

284

Reactions of Co sup + , Ni sup + , and Cu sup + with cyclopropane and ethylene oxide. Metal-methylidene ion bond energies  

SciTech Connect

The reactions of atomic cobalt, nickel, and copper ions with cyclopropane and ethylene oxide have been studied by using guided ion beam mass spectrometry. A predominant process in all these systems is formation of MCH{sub 2}{sup +}. Analyses of these endothermic reactions yield the bond energies D{sup 0} (Co{sup +}-CH{sub 2}) = 77.5 {plus minus} 2.3 kcal/mol, D{sup 0}(Ni{sup +}-CH{sub 2}) = 75.2 {plus minus} 1.8 kcal/mol, and D{sup 0}(Cu{sup +}-CH{sub 2}) = 63.9 {plus minus} 1.6 kcal/mol. Differences between these values and those derived from earlier studies for Co{sup +} and Ni{sup +} are discussed. In addition to D{sup 0} (M{sup +}-CH{sub 2}), bond energies for Co{sup +}-H, M-H, (M = Co, Ni, Cu) and M{sup +}-O and M-O (M = Co, Ni) are evaluated and lower limits are placed on D{sup 0} (M{sup +}-C{sub 2}H{sub 4}) and D{sup 0} (M{sup +}-C{sub 2}H{sub 2}) (M = Co, Ni, Cu). The reaction mechanism for these reactions is also discussed in detail.

Fisher, E.R.; Armentrout, P.B. (Univ. of Utah, Salt Lake City (USA))

1990-02-22

285

Describing the chemical bonding in C70 and C70O3 – A quantum chemical topology study  

NASA Astrophysics Data System (ADS)

Cc–Cc and Ca–Cb bonds in C70 have dominant characteristics of double bonds, whereas the remaining six other types of bonds are single bonds with contributions from ?-electron density. 'Single' bonds can act as active sites in chemical reactions which would typically require a multiple bond, such as addition of an ozone molecule, due to the fact that all adjacent bonds can serve as an efficient source of ?-electron density. Thus any alteration in the electron density distribution following functionalization has far-reaching impact. We note that formation of the most stable ozonide isomer causes the smallest total perturbation in the electron density of the parent fullerene and C–C bond evolution correlates well with the shape of the minimum energy path for the ozone ring opening reaction on the fullerene surface. Finally, we observe that the O–O bond in C70O3 is protocovalent, and as such resembles the O–O bond in H2O2.

Bil, Andrzej; Latajka, Zdzis?aw; Hutter, Jürg; Morrison, Carole A.

2014-03-01

286

CC bond formation at polynuclear metal centers  

Microsoft Academic Search

Studies on C-C bond formation between simple hydrocarbon species such as CH2, C=CH2, CH=CH2, CH2=CH2, CH2=C=CH2 and CH=CH at a diruthenium center suggest that the process is promoted when the dimetal center can readily compensate for the two electrons “lost” in the formation of the new C-C bond. Thus, whereas µ-CH2 and ethene combine only under forcing conditions, the combination

Selby A. R. Knox

1992-01-01

287

Bond Dissociation Energies of the Tungsten Fluorides and Their Singly-Charged Ions: A Density Functional Survey  

NASA Technical Reports Server (NTRS)

The dissociation of WF6 and the related singly-charged cations and anions into the lower fluorides and fluorine atoms has been investigated theoretically using density functional theory (B3LYP) and relativistic effective core potentials, with estimates of spin-orbit effects included using a simple model. The inclusion of spin-orbit is essential for a correct description of the thermochemistry. The total atomization energy of the neutral and anionic WF6 is reproduced to within 25 kcal/mol, but comparison of individual bond dissociation energies with available experimental data shows discrepancies of up to 10 kcal/mol. The results are nevertheless useful to help resolve discrepancies in experimental data and provide estimates of missing data.

Dyall, Kenneth G.; Arnold, James (Technical Monitor)

1999-01-01

288

A DFT study of cyclopropane adsorption on Pt(1 1 1). Electronic structure and bonding  

NASA Astrophysics Data System (ADS)

We have studied the adsorption of cyclopropane (c-C3H6) on Pt(1 1 1) by means of the density functional theory (DFT). We have investigated the preferential adsorption geometry, considering different adsorption sites and bonding configurations for the molecular adsorbate. We have also computed the electronic structure and bonding interactions by means of density of states (DOS), crystal orbital overlap population (OPDOS), and overlap population (OP) analysis. Our results show a small preference for Bridge and Top adsorption sites with the cyclopropane ring parallel to the surface. Ptsbnd C equilibrium distance is ?3.5 Å and a weak bond is formed during adsorption. The main bonding interaction comes from the Ptsbnd H overlap population. Pt 5pz orbitals play an important role in the bonding between c-C3H6 and the surface. We have found that Van der Waals (vdW) corrections to the energies improve the adsorption values without changing the preferential site geometries.

Germán, E.; López-Corral, I.; Pirillo, S.; Juan, A.; Brizuela, G.

2014-06-01

289

Amino Acid Mean Excitation Energies and Directional Dependencies from Core and Bond Calculations  

SciTech Connect

We determine the mean excitation energies of several amino acids using a Bragg Rule developed for molecular fragments or functional groups. As the composition of the amino acids is very similar, we find that the amino acids have similar mean excitation energies (approximately 70 eV). Differences arise from variation of the side chains (-R); addition of-CH2-groups decreases the mean excitation energy. We also speculate concerning the directional dependence of the amino acid mean excitation energies.

Sabin, John R.; Oddershede, Jens [Department of Physics, University of Florida, Gainesville, FL 32611 (United States); Institute for Physics and Chemistry, University of Southern Denmark, Campusvej 55, DK-5230 Odense M (Denmark); Sauer, Stephan P. A. [Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen (Denmark)

2008-12-08

290

Modelling ab initio non-bonded interactions for sigma bond, pi bond, and lone pair orbitals  

NASA Astrophysics Data System (ADS)

Ab initio eigenvalue splittings between symmetric and anti-symmetric combinations of energetically degenerate and environmentally equivalent molecular orbitals (MOs) are presented for pairs of ethane molecules and pairs of formaldehyde molecules in various geometrical configurations and as a function of separation. These weak non-bonded orbital interactions are computed for the MO of C?C sigma bond character in ethane, and for MOs of C?O pi bond character and those of axial and perpendicular oxygen lone pair character in formaldehyde. The relationship between simple orbital overlaps and the Hartree—Fock splittings in this beyond-van-der-Waals distance range is examined using overlaps based on valence bond wavefunctions constructed from single zeta Slater type orbitals. The role of the hydrogen atoms interposed in the region between the interacting MOs is examined. The suitability of the computed interactions as calibrations of effective transfer integrals needed in macromolecular electronic analyses is discussed.

Gruschus, James M.; Kuki, Atsuo

1992-05-01

291

Unexpected interplay of bonding height and energy level alignment at heteromolecular hybrid interfaces  

NASA Astrophysics Data System (ADS)

Although geometric and electronic properties of any physical or chemical system are always mutually coupled by the rules of quantum mechanics, counterintuitive coincidences between the two are sometimes observed. The coadsorption of the organic molecules 3,4,9,10-perylene tetracarboxylic dianhydride and copper-II-phthalocyanine on Ag(111) represents such a case, since geometric and electronic structures appear to be decoupled: one molecule moves away from the substrate while its electronic structure indicates a stronger chemical interaction, and vice versa for the other. Our comprehensive experimental and ab-initio theoretical study reveals that, mediated by the metal surface, both species mutually amplify their charge-donating and -accepting characters, respectively. This resolves the apparent paradox, and demonstrates with exceptional clarity how geometric and electronic bonding parameters are intertwined at metal–organic interfaces.

Stadtmüller, Benjamin; Lüftner, Daniel; Willenbockel, Martin; Reinisch, Eva M.; Sueyoshi, Tomoki; Koller, Georg; Soubatch, Serguei; Ramsey, Michael G.; Puschnig, Peter; Tautz, F. Stefan; Kumpf, Christian

2014-04-01

292

On the Enthalpy of Formation of Hydroxyl Radical and Gas-Phase Bond Dissociation Energies of Water and Hydroxyl  

SciTech Connect

Several photoionization experiments utilizing the positive ion cycle to derive the O-H bond energy converge to a consensus value of AE0(OH+/H2O)= 146117? 24 cm-1 (18.1162? 0.0030 eV). With the most accurate currently available ZEKE value. IE(OH)= 104989? 2 cm-1, corroborated by a number of photoelectron measurements,Error! Bookmark not defined.,Error! Bookmark not defined.,Error! Bookmark not defined.,Error! Bookmark not defined. this leads to D0(H?OH)= 41128? 24 cm-1= 117.59? 0.07 kcal/mol. This corresponds to DHf 0(OH)= 8.85? 0.07 kcal/mol, and implies D0(OH)= 35593? 24 cm-1= 101.76? 0.07 kcal/mol. The most sophisticated theoretical calculations performed so far on the HxO system, CCSD(T)/aug-cc-pVnZ, n=Q, 5, 6, and 7, extrapolated to the CBS limit and including corrections for core-valence effects, scalar relativistic effects, incomplete correlation recovery, and diagonal Born-Oppenheimer corrections reproduce the experimental results to within 0.0 - 0.2 k cal/mol. The new values of the two successive bond dissociation energies of water supersede the previously accepted values,Error! Bookmark not defined.,Error! Bookmark not defined. which were based on spectroscopic determinationsError! Bookmark not defined.,Error! Bookmark not defined. of D0(OH) using a very short Birge-Sponer extrapolation on OH/OD A1S+. An exhaustive analysis of the latter approach, combined with the application of the same procedure on a calculated potential energy curve for the state in question, demonstrates that the Birge-Sponer extrapolation underestimates the bond dissociation energy, in spite of the fact that only the last vibrational level was not observed experimentally. The new values affect a large number of other thermochemical quantities which directly or indirectly rely on or refer to D0(H-OH), D0(OH), or DHf?(OH).

Ruscic, Branko (Argonne National Laboratory); Wagner, Albert F. (Argonne Naitonal Laboratory); Harding, Lawerence B. (Argonne National Laboratory); Asher, Robert L. (Argonne National Laboratory); Feller, David F. (BATTELLE (PACIFIC NW LAB)); Dixon, David A. (BATTELLE (PACIFIC NW LAB)); Peterson, Kirk A. (WASHINGTON STATE UNIV TC); Song, Yang (Ames Laboratory); Qian, Ximei (Ames Laboratory); Ng, C Y. (Iowa State University); Liu, Jianbo (Lawrence Berkeley National Laboratory); Wenwu, Chen (Lawrence Berkeley National Laboratory)

2001-12-01

293

High-Resolution Photoelectron Spectroscopic Study of Cyclopropene (c-C_3H_4)  

NASA Astrophysics Data System (ADS)

The spectroscopic information available on the cyclopropene radical cation is limited to that contained in low-resolution He I photoelectron spectra. To better characterize the structure of this cation, we have recently measured high-resolution PFI-ZEKE photoelectron spectra of c-C_3H_4 and several of its deuterated isotopomers in the vicinity of the adiabatic ionization threshold. Our new data include fully rotationally resolved spectra of the origin band of the widetilde{X}^+?widetilde{X} transition of c-C_3H_4 and spectra of the low-vibrational levels of c-C_3H_4 and the deuterated isotopomers recorded at lower resolution. Because our efforts at synthesizing the partially deuterated isotopomers always resulted in mixtures of several isotopomers, differing in their number of D atoms and in the location of these atoms, the analysis of the isotopic shifts turned out to be challenging. Combining the information contained in the rotational structure of the origin band of c-C_3H_4 with the ionization energies of the isotopomers measured by photoionization mass spectrometry and the vibrational structure observed in the PFI-ZEKE spectra of the mixtures of deuterated isotopomers, we were able to draw conclusions on the structure of the cyclopropene radical cation based solely on experimental data. The adiabatic ionization energy of c-C_3H_4 was determined to be 77931.8(5) {cm}-1. M. B. Robin, C. R. Brundle, N. A. Kuebler, G. B. Ellison and K. B. Wiberg, J. Chem. Phys. 57, 1758 (1972). P. Bischof and E. Heilbronner, Helv. Chim. Acta 53, 1677 (1970).

Vasilatou, Konstantina; Michaud, Julie M.; Grassi, Guido; Baykusheva, Denitsa; Merkt, Frederic

2012-06-01

294

Technology of bonding elastomers  

NASA Astrophysics Data System (ADS)

The paper reviews current bonding theories and examines the application of these concepts to the production of reliable commercial bonding elastomers. Fundamental aspects of elastomer bonding (such as the elastomer surface thermodynamics, the mechanics of the adhesive failure, and the elastomer self-adhesion) are discussed along with the types of elastomers and the technology used in producing these compounds, with particular consideration given to the factors affecting the strength and durability of elastomer bonds. Tables are presented listing elastomers' designations according to ASTM D1418; the elastomers' surface properties; the elastomer surface energy dispersive and polar components; the commonly used elastomer types selected to meet specific ASTM test requirements; the ASTM adhesion test methods; and selected metal primers, cover coats, and bonding agents.

Symes, Ted; Oldfield, David

295

Ultrasonically bonded value assembly  

NASA Technical Reports Server (NTRS)

A valve apparatus capable of maintaining a fluid-tight seal over a relatively long period of time by releasably bonding a valve member to its seat is described. The valve member is bonded or welded to the seat and then released by the application of the same energy to the bond joint. The valve member is held in place during the bonding by a clamping device. An appropriate force device can activate the opening and closing of the valve member. Various combinations of material for the valve member and valve seat can be utilized to provide an adequate sealing bond. Aluminum oxide, stainless steel, inconel, tungsten carbide as hard materials and copper, aluminum, titanium, silver, and gold as soft materials are suggested.

Salvinski, R. J. (inventor)

1975-01-01

296

Free Energy Landscapes for S-H Bonds in (Cp2Mo2S4)-Mo-star Complexes  

SciTech Connect

Extensive thermochemical data have been determined for a series of complexes derived from Cp*Mo(? S)2(? SMe)(? SH)MoCp* and Cp*Mo(? S)2(? SH)2MoCp*. These data include electrochemical potentials, pKa values, homolytic solution bond dissociation free energies (SBDFEs), and hydride donor abilities in acetonitrile. Thermochemical data ranged from +0.6 to -2.0 V vs FeCp2+/o for electrochemical potentials, 5 to 31 for pKa values, 43 to 68 kcal/mol for homolytic SBDFEs, and 44 to 84 kcal/mol for hydride donor abilities. The observed values for these thermodynamic parameters are comparable to those of many transition metal hydrides, which is consistent with the many parallels in the chemistry of these two classes of compounds. The wealth of thermochemical data are presented in free energy landscapes as a useful approach to visualizing and understanding the relative stabilities of all of the species under specified conditions. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.

Appel, Aaron M.; Lee, Suh-Jane; Franz, James A.; DuBois, Daniel L.; Rakowski DuBois, Mary

2009-03-23

297

Electronic structure and energies of interatomic bonds in the TiSi2 compound with a C49 crystal structure  

NASA Astrophysics Data System (ADS)

Full-electron calculations of the electronic structure of the TiSi2 compound in the structural modification C49 are performed using the augmented-plane-wave method. The total energy, the electronic band structure, and the density of states are calculated for an extended translational unit cell Ti4Si8, which is formed during the growth of a silicon nanowire on a p-Si substrate. Calculations are also carried out for two orthorhombic unit cells of the nonstoichiometric compositions Ti3Si9 and Ti5Si7. The energies of the interatomic bonds are determined to be E Si-Si = 1.8 eV, E Ti-Ti = 2.29 eV, and E Ti-Si = 4.47 eV. The dependence of the total energy of the unit cell E tot(V) on the unit cell volume V is obtained by optimizing the unit cell volume. The bulk modulus B 0 = 132 GPa is determined from the Murnaghan equation of state for solids and the dependence E tot (V). This value of the bulk modulus is used to estimate the activation energy for interstitial diffusion of silicon atoms Q i(Si) ? 0.8 eV.

Shanina, B. D.; Grigor'ev, N. N.; Klimovskaya, A. I.; Kamins, T. I.

2007-01-01

298

Guided ion beam studies of the reactions of Co n+ (n=1-18) with N2: Cobalt cluster mononitride and dinitride bond energies.  

PubMed

The reactions of Co n+ (n=1-18) with N2 are measured as a function of kinetic energy over a range of 0-15 eV in a guided ion beam tandem mass spectrometer. A variety of Co m +, Co m N+, and Co m N2+ (mBond dissociation energies for both cobalt cluster nitrides and dinitrides are derived from threshold analysis of the energy dependence of the endothermic reactions using several different approaches. These values show only a mild dependence on cluster size over the range studied, although the Co13+-N bond energy is relatively weak. The bond energies of Co n+-N for larger clusters suggest that a reasonable value for the desorption energy of atomic nitrogen from bulk phase cobalt is 6.3+/-0.2 eV, which is somewhat lower than the only available value in the literature, an estimate based on the enthalpy of formation of bulk cobalt nitride. The trends in the cobalt nitride thermochemistry are also compared to previously determined metal-metal bond energies, D 0(Co n+-Co), and to D 0(Fe n+ -N). Implications for catalytic ammonia production using cobalt versus iron are discussed. PMID:18500871

Liu, Fuyi; Li, Ming; Tan, Lin; Armentrout, P B

2008-05-21

299

Collision-induced dissociation of Fe sub n sup + ( n =2--19) with Xe: Bond energies, geometric structures, and dissociation pathways  

SciTech Connect

The kinetic energy dependence of the collision-induced dissociation (CID) of Fe{sup +}{sub {ital n}} ({ital n}=11--19) with Xe is studied by using a guided ion beam mass spectrometer. As previously reported for smaller iron cluster ions, these iron cluster ions dissociate exclusively by evaporation, the sequential loss of Fe atoms. Bond energies for the larger iron cluster ions {ital D}{sup 0}(Fe{sup +}{sub {ital n}{minus}1}--Fe), {ital n}=11--19, as well as updated values for the smaller cluster ions, {ital n}=2--10, are reported. These energies are derived after explicit consideration of the effect of secondary collisions between Fe{sup +}{sub {ital n}} and Xe, and of the lifetimes of the energized iron cluster ions. Bond energies for neutral iron clusters are derived by combining these ionic bond energies with literature ionization energies for Fe{sub {ital n}}. Except for the dimers, we find that the bond energies of ionic and neutral iron clusters are very similar and change nonmonotonically as a function of cluster size, with local maxima at {ital n}=6, 7, 13, 15, and 19; and local minima at {ital n}=8, 14, and 18. Evidence for the existence of weakly bound isomers of iron cluster ions is also observed.

Lian, L.; Su, C.; Armentrout, P.B. (Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States))

1992-09-15

300

Collision-induced dissociation of Ni sup + sub n ( n =2--18) with Xe: Bond energies, geometrical structures, and dissociation pathways  

SciTech Connect

The kinetic energy dependence of the collision-induced dissociation (CID) of Ni{sup +}{sub {ital n}} ({ital n}=2--18) with xenon is studied by using a guided ion beam mass spectrometer. Bond energies of nickel cluster ions, {ital D}{sup 0}(Ni{sup +}{sub {ital n}{minus}1}--Ni), are determined from measurements of the CID thresholds. Bond energies for neutral nickel clusters, {ital D}{sup 0}(Ni{sub {ital n}{minus}1}--Ni), are derived by combining these ionic bond energies with literature values of ionization energies for Ni{sub {ital n}}. Both {ital D}{sup 0}(Ni{sup +}{sub {ital n}{minus}1}--Ni) and {ital D}{sup 0}(Ni{sub {ital n}{minus}1}--Ni) are found to increase nonmonotonically as a function of cluster size, with local maxima at {ital n}=3, 7, and 13 for ionic clusters and at {ital n}=6 and 13 for neutral clusters. Examination of the cluster size dependence of nickel cluster bond energies leads to speculations on the likely cluster geometric structures. Examination of the general dissociation behavior over a broad collision energy range shows that nickel cluster ions dissociate primarily by sequential atom loss, although exceptions are noted.

Lian, L.; Su, C.; Armentrout, P.B. (Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States))

1992-05-15

301

Pressure-driven variations of hydrogen bonding energy in ammonium azide (NH4N3): IR absorption and Raman scattering studies.  

PubMed

In this study, high pressure infrared (IR) absorption and Raman scattering studies for ammonium azide (NH4N3) were carried out at room temperature up to 20 GPa and 22 GPa, respectively. For comparison and further assignment, the vibrational spectra at ambient conditions were calculated using CASTEP code, particularly for the far- and mid-IR modes. The recorded vibrational data consistently indicated a pressure-induced phase transition at 2.9 GPa. All observed vibrational modes maintained their identities at the high pressure phase, indicating that NH4N3 was still presented in the form of ammonium cations and azide anions linked by the hydrogen bond (N-H?N). Above 2.9 GPa, the relative magnitude of the torsional mode weakened and the N-H symmetric stretch displayed a redshift, indicating strengthened hydrogen bonding energy. The opposite effects were observed above 12 GPa, where the relative magnitude of the torsional mode strengthened and the N-H symmetric stretch reverted to a blueshift, indicating weakened hydrogen bonding energy. It can be concluded that the hydrogen bonding energy exhibited a weakening (0-2.9 GPa), strengthening (2.9-12 GPa), and then again weakening (12-22 GPa) phenomena with the increasing of compression. The hydrogen bonding energy changing with the increase of pressure can be ascribed to a phase transition at 2.9 GPa and a rotational or bending behavior of azide ions at 12 GPa. PMID:25028034

Wu, Xiaoxin; Ma, Fengxian; Ma, Chunli; Cui, Hang; Liu, Zhenxian; Zhu, Hongyang; Wang, Xiaoli; Cui, Qiliang

2014-07-14

302

Hydrogen bonding effects on the reorganization energy for photoinduced charge separation reaction between porphyrin and quinone studied by nanosecond laser flash photolysis.  

PubMed

Alcohol concentration dependences of photoinduced charge separation (CS) reaction of zinc tetraphenyl-porphyrin (ZnTPP) and duroquinone (DQ) were investigated in benzonitrile by a nanosecond laser flash photolysis technique. The photoinduced CS reaction was accelerated by the addition of alcohols, whereas the addition of acetonitrile caused little effect on the CS reactions. The simple theory was developed to calculate an increase in reorganization energies induced by the hydrogen bonding interactions between DQ and alcohols using the chemical equilibrium constants for the hydrogen bonding complexes through the concerted pathway and the stepwise one. The experimental results were analyzed by using the Marcus equation where we took into account the hydrogen bonding effects on the reorganization energy and the reaction free energy for the CS reaction. The observed alcohol concentration dependence of the CS reaction rates was well explained by the formation of the hydrogen bonding complexes through the concerted pathway, demonstrating the increase in the reorganization energy by the hydrogen bonding interactions. PMID:20121118

Yago, Tomoaki; Gohdo, Masao; Wakasa, Masanobu

2010-02-25

303

Combining preprocessor slicing with C\\/C++ language slicing  

Microsoft Academic Search

Of the very few practical implementations of program slicing algorithms, the majority deal with C\\/C++ programs. Yet, preprocessor-related issues have been marginally addressed by these slicers, despite the fact that ignoring (or only partially handling) these constructs may lead to serious inaccuracies in the slicing results and hence in the program analysis task being performed. Recently, an accurate slicing method

László Vidács; Árpád Beszédes; Tibor Gyimóthy

2009-01-01

304

Thermodynamic properties of carbon in b.c.c. and f.c.c. iron-silicon-carbon solid solutions.  

NASA Technical Reports Server (NTRS)

The equilibrium between hydrogen-methane gas mixtures and Fe-Si-C solid solutions has been investigated both as a function of temperature and carburizing gas composition. The thermodynamic properties of the carbon atoms in both b.c.c. and f.c.c. solid solution have been derived from the equilibrium measurements. The results found have been compared with those of earlier investigations and with the predictions of recent theoretical models on ternary solid solutions containing both substitutional and interstitial solute atoms.

Chraska, P.; Mclellan, R. B.

1971-01-01

305

Multilayer oxidation protective coating for C\\/C composites from room temperature to 1500 °C  

Microsoft Academic Search

To prevent carbon\\/carbon (C\\/C) composites from oxidation, a multilayer oxidation resistant coating was prepared. The inner SiC coating was prepared by pack cementation, and the outer SiC–MoSi2 three-layer coating was obtained by slurry coating using silicon–sol as the caking agent. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to analyze the phase, microstructure and element distribution

Fu Qian-Gang; Li He-Jun; Wang Yong-Jie; Li Ke-Zhi; Tao Jun

2010-01-01

306

Structures, energies, bonding, and NMR properties of pnicogen complexes H2XP:NXH2 (X ? H, CH3, NH2, OH, F, Cl).  

PubMed

Ab initio calculations have been carried out in a systematic investigation of P···N pnicogen complexes H(2)XP:NXH(2) for X ? H, CH(3), NH(2), OH, F, and Cl, as well as selected complexes with different substituents X bonded to P and N. Binding energies for complexes H(2)XP:NXH(2) range from 8 to 27 kJ mol(-1) and increase to 39 kJ mol(-1) for H(2)FP:N(CH(3))H(2). Equilibrium structures have a nearly linear A-P-N arrangement, with A being the atom directly bonded to P. Binding energies correlate with intermolecular N-P distances as well as with bonding parameters obtained from AIM and SAPT analyses. Complexation increases (31)P chemical shieldings in complexes with binding energies greater than 19 kJ mol(-1). One-bond spin-spin coupling constants (1p)J(N-P) across the pnicogen interaction exhibit a quadratic dependence on the N-P distance for complexes H(2)XP:NXH(2), similar to the dependence of (2h)J(X-Y) on the X-Y distance for complexes with X-H···Y hydrogen bonds. However, when the mixed complexes H(2)XP:NX'H(2) are included, the curvature of the trendline changes and the good correlation between (1p)J(N-P) and the N-P distance is lost. PMID:22047040

Del Bene, Janet E; Alkorta, Ibon; Sanchez-Sanz, Goar; Elguero, José

2011-11-24

307

C.C.D. Readout of a Picosecond Streak Camera with an Intensified C.C.D.  

National Technical Information Service (NTIS)

This paper deals with a digital streak camera readout device. The device consists in a low light level television camera made of a solid state C.C.D. array coupled to an image intensifier associated to a video-digitizer coupled to a micro-computer system....

M. Lemonier J. C. Richard C. Cavailler A. Mens G. Raze

1984-01-01

308

Forming Bonds.  

ERIC Educational Resources Information Center

Explains how one North Carolina school district was able to pass high-dollar bond issues for school construction. Discusses the planning and bidding processes, and the district's philosophy towards incorporating innovative changes in design and equipment. (GR)

Spoor, Dana L.

1998-01-01

309

The strain energy release rates in adhesively bonded balanced and unbalanced specimens and lap joints  

Microsoft Academic Search

An analytical model is developed to determine the strain energy release rate in adhesive joints of various configurations such as the double-cantilever beam and single-lap joints. The model is based on asymptotic analysis of adhesive layer stresses and Irwin’s crack closure integral. Closed-form solutions are presented for balanced and unbalanced joints under mode I, II and mixed-mode I\\/II that take

Khaled Shahin; Farid Taheri

2008-01-01

310

A Promising Tool to Achieve Chemical Accuracy for Density Functional Theory Calculations on Y-NO Homolysis Bond Dissociation Energies  

PubMed Central

A DFT-SOFM-RBFNN method is proposed to improve the accuracy of DFT calculations on Y-NO (Y = C, N, O, S) homolysis bond dissociation energies (BDE) by combining density functional theory (DFT) and artificial intelligence/machine learning methods, which consist of self-organizing feature mapping neural networks (SOFMNN) and radial basis function neural networks (RBFNN). A descriptor refinement step including SOFMNN clustering analysis and correlation analysis is implemented. The SOFMNN clustering analysis is applied to classify descriptors, and the representative descriptors in the groups are selected as neural network inputs according to their closeness to the experimental values through correlation analysis. Redundant descriptors and intuitively biased choices of descriptors can be avoided by this newly introduced step. Using RBFNN calculation with the selected descriptors, chemical accuracy (?1 kcal·mol?1) is achieved for all 92 calculated organic Y-NO homolysis BDE calculated by DFT-B3LYP, and the mean absolute deviations (MADs) of the B3LYP/6-31G(d) and B3LYP/STO-3G methods are reduced from 4.45 and 10.53 kcal·mol?1 to 0.15 and 0.18 kcal·mol?1, respectively. The improved results for the minimal basis set STO-3G reach the same accuracy as those of 6-31G(d), and thus B3LYP calculation with the minimal basis set is recommended to be used for minimizing the computational cost and to expand the applications to large molecular systems. Further extrapolation tests are performed with six molecules (two containing Si-NO bonds and two containing fluorine), and the accuracy of the tests was within 1 kcal·mol?1. This study shows that DFT-SOFM-RBFNN is an efficient and highly accurate method for Y-NO homolysis BDE. The method may be used as a tool to design new NO carrier molecules.

Li, Hong Zhi; Hu, Li Hong; Tao, Wei; Gao, Ting; Li, Hui; Lu, Ying Hua; Su, Zhong Min

2012-01-01

311

A quinone-assisted photoformation of energy-rich chemical bonds  

NASA Technical Reports Server (NTRS)

In a study of biochemical means of solar energy conversion, ADP and inorganic phosphates were converted to ATP by white light in the nonaqueous solvent dimethylformamide in the presence of tetrachloro-p-quinone or ubiquinone. Conversion of ADP to ATP has been accomplished in aqueous suspension by the use of cell-like structures aggregated from poly(aspartic acid, glutamic acid, tyrosine). This is believed to occur through the formation of dopaquinone in the peptide structure during illumination. The way in which the quantitative yield of ATP has been influenced by pH and by added substances, such as FeCl2, was studied.

Fox, S. W.; Adachi, T.; Stillwell, W.

1980-01-01

312

Probing the bonding in nitrogen-doped graphene using electron energy loss spectroscopy.  

PubMed

Precise control of graphene properties is an essential step toward the realization of future graphene devices. Defects, such as individual nitrogen atoms, can strongly influence the electronic structure of graphene. Therefore, state-of-the-art characterization techniques, in conjunction with modern modeling tools, are necessary to identify these defects and fully understand the synthesized material. We have directly visualized individual substitutional nitrogen dopant atoms in graphene using scanning transmission electron microscopy and conducted complementary electron energy loss spectroscopy experiments and modeling which demonstrates the influence of the nitrogen atom on the carbon K-edge. PMID:23869545

Nicholls, Rebecca J; Murdock, Adrian T; Tsang, Joshua; Britton, Jude; Pennycook, Timothy J; Koós, Antal; Nellist, Peter D; Grobert, Nicole; Yates, Jonathan R

2013-08-27

313

Comparative studies of MCMB and C?C composite as anodes for lithium-ion battery systems  

NASA Astrophysics Data System (ADS)

Mesocarbon microbead (MCMB 2528) and C?C composite have been investigated as anodes for lithium-ion batteries using half-cells with lithium counter electrode and three electrode cell systems containing LiCoO 2 cathode and lithium reference electrodes in 1 M LiPF 6 electrolyte (EC/DMC 1:1 v/v). The test results show that the practical capacity of C?C composite anode is 50% higher than that of MCMB-based anode (based on total anode weight). The irreversible capacity loss of C?C composite is significantly lower than that of MCMB carbon. Lithium-ion cells made with C?C composite anode can accept repeated overdischarge without performance deterioration. The extra capacity of C?C composite can be utilized to improve energy density and safety issues related to overcharge of lithium-ion cells. Differential scanning calorimetry (DSC) results indicates that the thermal stability of fully charged C?C composite anode (lithiated anode) is much better than that of fully charged MCMB anode.

Hossain, Sohrab; Kim, Yong-Kyu; Saleh, Yousry; Loutfy, Raouf

314

Strength of Chemical Bonds  

NASA Technical Reports Server (NTRS)

Students are not generally made aware of the extraordinary magnitude of the strengths of chemical bonds in terms of the forces required to pull them apart. Molecular bonds are usually considered in terms of the energies required to break them, and we are not astonished at the values encountered. For example, the Cl2 bond energy, 57.00 kcal/mole, amounts to only 9.46 x 10(sup -20) cal/molecule, a very small amount of energy, indeed, and impossible to measure directly. However, the forces involved in realizing the energy when breaking the bond operate over a very small distance, only 2.94 A, and, thus, f(sub ave) approx. equals De/(r - r(sub e)) must be very large. The forces involved in dissociating the molecule are discussed in the following. In consideration of average forces, the molecule shall be assumed arbitrarily to be dissociated when the atoms are far enough separated so that the potential, relative to that of the infinitely separated atoms, is reduced by 99.5% from the potential of the molecule at the equilibrium bond length (r(sub e)) for Cl2 of 1.988 A this occurs at 4.928 A.

Christian, Jerry D.

1973-01-01

315

Energy localization in HMX-Estane polymer-bonded explosives during impact loading  

NASA Astrophysics Data System (ADS)

We report the results of a mechanistic study of energy localization in aHMX (High Melting point eXplosive octahydro-1,3,5,7-tetranitro-1,2,3,5-tetrazocine)/Estane PBX system during dynamic loading. The focus is on the thermal-mechanical response over the strain rate range of 104 - 105 s-1 under different confinement conditions. A recently developed cohesive finite element method is used to track and analyze the contributions to heating from different constituents, interfaces, deformation and fracture mechanisms, and internal friction. In particular, energy dissipations due to viscoelastic deformation, grain fracture, interfacial debonding, and friction along crack faces are quantified as functions of time and overall deformation. The materials analyzed have HMX volume fractions between 0.69 and 0.82. Calculations show that variation in strain rate can significantly affect the spatial distribution but not the overall number of hot spots. Higher confining stresses lead to more intense heating in the binder and more uniform distribution of hot spots. The evolution of hot spots is quantified as a function of loading condition, deformation and microstructural attributes. The microstructure-response relations obtained can be used to assess the initiation sensitivity of energetic composites.

Barua, A.; Horie, Y.; Zhou, M.

2012-03-01

316

Establishment of heterolytic and homolytic Y-NO2 bond dissociation energy scales of nitro-containing compounds in acetonitrile: chemical origin of NO2 release and capture.  

PubMed

The first heterolytic and homolytic N(O)-NO(2) bond dissociation energy scales of three types Y-nitro (Y = N, O) compounds and corresponding radical anions in acetonitrile were established by using titration calorimetry combined with relevant electrochemical data through proper thermodynamic cycles. PMID:18307353

Li, Xin; Zhu, Xiao-Qing; Zhang, Fan; Wang, Xiao-Xiao; Cheng, Jin-Pei

2008-03-21

317

Photodissociation measurements of bond dissociation energies: Ti[sup +][sub 2], V[sup +][sub 2], Co[sup +][sub 2], and Co[sup +][sub 3  

SciTech Connect

The bond dissociation energies of Ti[sup +][sub 2], V[sup +][sub 2], Co[sup +][sub 2], and Co[sup +][sub 3] have been measured from the sudden onset of predissociation in the photodissociation spectra of these molecules, yielding values of [ital D][sup [circ

Russon, L.M.; Heidecke, S.A.; Birke, M.K.; Conceicao, J.; Morse, M.D.; Armentrout, P.B. (Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States))

1994-04-01

318

Sequential bond energies of Fe+ (CO2)n, n = 1-5, determined by threshold collision-induced dissociation and ab initio theory.  

PubMed

Collision-induced dissociation of the Fe+ (CO2)n complexes for n = 1-5 is studied using kinetic energy dependent guided ion beam mass spectrometry. In all cases, the primary products are endothermic loss of an intact neutral ligand from the complex. The cross section thresholds are interpreted to yield 0 K bond energies after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and unimolecular decay rates. These values are compared with density functional theoretical values for all five complexes. Theory provides bond energies in reasonable agreement with experiment for n = 1-4 and predictions for the infrared spectroscopy of these complexes that agree nicely with experimental results of Gregoire and Duncan (J. Chem. Phys. 2002, 117, 2120). Our thermochemical results are also compared with the Fe+ (CO)n and Fe+ (N2)n complexes, previously studied. PMID:16354023

Armentrout, P B; Koizumi, Hideya; MacKenna, Meghan

2005-12-22

319

Adaptive pressure ultrasonic precise bonding method for polymer micro joint  

Microsoft Academic Search

Ultrasonic precise bonding for polymer micro joint was studied. Considering shape deviation as the key issue to successful micro bonding, an ultrasonic bonding system was established, which employed 60 kHz ultrasonic transducer that achieved bonding at low amplitude. Adaptive ultrasonic bonding with bonding energy auto-selected was proposed. In this method, continues decreasing pressure was imposed on the micro components, the

Yibo Sun; Yi Luo; Yuqi Feng; Xiaodong Wang

2010-01-01

320

Chemical Distribution and Bonding of Lithium in Intercalated Graphite: Identification with Optimized Electron Energy Loss Spectroscopy  

SciTech Connect

Direct mapping of the lithium spatial distribution and the chemical state provides critical information on structure-correlated lithium transport in electrode materials for lithium batteries. Nevertheless, probing lithium, the lightest solid element in the periodic table, poses an extreme challenge with traditional X-ray or electron scattering techniques due to its weak scattering power and vulnerability to radiation damage. Here, we report nanoscale maps of the lithium spatial distribution in electrochemically lithiated graphite using electron energy loss spectroscopy in the transmission electron microscope under optimized experimental conditions. The electronic structure of the discharged graphite was obtained from the near-edge fine structure of the Li and C K-edges and ab initio calculations. A 2.7 eV chemical shift of the Li K-edge, along with changes in the density of states, reveals the ionic nature of the intercalated lithium with significant charge transfer to the graphene sheets. Direct mapping of lithium in graphite revealed nanoscale inhomogeneities (nonstoichiometric regions), which are correlated with local phase separation and structural disorder (i.e., lattice distortion and dislocations) as observed by high-resolution transmission electron microscopy. The surface solid-electrolyte interphase (SEI) layer was also imaged and determined to have a thickness of 10-50 nm, covering both edge and basal planes with LiF as its primary inorganic component. The Li K-edge spectroscopy and mapping, combined with electron microscopy-based structural analysis provide a comprehensive view of the structure-correlated lithium intercalation in graphite and of the formation of the SEI layer.

Zhu, Y.; Wang, F.; Graetz, J.; Moreno, M.S.; Ma, C.; Wu, L.; Volkov, V.

2011-02-01

321

Ground States of Conjugated Molecules. Xv. Bond Localization and Resonance Energies in Compounds Containing Nitrogen or Oxygen.  

National Technical Information Service (NTIS)

The heats of formation of, and bond lengths in a number of classical conjugated molecules containing nitrogen or oxygen have been calculated by the method previously developed by the authors. The results imply that the bonds in compounds of this type can ...

M. J. S. Dewar A. J. Harget N. Trinajstic

1969-01-01

322

Transport properties for a mixture of the ablation products C, C2, and C3  

NASA Technical Reports Server (NTRS)

The ablation of carbon-phenolic heat shields upon entry into the atmosphere of one of the outer planets leads to the injection of large amounts of C, C2, and C3 into the shock layer. These species must be included in the calculation of transport properties in the shock layer. The kinetic theory of gases has been used to obtain accurate results for the transport properties of monatomic carbon. The Hulburt-Hirschelder potential, the most accurate general purpose atom-atom potential for states with an attractive minimum, was used to represent such states and repulsive states were represented by fitting quantum mechanical potential energy curves with the exponential repulsive potential. These results were orientation averaged according to the peripheral force model to obtain transport collision integrals for the C-C2 and C2-C2 interaction. Results for C3 were obtained by ignoring the presence of the central carbon atom. The thermal conductivity, viscosity, and diffusion coefficients for pure C, C2, and C3, and for mixtures of these gases, were then calculated from 1000 K - 25,000 K.

Biolsi, L.; Fenton, J.; Owenson, B.

1981-01-01

323

Block-Localized Density Functional Theory (BLDFT), Diabatic Coupling, and Their Use in Valence Bond Theory for Representing Reactive Potential Energy Surfaces  

PubMed Central

A multistate density functional theory in the framework of the valence bond model is described. The method is based on a block-localized density functional theory (BLDFT) for the construction of valence-bond-like diabatic electronic states and is suitable for the study of electron transfer reactions and for the representation of reactive potential energy surfaces. The method is equivalent to a valence bond theory with the treatment of the localized configurations by using density functional theory (VBDFT). In VBDFT, the electron densities and energies of the valence bond states are determined by BLDFT. A functional estimate of the off-diagonal matrix elements of the VB Hamiltonian is proposed, making use of the overlap integral between Kohn–Sham determinants and the exchange-correlation functional for the ground state substituted with the transition (exchange) density. In addition, we describe an approximate approach, in which the off-diagonal matrix element is computed by wave function theory using block-localized Kohn–Sham orbitals. The key feature is that the electron density of the adiabatic ground state is not directly computed nor used to obtain the ground-state energy; the energy is determined by diagonalization of the multistate valence bond Hamiltonian. This represents a departure from the standard single-determinant Kohn–Sham density functional theory. The multistate VBDFT method is illustrated by the bond dissociation of H2+ and a set of three nucleophilic substitution reactions in the DBH24 database. In the dissociation of H2+, the VBDFT method yields the correct asymptotic behavior as the two protons stretch to infinity, whereas approximate functionals fail badly. For the SN2 nucleophilic substitution reactions, the hybrid functional B3LYP severely underestimates the barrier heights, while the approximate two-state VBDFT method overcomes the self-interaction error, and overestimates the barrier heights. Inclusion of the ionic state in a three-state model, VBDFT(3), significantly improves the computed barrier heights, which are found to be in accord with accurate results. The BLDFT method is a versatile theory that can be used to analyze conventional DFT results to gain insight into chemical bonding properties, and it is illustrated by examining the intricate energy contributions to the ion–dipole complex stabilization.

Cembran, Alessandro; Song, Lingchun; Mo, Yirong; Gao, Jiali

2010-01-01

324

Determination of N-NO bond dissociation energies of N-methyl-N-nitrosobenzenesulfonamides in acetonitrile and application in the mechanism analyses on NO transfer.  

PubMed

The heterolytic and homolytic N-NO bond dissociation energies of seven substituted N-methyl-N-nitrosobenzenesulfonamides (abbreviated as G-MNBS, G = p-OCH(3), p-CH(3), p-H, p-Cl, p-Br, 2,5-2Cl, m-NO(2)) in acetonitrile solution were evaluated for the first time by using titration calorimetry and relative thermodynamic cycles according to Hess' law. The results show that the energetic scales of the heterolytic and homolytic N-NO bond dissociation energies of G-MNBS in acetonitrile solution cover the ranges from 44.3 to 49.5 and from 33.0 to 34.9 kcal/mol for the neutral G-MNBS, respectively, which indicates that N-methyl-N-nitrosobenzenesulfonamides are much easier to release a NO radical (NO(*)) than to release a NO cation (NO(+)). The estimation of the heterolytic and homolytic (N-NO)(-)(*) bond dissociation energies of the seven G-MNBS radical anions in acetonitrile solution gives the energetic ranges of -15.8 to -12.9 and -3.1 to 1.8 kcal/mol for the (N-NO)(-)(*) bond homolysis and heterolysis, respectively, which means that G-MNBS radical anions are very unstable at room temperature and able to spontaneously or easily release a NO radical or NO anion (NO(-)), but releasing a NO radical is easier than releasing NO anion. These determined N-NO bond dissociation energies of G-MNBS and their radical anions have been successfully used in the mechanism analyses of NO transfer from G-MNBS to 3,6-dibromocarbazole and the reactions of NO with the substituted N-methyl-benzenesulfonamide nitranions (G-MBSN(-)) in acetonitrile solution. PMID:15725027

Zhu, Xiao-Qing; Hao, Wei-Fang; Tang, Hui; Wang, Chun-Hua; Cheng, Jin-Pei

2005-03-01

325

Spectroscopic identification of bond strain and pi interactions in a series of saturated carbon-cage molecules: adamantane, twistane, octahedrane, and cubane  

NASA Astrophysics Data System (ADS)

Novel nanocarbons such as fullerenes, nanotubes, graphene, and nanodiamond reside at the cutting edge of nanoscience and technology. Along with chemical functionalization, geometrical constraints such as extreme curvature or defects in crystallites can modify the electronic properties. This paper presents a fundamental study of how bond strain affects electronic structure in a benchmark series of novel saturated carbon cage compounds. Adamantane, the smallest diamondoid, has carbon atoms commensurate with the diamond lattice. Twistane has the same stoichiometry (C10H16), but introduces some bond strain into the cage. Octahedrane (C12H12) and cubane (C8H8) have increasing strain, culminating in cubane where C-C bonds lie either parallel, or orthogonal to one another. Using gas-phase NEXAFS spectroscopy, we observe the broad C-C ?* splits into two more narrow and intense resonances with increasing strain. Also, LUMO states associated with tertiary C-H ?* broaden and shift to lower energy, and are 3X more intense in cubane than octadedrane. The differences are entirely due to the shape rather than stoichiometry, and indicate, we believe, some ? interaction between parallel C-C bonds in the cubane.

Willey, Trevor M.; Lee, J. R. I.; van Buuren, T.; Landt, L.; Schreiner, P. R.; Fokin, A. A.; Tkachenko, B. A.; Fokina, N. A.; Brehmer, D.

2011-03-01

326

A Simple Test to Determine the Effectiveness of Different Braze Compositions for Joining Ti-Tubes to C/C Composite Plates  

NASA Technical Reports Server (NTRS)

A simple tube-plate joint tensile test was implemented to compare the effectiveness of commercial brazes, namely, TiCuNi, TiCuSil, and Cu-ABA, used for bonding Ti-tubes joined to C-C composite plates. The different braze systems yielded different; yet, repeatable results. The Cu-ABA system proved to have about twice the load-carrying ability of the other two systems due to the fact that the bonded area between the braze material and the C-C plate was largest for this system. The orientation of the surface fiber tows also had a significant effect on load-carrying ability with tows oriented perpendicular to the tube axis displaying the highest failure loads. Increasing the process load and modifying the surface of the C-C plate by grooving out channels for the Ti-Tube to nest in resulted in increased load-carrying ability for the TiCuSil and Cu-ABA systems due to increased bonded area and better penetration of the braze material into the C-C composite.

Morscher, Gregory N.; Singh, Mrityunjay; Shpargel, Tarah; Asthana, Rajiv

2006-01-01

327

Metal cation dependence of interactions with amino acids: bond energies of Rb+ and Cs+ to Met, Phe, Tyr, and Trp.  

PubMed

The interactions of rubidium and cesium cations with four amino acids (AA) including methionine (Met), phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp) are examined in detail. Experimentally, the bond dissociation energies (BDEs) are determined using threshold collision-induced dissociation of the Rb(+)(AA) and Cs(+)(AA) complexes with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy dependent cross sections include consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. 0 K BDEs of 121.0 ± 7.0 (102.8 ± 6.6), 123.8 ± 7.2 (112.9 ± 5.5), 125.8 ± 7.4 (115.6 ± 6.9), and 138.1 ± 7.5 (125.0 ± 6.8) kJ/mol are determined for complexes of Rb(+) (Cs(+)) with Met, Phe, Tyr, and Trp, respectively. Quantum chemical calculations are conducted at the B3LYP, MP2(full), and M06 levels of theory with geometries and zero point energies calculated at the B3LYP level using def2-TZVPPD basis sets. Results obtained using all three levels show good agreement with experiment, with B3LYP values being systematically low and MP2(full) and M06 values being systematically high. At 0 and 298 K, theory predicts the ground-state conformers for M(+)(Met) either have tridentate binding of the metal cation to the carbonyl, amino, and sulfur groups (MP2 and M06) or to both oxygens of a zwitterionic conformation (B3LYP). At 298 K, binding to the carboxylic acid group and the sulfur also becomes competitive. For the aromatic amino acids at 0 K, most levels of theory favor tridentate binding of the metal ions to the backbone carbonyl and amino groups along with the ?-cloud of the ring, whereas for Rb(+)(Trp) and Cs(+)(AA), B3LYP theory favors binding to only the carbonyl and ring groups. At 298 K, B3LYP favors the latter binding mode for all three Rb(+)(aromatic AA) complexes. Comparison of these results to those for the smaller alkali cations provides insight into the trends in binding affinities and structures associated with metal cation variations. PMID:23514190

Armentrout, P B; Yang, Bo; Rodgers, M T

2013-04-11

328

A reduced radial potential energy function for the halogen bond and the hydrogen bond in complexes B···XY and B···HX, where X and Y are halogen atoms.  

PubMed

It is shown by considering 76 halogen- and hydrogen-bonded complexes BXY and BHX (where B is a Lewis base N2, CO, C2H2, C2H4, H2S, HCN, H2O, PH3 or NH3 and X, Y are F, Cl, Br or I) that the intermolecular stretching force constants k? (determined from experimental centrifugal distortion constants via a simple model) and the intermolecular dissociation energies D? (calculated at the CCSD(T)(F12*)/cc-pVDZ-F12 level of theory) are related by D? = C?k?, where C? = 1.50(3) × 10(3) m(2) mol(-1). This suggests that one-dimensional functions implying direct proportionality of D? and k?, (e.g. a Morse or Rydberg function) might serve as reduced radial potential energy functions for such complexes. PMID:24827860

Legon, Anthony C

2014-06-28

329

Molecular beam pulsed-discharge Fourier transform microwave spectra of CH 3-C?C-F, CH 3-(C?C) 2-F, and CH 3-(C?C) 3-F  

NASA Astrophysics Data System (ADS)

The methylfluoroacetylenes CH 3-(C?C) 2-F and CH 3-(C?C) 3-F have been generated for the first time in a pulsed-discharge nozzle and characterized by molecular beam Fourier transform microwave spectroscopy in the 5-26 GHz frequency range. The spectroscopic constants B=1086.44824(13) MHz, DJ=0.02044(70) kHz, and DJK=7.083(91) kHz of CH 3-(C?C) 2-F and B=478.908444(34) MHz, DJ=0.003060(98) kHz, and DJK=1.899(22) kHz of CH 3-(C?C) 3-F have been determined. In addition, the 13C isotopic species of CH 3-C?C-F in their natural abundances have been measured, and a partial substitution structure of CH 3-C?C-F has been derived and compared with those of related fluorine derivatives.

Blanco, Susana; Sanz, M. Eugenia; Mata, Santiago; Lesarri, Alberto; López, Juan C.; Dreizler, Helmut; Alonso, José L.

2003-07-01

330

Photochemical tissue bonding  

DOEpatents

Photochemical tissue bonding methods include the application of a photosensitizer to a tissue and/or tissue graft, followed by irradiation with electromagnetic energy to produce a tissue seal. The methods are useful for tissue adhesion, such as in wound closure, tissue grafting, skin grafting, musculoskeletal tissue repair, ligament or tendon repair and corneal repair.

Redmond, Robert W. (Brookline, MA); Kochevar, Irene E. (Charlestown, MA)

2012-01-10

331

A mild route to mesoporous Mo2C-C hybrid nanospheres for high performance lithium-ion batteries.  

PubMed

In this work, we have developed a mild route to fabricate typically mesoporous Mo2C-C hybrid nanospheres based on a solvothermal synthesis and reduction-carbonization process. This work opens a low-temperature route to synthesize valuable carbides. The resultant Mo2C-C hybrid, for the first time, is used as an anode material in lithium ion batteries (LIBs). Compared with bulk Mo2C, the Mo2C-C hybrid exhibits much better electrochemical performance. Remarkably, the hybrid electrode can deliver a specific capacity of over 670 mA h g(-1) after 50 cycles at 100 mA g(-1), which is much higher than that of the bulk material (113 mA h g(-1)). Even cycled at a high current density of 1000 mA g(-1), high capacities of around 400-470 mA h g(-1) can still be retained for the Mo2C-C hybrid. It might benefit from the synergistic effect of the nanohybridization, effectively relieving the volume change during the repeated lithium insertion-extraction reactions and maintaining the integrity of the electrical connections. It is expected that the present synthesis strategy for the Mo2C-C hybrid can be extended to other nanostructured carbides with good energy storage performance. PMID:24791274

Gao, Qing; Zhao, Xinyu; Xiao, Ying; Zhao, Di; Cao, Minhua

2014-06-01

332

Microwave bonding of MEMS component  

NASA Technical Reports Server (NTRS)

Bonding of MEMs materials is carried out using microwave. High microwave absorbing films are placed within a microwave cavity, and excited to cause selective heating in the skin of the material. This causes heating in one place more than another. Thereby minimizing the effects of the bonding microwave energy.

Barmatz, Martin B. (Inventor); Mai, John D. (Inventor); Jackson, Henry W. (Inventor); Budraa, Nasser K. (Inventor); Pike, William T. (Inventor)

2005-01-01

333

Coulombic Models in Chemical Bonding.  

ERIC Educational Resources Information Center

Describes a bonding theory which provides a framework for the description of a wide range of substances and provides quantitative information of remarkable accuracy with far less computational effort than that required of other approaches. Includes applications, such as calculation of bond energies of two binary hydrides (methane and diborane).…

Sacks, Lawrence J.

1986-01-01

334

25 CFR 225.30 - Bonds.  

Code of Federal Regulations, 2013 CFR

...30 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS OIL AND GAS, GEOTHERMAL, AND SOLID MINERALS AGREEMENTS Minerals Agreements § 225.30 Bonds. (a) Bonds required by provisions of a...

2014-04-01

335

Clarifying Chemical Bonding. Overcoming Our Misconceptions.  

ERIC Educational Resources Information Center

Demonstrations to help students change their misconceptions about chemical bond breaking are presented. Students' misconceptions about chemical bonds in both biological and chemical systems are discussed. A calculation for the release of energy from respiration is presented. (KR)

Hapkiewicz, Annis

1991-01-01

336

Defect structures in deformed F.C.C. metals  

SciTech Connect

A high density of small defect clusters, similar to those observed in irradiated or quenched metals, has been observed in the deformed f.c.c. metals Cu, Au and Ni. The preliminary results show that the defect clusters are predominantly stacking fault tetrahedral (SFT). The SFT number density, rather than the size distribution, is deformation dependent. The defect cluster density is greater in the vicinities of dislocation tangles and grain boundaries. Their size distribution is wider than that produced by irradiation with an important number of larger clusters being formed. It is argued that these deformation-produced clusters may play a role in determining the flow stress and work hardening at low deformations.

Dai, Y.; Victoria, M. [Ecole Polytechnique Federale de Lausanne, Villigen PSI (Switzerland). CRPP-Fusion Technology Div.] [Ecole Polytechnique Federale de Lausanne, Villigen PSI (Switzerland). CRPP-Fusion Technology Div.

1997-08-01

337

Improving the Accuracy of Density Functional Theory (DFT) Calculation for Homolysis Bond Dissociation Energies of Y-NO Bond: Generalized Regression Neural Network Based on Grey Relational Analysis and Principal Component Analysis  

PubMed Central

We propose a generalized regression neural network (GRNN) approach based on grey relational analysis (GRA) and principal component analysis (PCA) (GP-GRNN) to improve the accuracy of density functional theory (DFT) calculation for homolysis bond dissociation energies (BDE) of Y-NO bond. As a demonstration, this combined quantum chemistry calculation with the GP-GRNN approach has been applied to evaluate the homolysis BDE of 92 Y-NO organic molecules. The results show that the ull-descriptor GRNN without GRA and PCA (F-GRNN) and with GRA (G-GRNN) approaches reduce the root-mean-square (RMS) of the calculated homolysis BDE of 92 organic molecules from 5.31 to 0.49 and 0.39 kcal mol?1 for the B3LYP/6-31G (d) calculation. Then the newly developed GP-GRNN approach further reduces the RMS to 0.31 kcal mol?1. Thus, the GP-GRNN correction on top of B3LYP/6-31G (d) can improve the accuracy of calculating the homolysis BDE in quantum chemistry and can predict homolysis BDE which cannot be obtained experimentally.

Li, Hong Zhi; Tao, Wei; Gao, Ting; Li, Hui; Lu, Ying Hua; Su, Zhong Min

2011-01-01

338

Dispersion-correcting potentials can significantly improve the bond dissociation enthalpies and noncovalent binding energies predicted by density-functional theory  

NASA Astrophysics Data System (ADS)

Dispersion-correcting potentials (DCPs) are atom-centered Gaussian functions that are applied in a manner that is similar to effective core potentials. Previous work on DCPs has focussed on their use as a simple means of improving the ability of conventional density-functional theory methods to predict the binding energies of noncovalently bonded molecular dimers. We show in this work that DCPs developed for use with the LC-?PBE functional along with 6-31+G(2d,2p) basis sets are capable of simultaneously improving predicted noncovalent binding energies of van der Waals dimer complexes and covalent bond dissociation enthalpies in molecules. Specifically, the DCPs developed herein for the C, H, N, and O atoms provide binding energies for a set of 66 noncovalently bonded molecular dimers (the "S66" set) with a mean absolute error (MAE) of 0.21 kcal/mol, which represents an improvement of more than a factor of 10 over unadorned LC-?PBE/6-31+G(2d,2p) and almost a factor of two improvement over LC-?PBE/6-31+G(2d,2p) used in conjunction with the "D3" pairwise dispersion energy corrections. In addition, the DCPs reduce the MAE of calculated X-H and X-Y (X,Y = C, H, N, O) bond dissociation enthalpies for a set of 40 species from 3.2 kcal/mol obtained with unadorned LC-?PBE/6-31+G(2d,2p) to 1.6 kcal/mol. Our findings demonstrate that broad improvements to the performance of DFT methods may be achievable through the use of DCPs.

DiLabio, Gino A.; Koleini, Mohammad

2014-05-01

339

Two important factors influencing shock sensitivity of nitro compounds: Bond dissociation energy of X–NO 2 (X = C, N, O) and Mulliken charges of nitro group  

Microsoft Academic Search

DFT\\/BLYP\\/DNP is employed to calculate bond dissociation energy of X–NO2 (X=C, N, O) and Mulliken charges of nitro group of 14 kinds of nitro compounds, and partial least squares approximation is applied to linearly fit their shock initiation pressure (p90%,TMD). It is found that the fitted values are in good agreement with the experimental shock initiation pressures. The fitted model

Bisheng Tan; Xinping Long; Rufang Peng; Hongbo Li; Bo Jin; Shijin Chu; Haishan Dong

2010-01-01

340

Strength of the bond between a silicone lining material and denture resin after Er:YAG laser treatments with different pulse durations and levels of energy  

Microsoft Academic Search

The purpose of this study was to investigate the tensile strength of the bond between a silicone lining material and heat-cured\\u000a polymethyl methacrylate (PMMA) denture base resin after Er:YAG laser treatment with different pulse durations and energy levels.\\u000a PMMA test specimens were fabricated and each received one of six surface treatments: no treatment (control), and five Er:YAG\\u000a laser treatments comprising

Faik Tugut; Hakan Akin; Burcu Mutaf; Gulsah Emine Akin; Ali Kemal Ozdemir

341

Design and Evaluation of a 2D Array PIN Photodiode Bump Bonded to Readout IC for the Low Energy X-ray Detector  

Microsoft Academic Search

A 2D array radiation sensor, consisting of an array of PIN photodiodes bump bonded to readout integrated circuit (IC), has been developed for operation with low energy X-rays. The PIN photodiode array and readout IC for this system have been fabricated. The main performance measurements are the following: a few pA-scale leakage current, 350 pF junction capacitance, 30 mum-depth depletion

Sunwoo Yuk; Shin-Woong Park; Yun Yi

2006-01-01

342

Dispersion-correcting potentials can significantly improve the bond dissociation enthalpies and noncovalent binding energies predicted by density-functional theory.  

PubMed

Dispersion-correcting potentials (DCPs) are atom-centered Gaussian functions that are applied in a manner that is similar to effective core potentials. Previous work on DCPs has focussed on their use as a simple means of improving the ability of conventional density-functional theory methods to predict the binding energies of noncovalently bonded molecular dimers. We show in this work that DCPs developed for use with the LC-?PBE functional along with 6-31+G(2d,2p) basis sets are capable of simultaneously improving predicted noncovalent binding energies of van der Waals dimer complexes and covalent bond dissociation enthalpies in molecules. Specifically, the DCPs developed herein for the C, H, N, and O atoms provide binding energies for a set of 66 noncovalently bonded molecular dimers (the "S66" set) with a mean absolute error (MAE) of 0.21 kcal/mol, which represents an improvement of more than a factor of 10 over unadorned LC-?PBE/6-31+G(2d,2p) and almost a factor of two improvement over LC-?PBE/6-31+G(2d,2p) used in conjunction with the "D3" pairwise dispersion energy corrections. In addition, the DCPs reduce the MAE of calculated X-H and X-Y (X,Y = C, H, N, O) bond dissociation enthalpies for a set of 40 species from 3.2 kcal/mol obtained with unadorned LC-?PBE/6-31+G(2d,2p) to 1.6 kcal/mol. Our findings demonstrate that broad improvements to the performance of DFT methods may be achievable through the use of DCPs. PMID:24832350

DiLabio, Gino A; Koleini, Mohammad

2014-05-14

343

Preparation and characterization of SiC\\/C and C\\/SiC\\/C composites using pulse chemical vapor infiltration process  

Microsoft Academic Search

A porous carbon plate and carbon fiber\\/carbon composite (C\\/C) preforms were infiltrated with SiC using a pulse chemical vapor infiltration (Pulse-CVI) process, and the Pulse-CVI conditions for obtaining the densely infiltrated SiC\\/C or C\\/SiC\\/C composites were examined. The optimum reaction temperatures, at which the pores were uniformly filled with SiC deposits throughout the thickness, were 1173 K for the carbon

Akihito Sakai; Jun Gotoh; Seiji Motojima

1996-01-01

344

Theoretical study of bond distances and dissociation energies of actinide oxides AnO and AnO2.  

PubMed

In the present study we evaluated trends in the bond distances and dissociation enthalpies of actinide oxides AnO and AnO(2) (An = Th-Lr) on the basis of consistent computed data obtained by using density functional theory in conjunction with relativistic small-core pseudopotentials. Computations were carried out on AnO (An = Th-Lr) and AnO(2) (An = Np, Pu, Bk-Lr) species, while for the remaining AnO(2) species recent literature data (Theor. Chem. Acc. 2011, 129, 657) were utilized. The most important computed properties include the geometries, vibrational frequencies, dissociation enthalpies, and several excited electronic states. These molecular properties of the late actinide oxides (An = Bk-No) are reported here for the first time. We present detailed analyses of the bond distances, covalent bonding properties, and dissociation enthalpies. PMID:22471700

Kovács, Attila; Pogány, Peter; Konings, Rudy J M

2012-04-16

345

Pi Bond Orders and Bond Lengths  

ERIC Educational Resources Information Center

Discusses three methods of correlating bond orders and bond lengths in unsaturated hydrocarbons: the Pauling theory, the Huckel molecular orbital technique, and self-consistent-field techniques. (MLH)

Herndon, William C.; Parkanyi, Cyril

1976-01-01

346

Guided ion beam studies of the reactions of Crn+ (n=2-14) with D 2: cluster-deuteride bond energies as a chemical probe of cluster electronic structure  

NASA Astrophysics Data System (ADS)

The kinetic energy dependencies of the reactions of chromium cluster cations, Crn+ (n=2-14) , with D 2 are studied in a guided ion beam mass spectrometer. The observed products are CrnD+ (n=2-14) and CrnD2+ (n=6-14) . All reactions are observed to exhibit thresholds, except for formation of the dideuteride product for Crn+ (n=6-8) . Threshold analyses of the endothermic reactions reveal binding energies for the first deuterium atom to the cluster ions as a function of cluster size. The Cr n+-D bond energies are compared to previously determined metal-metal bond energies, D0(Cr n+-Cr). The bond energies of Cr n+-D exhibit odd-even oscillations with n that parallel those of Cr n+-Cr. These trends support our earlier suggestion that bonding in Cr n+ clusters, at least for n=2-11, are governed by electronic factors.

Conceição, J.; Liyanage, R.; Armentrout, P. B.

2000-12-01

347

Guided ion beam studies of the reactions of V{sub n}{sup +} (n=2{endash}17) with O{sub 2}: Bond energies and dissociation pathways  

SciTech Connect

The kinetic energy dependence of the reactions of V{sub n}{sup +} (n=2{endash}17) with oxygen is studied using a guided ion beam mass spectrometer. In all but the smallest clusters, the primary reaction process at low energies is the formation of a vanadium cluster dioxide ion which then loses one or two vanadium atoms or a vanadium oxide diatom (VO). Vanadium atom loss is the preferred reaction pathway for large clusters (n{ge}5), whereas loss of VO is more favorable for the smallest reactant clusters (n{le}4). As the collision energy is increased, these primary products dissociate further by loss of additional vanadium atoms. Bond dissociation energies of the vanadium cluster oxides are determined by analysis of the kinetic energy dependence of several different products. The effect of oxygen atoms on the stabilities of vanadium cluster ions is discussed and compared with bulk phase thermochemistry. {copyright} {ital 1998 American Institute of Physics.}

Xu, J.; Rodgers, M.T.; Griffin, J.B.; Armentrout, P.B. [Department of Chemistry, University of Utah, Salt Lake City, Utah84112 (United States)] [Department of Chemistry, University of Utah, Salt Lake City, Utah84112 (United States)

1998-06-01

348

Bond energy of IrO+: guided ion-beam and theoretical studies of the reaction of Ir+ (5F) with O2.  

PubMed

The kinetic-energy dependence of the Ir(+) + O2 reaction is examined using guided ion-beam mass spectrometry. The cross section for IrO(+) formation from ground state Ir(+)((5)F) is unusual, and several means are used to interpret the kinetic energy dependence for IrO(+) formation. In analogy with recent observations for the analogous Re(+) and Os(+) systems, we believe the cross section is most accurately analyzed assuming there are two features. This analysis yields a threshold leading to D0(Ir(+)-O) = 4.26 ± 0.09 eV, with the higher energy feature having a threshold 0.72 ± 0.25 eV higher in energy. This bond energy, which is consistent with much less precise values determined in the literature, can be combined with literature information to suggest that D0(IrO) = 4.25 ± 0.44 eV and IE(IrO) = 8.96 ± 0.45 eV. The nature of the bonding for IrO(+) and IrO2(+) is discussed and analyzed primarily using theoretical calculations at the B3LYP/def2-TZVPPD level of theory. Bond energies for ground state IrO(+), identified as (5)?, are calculated at this level as well as BP86 and CCSD(T,full) levels using several different basis sets. BP86 theoretical bond energies are higher than the experimental value, whereas B3LYP and CCSD(T,full) values are slightly lower, especially after estimated spin-orbit corrections. Potential energy surfaces for the reaction of Ir(+) with O2 are also calculated at the B3LYP/def2-TZVPPD level of theory and reveal that ground state Ir(+)((5)F) inserts into O2 by forming several different Ir(+)(O2) complexes. These can then couple along additional surfaces to form low-lying states of the dioxide IrO2(+). The very interesting parallel behavior of the Re, Os, and Ir heavy metal systems is explored in terms of adiabatic and nonadiabatic behavior, although no unambiguous explanation is evident. PMID:23898975

Armentrout, P B; Li, Feng-Xia

2013-08-22

349

The bond energy of ReO+: guided ion-beam and theoretical studies of the reaction of Re+ (7S) with O2.  

PubMed

The kinetic-energy dependence of the Re(+) + O2 reaction is examined using guided ion-beam mass spectrometry. The cross section for ReO(+) formation from ground state Re(+) ((7)S) is unusual, exhibiting two endothermic features. The kinetic energy dependence for ReO(+) formation is analyzed to determine D0(Re(+)-O) = 4.82 ± 0.05 eV, with the higher energy feature having a threshold 1.35 ± 0.28 eV higher in energy. This bond energy is consistent with much less precise values determined in the literature. Formation of ReO2(+) is also observed with a pressure dependent cross section, establishing that it is formed in an exothermic reaction of ReO(+) with O2. The nature of the bonding for ReO(+) and ReO2(+) is discussed and analyzed primarily using theoretical calculations at the B3LYP/def2-TZVPPD level of theory. The ground state of ReO(+) is identified as either (5)? or (3)?, with the latter favored once estimates of spin-orbit splitting are included. Bond energies for ground state ReO(+) are calculated at this level as well as BP86 and CCSD(T,full) levels using several different basis sets. BP86 theoretical bond energies are higher than the experimental value, whereas B3LYP and CCSD(T,full) values are lower, although estimated spin-orbit corrections increase the latter close to experiment. Potential energy surfaces for the reaction of Re(+) with O2 are also calculated at the B3LYP/def2-TZVPPD level of theory and reveal that ground state Re(+) ((7)S) inserts into O2 by forming a Re(+)(O2) ((5)A") complex which can then couple with additional surfaces to form ground state ReO2(+) ((3)B1). Several explanations for the unusual dual endothermic features are explored, with no unambiguous explanation being evident. As such, this heavy metal system provides a very interesting experimental phenomenon of both adiabatic and nonadiabatic behavior. PMID:24006995

Armentrout, P B

2013-08-28

350

The bond energy of ReO+: Guided ion-beam and theoretical studies of the reaction of Re+ (7S) with O2  

NASA Astrophysics Data System (ADS)

The kinetic-energy dependence of the Re+ + O2 reaction is examined using guided ion-beam mass spectrometry. The cross section for ReO+ formation from ground state Re+ (7S) is unusual, exhibiting two endothermic features. The kinetic energy dependence for ReO+ formation is analyzed to determine D0(Re+-O) = 4.82 +/- 0.05 eV, with the higher energy feature having a threshold 1.35 +/- 0.28 eV higher in energy. This bond energy is consistent with much less precise values determined in the literature. Formation of ReO2+ is also observed with a pressure dependent cross section, establishing that it is formed in an exothermic reaction of ReO+ with O2. The nature of the bonding for ReO+ and ReO2+ is discussed and analyzed primarily using theoretical calculations at the B3LYP/def2-TZVPPD level of theory. The ground state of ReO+ is identified as either 5? or 3?, with the latter favored once estimates of spin-orbit splitting are included. Bond energies for ground state ReO+ are calculated at this level as well as BP86 and CCSD(T,full) levels using several different basis sets. BP86 theoretical bond energies are higher than the experimental value, whereas B3LYP and CCSD(T,full) values are lower, although estimated spin-orbit corrections increase the latter close to experiment. Potential energy surfaces for the reaction of Re+ with O2 are also calculated at the B3LYP/def2-TZVPPD level of theory and reveal that ground state Re+ (7S) inserts into O2 by forming a Re+(O2) (5A'') complex which can then couple with additional surfaces to form ground state ReO2+ (3B1). Several explanations for the unusual dual endothermic features are explored, with no unambiguous explanation being evident. As such, this heavy metal system provides a very interesting experimental phenomenon of both adiabatic and nonadiabatic behavior.

Armentrout, P. B.

2013-08-01

351

High-accuracy coupled-cluster computations of bond dissociation energies in SH, H2S, and H2O  

NASA Astrophysics Data System (ADS)

The first and second bond dissociation enthalpies of H2S have been investigated at up to the CCSD(T)/aug-ccpV6Z level of theory. Corrections for core/valence electron correlation, anharmonic zero point vibrational energy and relativistic effects were followed by extrapolation to the complete basis set limit. Analysis of direct dissociation yields D0)(S-H=349.9 and D0)(HS-H=375.8 kJ mol-1. Together these imply an atomization enthalpy for H2S about 1 kJ mol-1 larger than literature evaluations. Consideration of exchange of a second H atom from OH to SH yields D0)(HS-H=376.2 kJ mol-1. The two computations of D0)(HS-H lie within 0.5 kJ mol-1 of a recent spectroscopic measurement of D0)(HS-H=376.24plus-or-minus0.05 kJ mol-1 [R. C. Shiell, X. K. Hu, Q. J. Hu, and J. W. Hepburn, J. Phys. Chem. A 104, 4339 (2000)]. The deuterated analogs SD and D2S are also considered. There is also accord to within 1.5 kJ mol-1 with D0)(S-H=348.4plus-or-minus0.8 kJ mol-1, which we derive from the experimental literature. We propose revised enthalpies of formation, Delta]fH0(2[Pi]3/2)SH=142.6[plus-or-minus0.8 kJ mol-1 and Delta]fH298.15)(SH=143.1[plus-or-minus0.8 kJ mol-1. The results suggest the dominant uncertainties in these high-level calculations come from the basis set extrapolation and scalar relativistic terms, and that both contribute about 1 kJ mol-1 uncertainty. We also obtain D0)(H-OH=492.6 kJ mol-1, which compares well with recent experiments.

Peebles, Lynda R.; Marshall, Paul

2002-08-01

352

Methodology for hardware\\/software co-verification in C\\/C++  

Microsoft Academic Search

In this paper we present our C\\/C++-based design environment for hardware\\/software co-verification. Our approach is to use C\\/C++ to describe both hardware and software throughout the design flow. Our methodology supports the efficient mapping of C\\/C++ functional descriptions directly into hardware and software. The advantages of a C\\/C++-based flow from the verification point of view are presented. The use of

Luc Séméria; Abhijit Ghosh

2000-01-01

353

Theoretical Prediction of the Heats of Formation of C?H?O? Radicals Derived from Ethanol and of the Kinetics of ?-C-C Scission in the Ethoxy Radical  

SciTech Connect

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Thermochemical parameters of three C?H?O? radicals derived from ethanol were reevaluated using coupledcluster theory CCSD(T) calculations, with the aug-cc-pVnZ (n = D, T, Q) basis sets, that allow the CC energies to be extrapolated at the CBS limit. Theoretical results obtained for methanol and two CH?O? radicals were found to agree within ±0.5 kcal/mol with the experiment values. A set of consistent values was determined for ethanol and its radicals: (a) heats of formation (298 K) ?Hf(C?H?OH) = -56.4 ±0.8 kcal/mol (exptl: -56.21 ± 0.12 kcal/mol), ?Hf(CH?C?HOH) = -13.1 ±0.8 kcal/mol, ?Hf(C?H?CH?OH) = -6.2 ±0.8 kcal/mol, and ?Hf(CH?CH?O?) = -2.7 ± 0.8 kcal/mol; (b) bond dissociation energies (BDEs) of ethanol (0 K) BDE(CH?CHOH-H) = 93.9 ± 0.8 kcal/mol, BDE(CH?CH?OH-H) = 100.6 ± 0.8 kcal/mol, and BDE- (CH?CH?O-H) = 104.5 ± 0.8 kcal/mol. The present results support the experimental ionization energies and electron affinities of the radicals, and appearance energy of (CH?CHOH+) cation. ?-C-C bond scission in the ethoxy radical, CH?CH?O?, leading to the formation of C?H? and CH?=O, is characterized by a C-C bond energy of 9.6 kcal/mol at 0 K, a zero-point-corrected energy barrier of E0 ‡ = 17.2 kcal/mol, an activation energy of Ea = 18.0 kcal/mol and a high-pressure thermal rate coefficient of k?(298 K) = 3.9 s-1, including a tunneling correction. The latter value is in excellent agreement with the value of 5.2 s-1 from the most recent experimental kinetic data. Using RRKM theory, we obtain a general rate expression of k(T,p) = 1.26 x 109p0.793 exp(-15.5/RT) s-1 in the temperature range (T) from 198 to 1998 K and pressure range (p) from 0.1 to 8360.1 Torr with N? as the collision partners, where k(298 K, 760 Torr) = 2.7 s-1, without tunneling and k = 3.2 s-1 with the tunneling correction. Evidence is provided that heavy atom tunneling can play a role in the rate constant for ?-C-C bond scission in alkoxy radicals.

Matus, Myrna H.; Nguyen, Minh T.; Dixon, David A.

2007-01-11

354

Indium-mediated intermolecular alkyl radical addition to electron-deficient C [double bond] N bond and C [double bond] C bond in water.  

PubMed

[reaction: see text] The intermolecular alkyl radical addition to imine derivatives was studied in aqueous media by using indium as a single-electron-transfer radical initiator. The one-pot reaction based on radical addition to glyoxylic hydrazone provided a convenient method for preparing the alpha-amino acids. The indium-mediated radical addition to an electron-deficient C=C bond also proceeded effectively to provide the new carbon-carbon bond-forming method in aqueous media. PMID:11772108

Miyabe, Hideto; Ueda, Masafumi; Nishimura, Azusa; Naito, Takeaki

2002-01-10

355

Guided ion-beam studies of the reactions of Co(n)+ (n=2-20) with O2: cobalt cluster-oxide and -dioxide bond energies.  

PubMed

The kinetic-energy dependence for the reactions of Co(n)+ (n=2-20) with O2 is measured as a function of kinetic energy over a range of 0 to 10 eV in a guided ion-beam tandem mass spectrometer. A variety of Co(m)+, Co(m)O+, and Co(m)O2+ (m < or = n) product ions is observed, with the dioxide cluster ions dominating the products for all larger clusters. Reaction efficiencies of Co(n)+ cations with O2 are near unity for all but the dimer. Bond dissociation energies for both cobalt cluster oxides and dioxides are derived from threshold analysis of the energy dependence of the endothermic reactions using several different methods. These values show little dependence on cluster size for clusters larger than three atoms. The trends in this thermochemistry and the stabilities of oxygenated cobalt clusters are discussed. The bond energies of Co(n)+-O for larger clusters are found to be very close to the value for desorption of atomic oxygen from bulk-phase cobalt. Rate constants for O2 chemisorption on the cationic clusters are compared with results from previous work on cationic, anionic, and neutral cobalt clusters. PMID:16122305

Liu, Fuyi; Li, Feng-Xia; Armentrout, P B

2005-08-01

356

Determination and Interrelation of Bond Heterolysis and Homolysis Energies in Solution. Final Report, January 1988-August 1991.  

National Technical Information Service (NTIS)

Solution phase heats of heterolysis Delta H(sub(het)) and homolysis Delta H(sub(homo)) were determined for covalent bonds that can be cleaved to produce resonance-stabilized carbenium ions, anions, and radicals. Simple and broadly applicable correlation e...

E. M. Arnett

1993-01-01

357

The Dissociation Energies of CH4 and C2H2 Revisited  

NASA Technical Reports Server (NTRS)

The bond dissociation energies of CH4 and C2H2 and their fragments are investigated using basis set extrapolations and high levels of correlation. The computed bond dissociation energies (D(sub e)) are accurate to within 0.2 kcal/mol. The agreement with the experimental (D(sub 0)) values is excellent if we assume that the zero-point energy of C2H is 9.18 kcal/mol. The effect of core (1s) correlation on the bond dissociation energies of C-H bonds is shown to vary from 0.2 to 0.7 kcal/mol and that for C-C bonds varies from 0.4 to 2.2 kcal/mol.

Partridge, Harry; Bauschlicher, Charles W., Jr.; Langhoff, Stephen R. (Technical Monitor)

1995-01-01

358

Effect of C.C.C. [2-(chloroethyl)] trimethyl ammonium chloride on growth and sporulation in Fusarium oxysporum f. udum (butl.) Sn. et H.  

PubMed

In Fusarium oxysporum f. udum sporulation of macroconidia was completely inhibited due to the influence of C.C.C. [2-(Chloroethyl)] trimethyl ammonium chloride). Microconidial proliferation, on the other hand, was adversely affected and with increase in concentration of this compound a parallel and proportional decrease in the amount of microconidia was found. Size of microconidia, too, showed a concomitant decline. Although the size of the chlamydospores was also reduced, a tremendous increase in its population was evident, showing a positive response in favour of C.C.C. addition. Fungal mat accumulation, another important aspect of growth, did not evince any inhibitory pattern, compared to the progressive increase in C.C.C. amoung in younger cultures. In older cultures (15-day old), an initial depressing shock of C.C.C. addition could be seen. However, after stepwise and gradual adjustment to the new environment the same positive response of mycelial growth was discernible, although in a less degree than that of the young cultures. PMID:664938

Prasad, M; Chaudhary, S K

1978-01-01

359

Highly functionalized pyridines synthesis from N-sulfonyl ketimines and alkynes using the N-S bond as an internal oxidant.  

PubMed

The N-S bond-based internal oxidant offers a distinct approach for the synthesis of highly functionalized pyridines. A novel Rh(III)-catalyzed one-pot process undergoes an efficient C-C/C-N bond formation along with desulfonylation under very mild conditions. The method is quite simple, general, and efficient. PMID:24597609

Zhang, Qian-Ru; Huang, Ji-Rong; Zhang, Wei; Dong, Lin

2014-03-21

360

Effects of lead design on ultrasonic bond quality of wire bonds  

Microsoft Academic Search

Wire bonding is an important method of interconnection in microelectronics. The micro welding of the contact pad to the gold wire is achieved by a thermosonic wire bonding process. Ultrasonic energy is known to soften metallic materials and hence when used in the wire bond process to decrease the flow stress similar to thermal energy. But experimental results shows for

Narasimalu Srikanth; C. J. Vath

2005-01-01

361

Reactions of fourth-period metal ions (Ca sup + endash Zn sup + ) with O sub 2 : Metal-oxide ion bond energies  

SciTech Connect

Reactions of Ca{sup +}, Zn{sup +} and all first-row atomic transition metal ions with O{sub 2} are studied using guided ion beam techniques. While reactions of the ground states of Sc{sup +}, Ti{sup +}, and V{sup +} are exothermic, the remaining metal ions react with O{sub 2} in endothermic processes. Analyses of these endothermic reactions provide new determinations of the M{sup +}--O bond energies for these eight elements. Source conditions are varied such that the contributions of excited states of the metal ions can be explicitly considered for Mn{sup +}, Co{sup +}, Ni{sup +}, and Cu{sup +}. Results (in eV) at 0 K are {ital D}{sup 0}(Ca{sup +}--O)=3.57{plus minus}0.05, {ital D}{sup 0}(Cr{sup +}--O)=3.72{plus minus}0.12, {ital D}{sup 0}(Mn{sup +}--O)=2.95{plus minus}0.13, {ital D}{sup 0}(Fe{sup +}--O)=3.53{plus minus}0.06 (reported previously), {ital D}{sup 0}(Co{sup +}--O)=3.32{plus minus}0.06, {ital D}{sup 0}(Ni{sup +}--O)=2.74{plus minus}0.07, {ital D}{sup 0}(Cu{sup +}--O)=1.62{plus minus}0.15, and {ital D}{sup 0}(Zn{sup +}--O)=1.65{plus minus}0.12. These values along with literature data for neutral metal oxide bond energies and ionization energies are critically evaluated. Periodic trends in the ionic metal oxide bond energies are compared with those of the neutral metal oxides and those of other related molecules.

Fisher, E.R.; Elkind, J.L.; Clemmer, D.E.; Georgiadis, R.; Loh, S.K.; Aristov, N.; Sunderlin, L.S.; Armentrout, P.B. (Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (USA) Department of Chemistry, University of California, Berkeley, CA (USA))

1990-08-15

362

Observation of B+??¯c0?c+ and evidence for B0??¯c-?c+  

NASA Astrophysics Data System (ADS)

We report the first observation of the decay B+??¯c0?c+ with a significance of 8.7? and evidence for the decay B0??¯c-?c+ with a significance of 3.8?. The product B(B+??¯c0?c+)×B(?¯c0??¯+?-) is measured to be (4.8-0.9+1.0±1.1±1.2)×10-5, and B(B0??¯c-?c+)×B(?¯c-??¯+?-?-) is measured to be (9.3-2.8+3.7±1.9±2.4)×10-5. The errors are statistical, systematic and the error of the ?c+?pK-?+ branching fraction, respectively. The decay B+??¯c0?c+ is the first example of a two-body exclusive B+ decay into two charmed baryons. The data used for this analysis was accumulated at the ?(4S) resonance, using the Belle detector at the e+e- asymmetric-energy collider KEKB. The integrated luminosity of the data sample is equal to 357fb-1, corresponding to 386×106 BB¯ pairs.

Chistov, R.; Abe, K.; Adachi, I.; Aihara, H.; Anipko, D.; Arinstein, K.; Asano, Y.; Aulchenko, V.; Aushev, T.; Bahinipati, S.; Bakich, A. M.; Balagura, V.; Bedny, I.; Bitenc, U.; Bizjak, I.; Bondar, A.; Bozek, A.; Bra?ko, M.; Brodzicka, J.; Browder, T. E.; Chao, Y.; Chen, A.; Chen, W. T.; Cheon, B. G.; Choi, S.-K.; Choi, Y.; Choi, Y. K.; Chuvikov, A.; Cole, S.; Dalseno, J.; Danilov, M.; Dash, M.; Drutskoy, A.; Eidelman, S.; Epifanov, D.; Fratina, S.; Gabyshev, N.; Garmash, A.; Gershon, T.; Go, A.; Golob, B.; Gorišek, A.; Ha, H. C.; Haba, J.; Hayasaka, K.; Hayashii, H.; Hazumi, M.; Hokuue, T.; Hoshi, Y.; Hou, S.; Hou, W.-S.; Iijima, T.; Ishikawa, A.; Iwasaki, M.; Iwasaki, Y.; Kapusta, P.; Katayama, N.; Kawasaki, T.; Khan, H. R.; Kichimi, H.; Kim, H. J.; Kim, S. M.; Kinoshita, K.; Korpar, S.; Krokovny, P.; Kulasiri, R.; Kuo, C. C.; Kuzmin, A.; Kwon, Y.-J.; Leder, G.; Lesiak, T.; Lin, S.-W.; Liventsev, D.; MacNaughton, J.; Majumder, G.; Mandl, F.; Matsumoto, T.; Mitaroff, W.; Miyake, H.; Miyata, H.; Miyazaki, Y.; Mizuk, R.; Mueller, J.; Nagasaka, Y.; Nakano, E.; Nakao, M.; Nishida, S.; Ogawa, S.; Ohshima, T.; Okuno, S.; Olsen, S. L.; Onuki, Y.; Ostrowicz, W.; Ozaki, H.; Pakhlov, P.; Palka, H.; Park, H.; Park, K. S.; Peak, L. S.; Pestotnik, R.; Piilonen, L. E.; Poluektov, A.; Sakai, Y.; Sato, N.; Satoyama, N.; Schietinger, T.; Schneider, O.; Senyo, K.; Sevior, M. E.; Shwartz, B.; Sidorov, V.; Somov, A.; Stamen, R.; Stani?, S.; Stari?, M.; Sumiyoshi, T.; Suzuki, S. Y.; Takasaki, F.; Tamura, N.; Tanaka, M.; Taylor, G. N.; Teramoto, Y.; Tian, X. C.; Tsukamoto, T.; Uehara, S.; Uglov, T.; Ueno, K.; Unno, Y.; Uno, S.; Usov, Y.; Varner, G.; Varvell, K. E.; Villa, S.; Wang, C. C.; Wang, C. H.; Wang, M.-Z.; Won, E.; Xie, Q. L.; Yamaguchi, A.; Yamashita, Y.; Yamauchi, M.; Zhang, C. C.; Zhang, J.; Zhang, L. M.; Zhang, Z. P.; Zhilich, V.

2006-12-01

363

Ablation properties of C/C-SiC composites tested on an arc heater  

NASA Astrophysics Data System (ADS)

Carbon fiber-reinforced carbon and silicon carbide (C/C-SiC) composites were fabricated by a combination of chemical vapor infiltration and liquid silicon infiltration. Ablation properties of C/C-SiC composites and C/C composites with similar technique were tested on a high-pressure arc heater. The results show that ablation properties of C/C-SiC composites are more severe than those of C/C composites. Ablation of C/C-SiC composites includes oxidation, sublimation of SiC (Si), and mechanical denudation. Oxidation and sublimation of SiC (Si) lead to the enlarged ablation rates between carbon fibers and matrices, which finally cause serious ablation of C/C-SiC composites.

Yin, Jian; Zhang, Hongbo; Xiong, Xiang; Zuo, Jinglv; Tao, Huijin

2011-11-01

364

The enthalpy of formation of fullerene fluoride C60F18 and the C-F bond energy  

NASA Astrophysics Data System (ADS)

The enthalpy of combustion of crystalline fullerene fluoride C60F18 was determined in an isoperibolic calorimeter with a rotating platinized bomb, and the enthalpy of formation of the compound was calculated. The enthalpy of sublimation of C60F18 measured earlier was used to calculate the enthalpy of formation of fullerene fluoride in the gas phase and the mean enthalpy of dissociation of C-F bonds in this compound.

Papina, T. S.; Luk'yanova, V. A.; Goryunkov, A. A.; Ioffe, I. N.; Gol'Dt, I. V.; Buyanovskaya, A. G.; Kabaeva, N. M.; Sidorov, L. N.

2007-10-01

365

Ultrasonic bonding of polymer microfluidic chips  

Microsoft Academic Search

Bonding is an essential step to enclose microchannels or microchambers in lab-on-a-chip. Ultrasonic bonding was studied as a deformation-free technique to realize high efficiency bonding of microfluidic chips. Based on viscoelastic dissipation theory, the main influential factors of heat generation rate during ultrasonic bonding was theoretically analyzed and numerically calculated using finite element method. According to the results, micro energy

Zong-bo Zhang; Yi Luo; Xiao-dong Wang; Zhen-qiang Zhang; Li-ding Wang

2008-01-01

366

Hexacoordinate bonding and aromaticity in silicon phthalocyanine.  

PubMed

Si-E bondings in hexacoordinate silicon phthalocyanine were analyzed using bond order (BO), energy partition, atoms in molecules (AIM), electron localization function (ELF), and localized orbital locator (LOL). Bond models were proposed to explain differences between hexacoordinate and tetracoordinate Si-E bondings. Aromaticity of silicon phthalocyanine was investigated using nucleus-independent chemical shift (NICS), harmonic oscillator model of aromaticity (HOMA), conceptual density functional theory (DFT), ring critical point (RCP) descriptors, and delocalization index (DI). Structure, energy, bonding, and aromaticity of tetracoordinate silicon phthalocyanine were studied and compared with hexacoordinate one. PMID:21105726

Yang, Yang

2010-12-23

367

Selective activation of carbon-carbon bonds next to a carbonyl group  

NASA Astrophysics Data System (ADS)

ORGANOMETALLIC complexes are used to effect a wide range of catalytic transformations in organic synthesis, such as the activation of C-H bonds1,2. Carbon-carbon bonds, however, are generally unreactive towards transition metals under homogeneous conditions. C-C bond activation by a process of oxidative addition to soluble transition-metal complexes has been limited mostly to stoichiometric (not catalytic) reactions1,3-7,18, to highly strained substrates such as cyclopropane and cubane1,8-11 or to chelating ketones19. Here we present a synthetically useful process of selective C-C bond activation in which the C-C bond adjacent to a carbonyl group is opened by insertion of a soluble rhodium(I) complex. The resulting organometallic intermediate can be transformed to a variety of products in a way that regenerates the rhodium complex. We anticipate that this catalytic scheme will have considerable utility in organic synthesis.

Murakami, Masahiro; Amii, Hideki; Ito, Yoshihiko

1994-08-01

368

Hydrogen Bonded Arrays: The Power of Multiple Hydrogen Bonds  

SciTech Connect

Hydrogen bond interactions in small covalent model compounds (i.e. deprotonated polyhydroxy alcohols) were measured by negative ion photoelectron spectroscopy. The experimentally determined vertical and adiabatic electron detachment energies for (HOCH2CH2)2CHO (2a), (HOCH2CH2) 3CO (3a) and (HOCH2CH2CH(OH)CH2)3CO (4a) reveal that hydrogen-bonded networks can provide enormous stabilizations, and that a single charge center not only can be stabilized by up to 3 hydrogen bonds but it can increase the interaction energy between non-charged OH groups by 5.8 kcal mol1 or more per hydrogen bond. This can lead to pKa values that are very different than in water, and provide some of the impetus for catalytic processes.

Shokri, Alireza; Schmidt, Jacob C.; Wang, Xue B.; Kass, Steven R.

2012-02-01

369

Highly Accurate CCSD(T) and DFT–SAPT Stabilization Energies of H-Bonded and Stacked Structures of the Uracil Dimer  

SciTech Connect

The CCSD(T) interaction energies for the H-bonded and stacked structures of the uracil dimer are determined at the aug-cc-pVDZ and aug-cc-pVTZ levels. On the basis of these calculations we can construct the CCSD(T) interaction energies at the complete basis set (CBS) limit. The most accurate energies, based either on direct extrapolation of the CCSD(T) correlation energies obtained with the aug-cc-pVDZ and aug-cc-pVTZ basis sets or on the sum of extrapolated MP2 interaction energies (from aug-cc-pVTZ and aug-cc-pVQZ basis sets) and extrapolated ?CCSD(T) correction terms [difference between CCSD(T) and MP2 interaction energies] differ only slightly, which demonstrates the reliability and robustness of both techniques. The latter values, which represent new standards for the H-bonding and stacking structures of the uracil dimer, differ from the previously published data for the S22 set by a small amount. This suggests that interaction energies of the S22 set are generated with chemical accuracy. The most accurate CCSD(T)/CBS interaction energies are compared with interaction energies obtained from various computational procedures, namely the SCS–MP2 (SCS: spin-component-scaled), SCS(MI)–MP2 (MI: molecular interaction), MP3, dispersion-augmented DFT (DFT–D), M06–2X, and DFT–SAPT (SAPT: symmetry-adapted perturbation theory) methods. Among these techniques, the best results are obtained with the SCS(MI)–MP2 method. Remarkably good binding energies are also obtained with the DFT–SAPT method. Both DFT techniques tested yield similarly good interaction energies. The large magnitude of the stacking energy for the uracil dimer, compared to that of the benzene dimer, is explained by attractive electrostatic interactions present in the stacked uracil dimer. These interactions force both subsystems to approach each other and the dispersion energy benefits from a shorter intersystem separation.

Pitonak, Michal; Riley, Kevin E.; Neogrady, Pavel; Hobza, Pavel

2008-06-23

370

Guided ion-beam studies of the kinetic-energy-dependent reactions of Co(n)+ (n = 2-16) with D2: cobalt cluster-deuteride bond energies.  

PubMed

The kinetic-energy-dependent cross sections for the reactions of Co(n)+ (n = 2-16) with D2 are measured as a function of kinetic energy over a range of 0-8 eV in a guided ion-beam tandem mass spectrometer. The observed products are Co(n) D+ for all clusters and Co(n)D2+ for n = 4,5,9-16. Reactions for the formation of Co(n)D+ (n = 2-16) and Co9D2+ are observed to exhibit thresholds, whereas cross sections for the formation of Co(n)D2+ (n = 4,5,10-16) exhibit exothermic reaction behavior. The Co(n)+-D bond energies as a function of cluster size are derived from the threshold analysis of the kinetic-energy dependence of the endothermic reactions and are compared to previously determined metal-metal bond energies, D0(Co(n)+-Co). The bond energies of Co(n)+-D generally increase as the cluster size increases, and roughly parallel those for Co(n)+-Co for clusters n > or = 4. These trends are explained in terms of electronic and geometric structures for the Co(n)+ clusters. The bond energies of Co(n)+-D for larger clusters (n > or = 10) are found to be very close to the value for chemisorption of atomic hydrogen on bulk-phase cobalt. The rate constants for D2 chemisorption on the cationic clusters are compared with the results from previous work on cationic and neutral cobalt clusters. PMID:16161586

Liu, Fuyi; Armentrout, P B

2005-05-15

371

Theoretical study of GeH sub n , AsH sub n , and SeH sub n : Bond dissociation energies  

SciTech Connect

{ital Ab} {ital initio} molecular orbital theory (Moller--Plesset perturbation theory to fourth order and new basis sets developed for Ge, As, and Se) is used to calculate the atomization energies of GeH{sub {ital n}}({ital n}=1--4), AsH{sub {ital n}}({ital n}=1--3), and SeH{sub {ital n}}({ital n}=1--2). Good agreement is found with the experimental bond dissociation energies of these hydrides derived from recent photoionization studies. The theoretical energies are combined with experimental data on the isolated atoms to determine ideal enthalpies of formation at 0 K for these hydrides, which are expected to have an accuracy of about {plus minus}3 kcal/mol ({plus minus}0.15 eV).

Binning, R.C. Jr. (Department of Chemistry and Physics, Carlow College, Pittsburgh, Pennsylvania 15213 (USA)); Curtiss, L.A. (Chemical Technology Division/Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439-4837 (USA))

1990-02-01

372

Collision-induced dissociation of Ti sup + sub n ( n =2--22) with Xe: Bond energies, geometric structures, and dissociation pathways  

SciTech Connect

The kinetic energy dependence of the collision-induced dissociation (CID) of Ti{sup +}{sub {ital n}} ({ital n}=2--22) with Xe is studied by using a guided ion beam mass spectrometer. Examination of the CID cross section behavior over a broad collision energy range demonstrates that Ti{sup +}{sub {ital n}} clusters dissociate exclusively by sequential loss of Ti atoms. Bond energies of ionic titanium clusters, {ital D}{sup 0}(Ti{sup +}{sub {ital n}{minus}1}--Ti), are determined from measurements of the CID thresholds. {ital D}{sup 0}(Ti{sup +}{sub {ital n}{minus}1}--Ti) are found to change significantly as a function of cluster size, with local maxima at {ital n}=7, 13, and 19. This pattern of highly stable cluster ions suggests that titanium cluster ions favor icosahedral structures.

Lian, L.; Su, C.; Armentrout, P.B. (Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States))

1992-09-15

373

Gas-phase photodissociation of FeCH/sub 2//sup +/ and CoCH/sub 2//sup +/: determination of the carbide, carbyne, and carbene bond energies  

SciTech Connect

Photodissociation of MCH/sub 2//sup +/ (M = Fe, Co) is observed to yield three products M/sup +/, MC/sup +/, and MCH/sup +/. This result is in contrast to the low-energy collision-induced dissociation of MCH/sub 2//sup +/, which yields M/sup +/ exclusively. From the photoappearance thresholds of the products, the following bond energies are assigned: D/sup 0/(Co/sup +/-CH/sub 2/) = 84 +/- 5 kcal/mol, D/sup 0/(Co/sup +/-CH) = 100 +/- 7 kcal/mol, D/sup 0/(Co/sup +/-C) = 90 +/- 7 kcal/mol, D/sup 0/(Fe/sup +/-CH/sub 2/) = 82 +/- 5 kcal/mol, D/sup 0/(Fe/sup +/-CH) = 101 +/- 7kcal/mol, and D/sup 0/(Fe/sup +/-C) = 94 +/- 7 kcal/mol. Compared to the results of an earlier ion-beam study, the Co/sup +/-CH/sub 2/ bond energy reported here is in excellent agreement while the Fe/sup +/-CH/sub 2/ value is significantly lower.

Hettich, R.L.; Freiser, B.S.

1986-05-14

374

Estimation of the energy of coordination K-O bonds in a potassium hydrophthalate crystal on the basis of electron-density distribution analysis  

SciTech Connect

Detailed study of the nature of weak coordination K-O interactions and strong O-H{center_dot}{center_dot}{center_dot}O hydrogen bonds and estimation of their energy in a potassium hydrophthalate crystal have been performed on the basis of the topological analysis of the electron density distribution function, obtained from precise X-ray diffraction study at 100 K (R1 = 0.0110), within Bader's 'Atoms in Molecule' theory. It is shown that the charge transfer accompanying the formation of cation{center_dot}{center_dot}{center_dot}anion associates in the crystal is only 0.05 e.

Nelyubina, Yu. V., E-mail: kostya@xray.ineos.ac.ru; Lyssenko, K. A.; Antipin, M. Yu. [Russian Academy of Sciences, Nesmeyanov Institute of Organoelement Compounds (Russian Federation)

2008-03-15

375

Estimation of the energy of coordination K-O bonds in a potassium hydrophthalate crystal on the basis of electron-density distribution analysis  

SciTech Connect

Detailed study of the nature of weak coordination K-O interactions and strong O-H...O hydrogen bonds and estimation of their energy in a potassium hydrophthalate crystal have been performed on the basis of the topological analysis of the electron density distribution function, obtained from precise X-ray diffraction study at 100 K (R1 = 0.0110), within Bader's 'Atoms in Molecule' theory. It is shown that the charge transfer accompanying the formation of cation...anion associates in the crystal is only 0.05 e.

Nelyubina, Yu. V., E-mail: kostya@xray.ineos.ac.ru; Lyssenko, K. A.; Antipin, M. Yu. [Russian Academy of Sciences, Nesmeyanov Institute of Organoelement Compounds (Russian Federation)

2008-03-15

376

Tests of the RPBE, revPBE, ?-HCTHhyb, ?B97X-D, and MOHLYP density functional approximations and 29 others against representative databases for diverse bond energies and barrier heights in catalysis  

NASA Astrophysics Data System (ADS)

Thirty four density functional approximations are tested against two diverse databases, one with 18 bond energies and one with 24 barriers. These two databases are chosen to include bond energies and barrier heights which are relevant to catalysis, and in particular the bond energy database includes metal-metal bonds, metal-ligand bonds, alkyl bond dissociation energies, and atomization energies of small main group molecules. Two revised versions of the Perdew-Burke-Ernzerhof (PBE) functional, namely the RPBE and revPBE functionals, widely used for catalysis, do improve the performance of PBE against the two diverse databases, but give worse results than B3LYP (which denotes the combination of Becke's 3-parameter hybrid treatment with Lee-Yang-Parr correlation functional). Our results show that the Minnesota functionals, M05, M06, and M06-L give the best performance for the two diverse databases, which suggests that they deserve more attention for applications to catalysis. We also obtain notably good performance with the ?-HCTHhyb, ?B97X-D, and MOHLYP functional (where MOHLYP denotes the combination of the OptX exchange functional as modified by Schultz, Zhao, and Truhlar with half of the LYP correlation functional).

Yang, Ke; Zheng, Jingjing; Zhao, Yan; Truhlar, Donald G.

2010-04-01

377

A mild route to mesoporous Mo2C-C hybrid nanospheres for high performance lithium-ion batteries  

NASA Astrophysics Data System (ADS)

In this work, we have developed a mild route to fabricate typically mesoporous Mo2C-C hybrid nanospheres based on a solvothermal synthesis and reduction-carbonization process. This work opens a low-temperature route to synthesize valuable carbides. The resultant Mo2C-C hybrid, for the first time, is used as an anode material in lithium ion batteries (LIBs). Compared with bulk Mo2C, the Mo2C-C hybrid exhibits much better electrochemical performance. Remarkably, the hybrid electrode can deliver a specific capacity of over 670 mA h g-1 after 50 cycles at 100 mA g-1, which is much higher than that of the bulk material (113 mA h g-1). Even cycled at a high current density of 1000 mA g-1, high capacities of around 400-470 mA h g-1 can still be retained for the Mo2C-C hybrid. It might benefit from the synergistic effect of the nanohybridization, effectively relieving the volume change during the repeated lithium insertion-extraction reactions and maintaining the integrity of the electrical connections. It is expected that the present synthesis strategy for the Mo2C-C hybrid can be extended to other nanostructured carbides with good energy storage performance.In this work, we have developed a mild route to fabricate typically mesoporous Mo2C-C hybrid nanospheres based on a solvothermal synthesis and reduction-carbonization process. This work opens a low-temperature route to synthesize valuable carbides. The resultant Mo2C-C hybrid, for the first time, is used as an anode material in lithium ion batteries (LIBs). Compared with bulk Mo2C, the Mo2C-C hybrid exhibits much better electrochemical performance. Remarkably, the hybrid electrode can deliver a specific capacity of over 670 mA h g-1 after 50 cycles at 100 mA g-1, which is much higher than that of the bulk material (113 mA h g-1). Even cycled at a high current density of 1000 mA g-1, high capacities of around 400-470 mA h g-1 can still be retained for the Mo2C-C hybrid. It might benefit from the synergistic effect of the nanohybridization, effectively relieving the volume change during the repeated lithium insertion-extraction reactions and maintaining the integrity of the electrical connections. It is expected that the present synthesis strategy for the Mo2C-C hybrid can be extended to other nanostructured carbides with good energy storage performance. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr06678a

Gao, Qing; Zhao, Xinyu; Xiao, Ying; Zhao, Di; Cao, Minhua

2014-05-01

378

Pitting corrosion resistance of high nitrogen f.c.c. phase in plasma source ion nitrided austenitic stainless steel  

Microsoft Academic Search

Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for low-energy implanting nitrogen ions and then diffusing them into metal and alloy. In this work, 1Cr18Ni9Ti (18-8 type) austenitic stainless steel was treated at a process temperature of 380°C during a nitriding period of 4 h. A single high nitrogen f.c.c. phase (?N) with a high nitrogen

X. M. Zhu; M. K. Lei

2000-01-01

379

C-H bond activation as the initial step in the Co sup + -mediated demethanation of propane: The critical role of angular momentum at the rate-limiting transition state  

SciTech Connect

Exothermic reactions of transition-metal ions with alkanes have in many instances been shown to be facile in the gas phase. Reactions mainly result in the loss of molecular hydrogen and small alkanes to yield metal ion-olefin complexes. A variety of experimental techniques have provided thermochemical, kinetic, dynamic, and mechanistic information for these reactions, with an important focus being the identification of the initial activation step. The question of C-H versus C-C bond activation as the initial step in the formation of C-C bond cleavage products has yet to be resolved. The authors have measured reaction cross sections and kinetic energy release distributions for the exothermic reactions of Co{sup +} with propane, propane-2-d{sub 1}, propane-2,2-d{sub 2}, propane-1,1,1-d{sub 3}, propane-1,1,1,3,3,3-d{sub 6}, and propane-d{sub 8}.

van Koppen, P.A.M.; Brodbelt-Lustig, J.; Bowers, M.T. (Univ. of California, Santa Barbara (USA)); Dearden, D.V.; Beauchamp, J.L. (California Institute of Technology, Pasadena (USA)); Fisher, E.R.; Armentrout, P.B. (Univ. of Utah, Salt Lake City (USA))

1990-07-04

380

E2 strength in the radiative charmed baryon decay ? c? ? ? c?  

NASA Astrophysics Data System (ADS)

The radiative decay ? Q? ? ? Q? can have both magnetic dipole (M1) and electric quadrupole (E2) components. In the heavy quark limit MQ ? ? the transition arises from the spin of the light degrees of freedom changing from sl = 1 to sl = 0 and hence the E2 contribution vanishes. We compute the leading contribution to the E2 strength in chiral perturbation theory and find that the amplitude is enhanced by a small energy denominator in the chiral limit. This enhancement essentially compensates for the {1}/{M c} suppression that is present in the charm system. We find a mixing ratio of order a few percent dependent upon the ? c-? c? spin symmetry breaking mass difference. The analogous quantity in the b-baryon sector is smaller by a factor of ? {M c}/{M b}.

Savage, Martin J.

1995-02-01

381

Bonding in Beryllium Clusters  

NASA Astrophysics Data System (ADS)

Beryllium clusters provide an ideal series for exploring the evolution from discrete molecules to the metallic state. The beryllium dimer has a formal bond order of zero, but the molecule is weakly bound. In contrast, bulk-phase beryllium is a hard metal with a high melting point. Theoretical calculations indicate that the bond energies increase dramatically for Ben clusters in the range n=2-6. A triplet ground state is found for n=6, indicating an early emergence of metallic properties. There is an extensive body of theoretical work on smaller Ben clusters, in part because this light element can be treated using high-level methods. However, the apparent simplicity of beryllium is deceptive, and the calculations have proved to be challenging owing to strong electron correlation and configuration interaction effects. Consequently, these clusters have become benchmark systems for the evaluation of a wide spectrum of quantum chemistry methods.

Heaven, Michael C.; Merritt, Jeremy M.; Bondybey, Vladimir E.

2011-05-01

382

Stereochemistry of the intramolecular shift of the C-C bond in the reactions of cyclopropene compounds with electrophilic reagents  

SciTech Connect

The characteristic direction in the reactions of cyclopropene compounds with electrophilic reagents leads to the formation of acyclic products, which can in principle have the E and Z configurations. Earlier it was shown that the E isomer is formed preferentially in the reaction of 1-methylcyclopropene with bromine and almost exclusively in the reaction with N-bromosuccinimide. In the present communication the authors give stereochemical data on the reaction of 1-methylcyclopropene with deuterium chloride in CH/sub 3/COOD.

Kartashov, V.R.; Afanas'ev, P.S.; Skorobogatova, E.V.; Chertkov, V.A.; Ermolaeva, V.N.; Sergeev, N.M.; Zefirov, N.S.

1986-09-20

383

Influence of substituent effects on the formation of P···Cl pnicogen bonds or halogen bonds.  

PubMed

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out in search of equilibrium structures with P···Cl pnicogen bonds or halogen bonds on the potential energy surfaces H2FP:ClY for Y = F, NC, Cl, CN, CCH, CH3, and H. Three different types of halogen-bonded complexes with traditional, chlorine-shared, and ion-pair bonds have been identified. Two different pnicogen-bonded complexes have also been found on these surfaces. The most electronegative substituents F and NC form only halogen-bonded complexes, while the most electropositive substituents CH3 and H form only pnicogen-bonded complexes. The halogen-bonded complexes involving the less electronegative groups Cl and CN are more stable than the corresponding pnicogen-bonded complexes, while the pnicogen-bonded complexes with CCH are more stable than the corresponding halogen-bonded complex. Traditional halogen-bonded complexes are stabilized by charge transfer from the P lone pair to the Cl-A ?* orbital, where A is the atom of Y directly bonded to Cl. Charge transfer from the Cl lone pair to the P-F ?* orbital stabilizes pnicogen-bonded complexes. As a result, the H2FP unit becomes positively charged in halogen-bonded complexes and negatively charged in pnicogen-bonded complexes. Spin-spin coupling constants (1X)J(P-Cl) for complexes with traditional halogen bonds increase with decreasing P-Cl distance, reach a maximum value for complexes with chlorine-shared halogen bonds, and then decrease and change sign when the bond is an ion-pair bond. (1p)J(P-Cl) coupling constants across pnicogen bonds tend to increase with decreasing P-Cl distance. PMID:24641102

Del Bene, Janet E; Alkorta, Ibon; Elguero, José

2014-03-27

384

Solar Energy and Low Level Cyclic Energy Flow (20 to 100 exp 0 C) Storage as Chemical Bond Energy of Compounds Undergoing Thermal Decomposition. Final Report.  

National Technical Information Service (NTIS)

Various materials and reactions are studied for thermochemical heat storage at low temperatures for application in solar annual energy storage. Thermochemical reactions with water vapor were studied including selected hydrates and some adsorbents and mole...

J. Bougard P. Capron R. Jadot

1980-01-01

385

Halogen bonding (X-bonding): a biological perspective.  

PubMed

The concept of the halogen bond (or X-bond) has become recognized as contributing significantly to the specificity in recognition of a large class of halogenated compounds. The interaction is most easily understood as primarily an electrostatically driven molecular interaction, where an electropositive crown, or ?-hole, serves as a Lewis acid to attract a variety of electron-rich Lewis bases, in analogous fashion to a classic hydrogen bonding (H-bond) interaction. We present here a broad overview of X-bonds from the perspective of a biologist who may not be familiar with this recently rediscovered class of interactions and, consequently, may be interested in how they can be applied as a highly directional and specific component of the molecular toolbox. This overview includes a discussion for where X-bonds are found in biomolecular structures, and how their structure-energy relationships are studied experimentally and modeled computationally. In total, our understanding of these basic concepts will allow X-bonds to be incorporated into strategies for the rational design of new halogenated inhibitors against biomolecular targets or toward molecular engineering of new biological-based materials. PMID:23225628

Scholfield, Matthew R; Zanden, Crystal M Vander; Carter, Megan; Ho, P Shing

2013-02-01

386

Implementation of a Hamiliton-receptor-based hydrogen-bonding motif toward a new electron donor-acceptor prototype: electron versus energy transfer.  

PubMed

A new modular concept for the self-assembly of electron donor-acceptor complexes is presented that ensures (i) fine-tuning the strength of the complexation, (ii) controlling the electronic coupling to impact electron and energy transfer processes, and (iii) high solubility of the corresponding hybrid architectures. This task has been realized through developing a series of porphyrin-fullerene donor-acceptor systems held together by a Hamilton-receptor-based hydrogen-bonding motif. In this context, novel libraries of C60 monoadducts (1) containing cyanuric acid side chains and of tetraphenylporphyrin derivatives (2) involving the complementary Hamilton-receptor unit were synthesized. The association constants of the corresponding 1:1 complexes (1.2) connected by six hydrogen bonds were determined complementary by NMR and fluorescence assays. Their strength, which was found to be in the range between 3.7 x 10(3) and 7.9 x 10(5) M-1, depends on the nature of the spacers, namely, hexylene versus propylene chains. Finally, transient absorption studies revealed photoinduced electron transfer from ZnP to C60 in the corresponding 1.2 complexes, which generate radical ion pair states that are persistent well beyond the ns time scale. In the case of the analogous SnP complexes, energy instead of electron transfer was observed. This is due to the shift of oxidation potential caused by presence of Sn in the oxidation state of +4. PMID:18052376

Wessendorf, Florian; Gnichwitz, Jan-Frederik; Sarova, Ginka H; Hager, Kristine; Hartnagel, Uwe; Guldi, Dirk M; Hirsch, Andreas

2007-12-26

387

Influence of chlorine substitution on intramolecular hydrogen bond energy and ESIPT barrier: Experimental and theoretical measurements on the photophysics of 3,5-dichlorosalicylic acid  

NASA Astrophysics Data System (ADS)

The effect of chlorine atom on the intramolecular hydrogen bond strength and excited state proton transfer barrier in pharmaceutically important chloro-substituted derivative of salicylic acid viz., 3,5-dichlorosalicylic acid (3,5DCSA) has been explored through steady-state absorption, emission and time-resolved fluorescence spectroscopy. Stokes shifted emission band with negligible solvent polarity dependency corresponds to the spectroscopic signature of excited state intramolecular proton transfer (ESIPT) reaction. The spectral signature was compared with its parent molecule salicylic acid (SA) and 5-chlorosalicylic acid (5ClSA). Quantum chemical calculations by ab initio Hartree-Fock (HF) and Density Functional Theory (DFT) methods have been fruitfully employed to correlate experimental findings. Calculated S0 and S1 states potential energy surfaces across the proton transfer co-ordinate substantiates the experimental evidence for the occurrence of ESIPT process and negates the ground state intramolecular proton transfer (GSIPT) reaction. Weakening of intramolecular hydrogen bond (IMHB) energy and subsequent enhancement of barrier to ESIPT reaction in 3,5DCSA as compared to SA and 5ClSA appears to be a reflection of conjugate impact of electron withdrawing inductive and electron donating resonance effects of chlorine substitutions depending on its location on the aromatic benzene nucleus.

Paul, Bijan Kumar; Samanta, Anuva; Guchhait, Nikhil

2010-08-01

388

Controlled energy transfer between isolated donor-acceptor molecules intercalated in thermally self-ensemble two-dimensional hydrogen bonding cages  

NASA Astrophysics Data System (ADS)

Thermally assembled hydrogen bonding cages which are neither size nor guest specific have been developed using a poly (vinyl alcohol) (PVA) host. A water-soluble conjugated polymer poly(2,5-bis(3-sulfonatopropoxy)-1,4-phenylene, disodium salt-alt-1,4-phenylene) (PPP-OPSO3) as a donor and tris(2,2-bipyridyl)- ruthenium(II) [Ru(bpy)32+] as an acceptor have been isolated and trapped in such a PVA matrix network. This is a unique system that shows negligible exciton diffusion and the donor and acceptor predominantly interact by a direct single step excitation transfer process (DSSET). Singlet and triplet exciton quenching have been studied. Time-resolved fluorescence lifetime measurement at different acceptor concentrations has enabled us to determine the dimensionality of the energy-transfer process within the PVA scaffold. Our results reveal that the PVA hydrogen bonding network effectively isolates the donor-acceptor molecules in a two-dimensional layer structure (lamella) leading to the condition where a precise control of the energy and charge transfer is possible.

Al Attar, Hameed A.; Monkman, Andrew P.

2012-12-01

389

Unusual nitrile-nitrile and nitrile-alkyne coupling of Fc-C?N and FC-C?C-C?N.  

PubMed

The reactions of the Group?4 metallocene alkyne complexes, [Cp*2M(?2-Me3SiC2SiMe3)] (1?a: M=Ti, 1?b: M=Zr, Cp*=?5-pentamethylcyclopentadienyl), with the ferrocenyl nitriles, Fc-CN and Fc-C?C-C?N (Fc=Fe(?5-C5H5)(?5-C5H4)), is described. In case of Fc-C?N an unusual nitrile–nitrile C-C homocoupling was observed and 1-metalla-2,5-diaza-cyclopenta-2,4-dienes (3?a, b) were obtained. As the first step of the reaction with 1?b, the nitrile was coordinated to give [Cp*2Zr(?2-Me3SiC2SiMe3)(N?C-Fc)] (2?b). The reactions with the 3-ferrocenyl-2-propyne-nitrile FcC?C-C?N lead to an alkyne–nitrile C-C coupling of two substrates and the formation of 1-metalla-2-aza-cyclopenta-2,4-dienes (4?a, b). For M=Zr, the compound is stabilized by dimerization as evidenced by single-crystal X-ray structure analysis. The electrochemical behavior of 3?a, b and 4?a, b was investigated, showing decomposition after oxidation, leading to different redox-active products. PMID:24615841

Becker, Lisanne; Strehler, Frank; Korb, Marcus; Arndt, Perdita; Spannenberg, Anke; Baumann, Wolfgang; Lang, Heinrich; Rosenthal, Uwe

2014-03-10

390

Modular functionalized polyphosphines for supported materials: previously unobserved (31)P-NMR «through-space» ABCD spin systems and heterogeneous palladium-catalysed C-C and C-H arylation.  

PubMed

The modular design of polyphosphines, diversely functionalized for facile immobilization on virtually any kind of support, is reported. Previously unobserved ABCD (31)P NMR spin-spin systems evidence the control exercised on the polyphosphines conformation. We illustrate the catalytic performance at low Pd loading of the recyclable immobilized polyphosphines in C-C bond formation reactions. PMID:25008866

Beaupérin, Matthieu; Smaliy, Radomyr; Cattey, Hélène; Meunier, Philippe; Ou, Jun; Toy, Patrick H; Hierso, Jean-Cyrille

2014-07-24

391

Hydrogen bond coupling in sodium dihydrogen triacetate.  

PubMed

The coupling of hydrogen bonds is central to structures and functions of biological systems. Hydrogen bond coupling in sodium dihydrogen triacetate (SDHTA) is investigated as a model for the hydrogen bonded systems of the type O-H…O. The two-dimensional potential energy surface is derived from the full-dimensional one by selecting the relevant vibrational modes of the hydrogen bonds. The potential energy surfaces in terms of normal modes describing the anharmonic motion in the vicinity of the equilibrium geometry of SDHTA are calculated for the different species, namely, HH, HD, DH, and DD isotopomers. The ground state wave functions and their relation to the hydrogen bond structural parameters are discussed. It has been found that the hydrogen bonds in SDHTA are uncoupled, that is elongation of the deuterated hydrogen bond does not affect the non-deuterated one. PMID:25038632

Ahmed, Ashour A; Hilal, Rifaat H; Shibl, Mohamed F

2014-08-01

392

Research on Frictional Wear Properties of C\\/C Composite with Electric Current  

Microsoft Academic Search

\\u000a Using C\\/C composite and chrome bronze as a friction couple, the frictional wear properties of C\\/C composite with electric\\u000a current is studied in this paper. The results have shown that current, velocity and load are important factors to affect the\\u000a frictional wear properties of C\\/C composite with electric current. The coefficient of friction and the wear rate increase\\u000a with the

L. X. Jia; Y. Z. Zhang; J. Li; L. M. Sun; Y. W. Zhao

393

Dangling bond-induced graphitization process on the (111) surface of diamond nanoparticles.  

PubMed

The intrinsic mechanism of graphitization occurring on the (111) surface of nanodiamonds (NDs) during the transformation from NDs into bucky diamonds are explored using density functional theory (DFT) computations in conjunction with density functional based tight-binding simulations. The DFT results indicate that dangling bonds (DBs) on the ND surfaces play an important role in the graphitization process, and the orientation of the DBs on different ND surfaces determines whether there will be a graphitization process or not. Moreover, a criterion is proposed to estimate rupturing of the C-C bonds between different layers on the [111] direction in the NDs and is verified to be applicable to illustrate the phase transformation from sp(3) into sp(2) bonding structures. The energy contributions of the four-coordinated carbon atoms located at different positions on the (111) surface are exhibited for the first time and discussed in detail to gain a clear picture for the transition from NDs into bucky diamonds. The outcome may provide a deeper understanding on the influence of DBs upon the transformation from sp(3) into sp(2) bonding structures. PMID:21280789

Li, Le-sheng; Zhao, Xiang

2011-01-28

394

Excitation energies with linear response density matrix functional theory along the dissociation coordinate of an electron-pair bond in N-electron systems  

NASA Astrophysics Data System (ADS)

Time dependent density matrix functional theory in its adiabatic linear response formulation delivers exact excitation energies ?? and oscillator strengths f? for two-electron systems if extended to the so-called phase including natural orbital (PINO) theory. The Löwdin-Shull expression for the energy of two-electron systems in terms of the natural orbitals and their phases affords in this case an exact phase-including natural orbital functional (PILS), which is non-primitive (contains other than just J and K integrals). In this paper, the extension of the PILS functional to N-electron systems is investigated. With the example of an elementary primitive NO functional (BBC1) it is shown that current density matrix functional theory ground state functionals, which were designed to produce decent approximations to the total energy, fail to deliver a qualitatively correct structure of the (inverse) response function, due to essential deficiencies in the reconstruction of the two-body reduced density matrix (2RDM). We now deduce essential features of an N-electron functional from a wavefunction Ansatz: The extension of the two-electron Löwdin-Shull wavefunction to the N-electron case informs about the phase information. In this paper, applications of this extended Löwdin-Shull (ELS) functional are considered for the simplest case, ELS(1): one (dissociating) two-electron bond in the field of occupied (including core) orbitals. ELS(1) produces high quality ??(R) curves along the bond dissociation coordinate R for the molecules LiH, Li2, and BH with the two outer valence electrons correlated. All of these results indicate that response properties are much more sensitive to deficiencies in the reconstruction of the 2RDM than the ground state energy, since derivatives of the functional with respect to both the NOs and the occupation numbers need to be accurate.

van Meer, R.; Gritsenko, O. V.; Baerends, E. J.

2014-01-01

395

Excitation energies with linear response density matrix functional theory along the dissociation coordinate of an electron-pair bond in N-electron systems.  

PubMed

Time dependent density matrix functional theory in its adiabatic linear response formulation delivers exact excitation energies ?? and oscillator strengths f? for two-electron systems if extended to the so-called phase including natural orbital (PINO) theory. The Lo?wdin-Shull expression for the energy of two-electron systems in terms of the natural orbitals and their phases affords in this case an exact phase-including natural orbital functional (PILS), which is non-primitive (contains other than just J and K integrals). In this paper, the extension of the PILS functional to N-electron systems is investigated. With the example of an elementary primitive NO functional (BBC1) it is shown that current density matrix functional theory ground state functionals, which were designed to produce decent approximations to the total energy, fail to deliver a qualitatively correct structure of the (inverse) response function, due to essential deficiencies in the reconstruction of the two-body reduced density matrix (2RDM). We now deduce essential features of an N-electron functional from a wavefunction Ansatz: The extension of the two-electron Lo?wdin-Shull wavefunction to the N-electron case informs about the phase information. In this paper, applications of this extended Lo?wdin-Shull (ELS) functional are considered for the simplest case, ELS(1): one (dissociating) two-electron bond in the field of occupied (including core) orbitals. ELS(1) produces high quality ??(R) curves along the bond dissociation coordinate R for the molecules LiH, Li2, and BH with the two outer valence electrons correlated. All of these results indicate that response properties are much more sensitive to deficiencies in the reconstruction of the 2RDM than the ground state energy, since derivatives of the functional with respect to both the NOs and the occupation numbers need to be accurate. PMID:24437859

van Meer, R; Gritsenko, O V; Baerends, E J

2014-01-14

396

One-step synthesis of diazaspiro[4.5]decane scaffolds with exocyclic double bonds.  

PubMed

Unactivated yne-en-ynes reacted with a range of substituted aryl halides in the presence of Pd(OAc)2-PPh3 to afford diazaspiro[4.5]decane with exocyclic double bonds. Three carbon-carbon bonds are formed in this domino reaction, which involves highly regioselective C-C coupling and spiro scaffold steps. PMID:24956492

Li, Lidong; Hu, Qiong; Zhou, Pingping; Xie, Haifeng; Zhang, Xiaorong; Zhang, Hao; Hu, Yadong; Yin, Fei; Hu, Yimin

2014-07-01

397

On the different representations of the hole-correlation functions in the Hartree-Fock and the Hartree-Fock-Slater methods and their influence on bond energy calculations  

Microsoft Academic Search

We have investigated the change in shape of the Hartree–Fock Fermi-hole correlation function upon bond formation. Our analysis indicates that the molecular Fermi-hole correlation function is on the whole considerably more diffuse than its atomic counterpart. It is shown that this imbalance gives rise to HF bond energies which in many instances are much smaller than the experimental values. The

Vincenzo Tschinke; Tom Ziegler

1990-01-01

398

29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.  

Code of Federal Regulations, 2010 CFR

...bonds, separate bonds and additional bonding. 2580.412-20 Section 2580...DEPARTMENT OF LABOR TEMPORARY BONDING RULES UNDER THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES General Bond Rules §...

2009-07-01

399

29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.  

Code of Federal Regulations, 2010 CFR

...bonds, separate bonds and additional bonding. 2580.412-20 Section 2580...DEPARTMENT OF LABOR TEMPORARY BONDING RULES UNDER THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES General Bond Rules §...

2010-07-01

400

Overview of C/C-SiC Composite Development for the Orion Launch Abort System  

NASA Technical Reports Server (NTRS)

Past and present efforts by the authors to further understanding of the ceramic matrix composite (CMC) material used in the valve components of the Orion Launch Abort System (LAS) Attitude Control Motor (ACM) will be presented. The LAS is designed to quickly lift the Orion Crew Exploration Vehicle (CEV) away from its launch vehicle in emergency abort scenarios. The ACM is a solid rocket motor which utilizes eight throttleable nozzles to maintain proper orientation of the CEV during abort operations. Launch abort systems have not been available for use by NASA on manned launches since the last Apollo ]Saturn launch in 1975. The CMC material, carbon-carbon/silicon-carbide (C/C-SiC), is manufactured by Fiber Materials, Inc. and consists of a rigid 4-directional carbon-fiber tow weave reinforced with a mixed carbon plus SiC matrix. Several valve and full system (8-valve) static motor tests have been conducted by the motor vendor. The culmination of these tests was the successful flight test of the Orion LAS Pad Abort One (PA ]1) vehicle on May 6, 2010. Due to the fast pace of the LAS development program, NASA Marshall Space Flight Center assisted the LAS community by performing a series of material and component evaluations using fired hardware from valve and full ]system development motor tests, and from the PA-1 flight ACM motor. Information will be presented on the structure of the C/C-SiC material, as well as the efficacy of various non ]destructive evaluation (NDE) techniques, including but not limited to: radiography, computed tomography, nanofocus computed tomography, and X-ray transmission microscopy. Examinations of the microstructure of the material via scanning electron microscopy and energy dispersive spectroscopy will also be discussed. The findings resulting from the subject effort are assisting the LAS Project in risk assessments and in possible modifications to the final ACM operational design.

Allen, Lee R.; Valentine, Peter G.; Schofield, Elizabeth S.; Beshears, Ronald D.; Coston, James E.

2012-01-01

401

Guided ion beam studies of the reactions of Cr{sub n}{sup +} (n=1{endash}18) with CO{sub 2}: Chromium cluster oxide bond energies  

SciTech Connect

The kinetic energy dependence of the reactions of Cr{sub n}{sup +} (n=1{endash}18) with CO{sub 2} are studied in a guided ion beam mass spectrometer. The primary product ions are Cr{sub n}O{sup +}, which then decompose by sequential loss of chromium atoms as the kinetic energy is increased. Simple collision-induced dissociation to form the Cr{sub n{minus}1}{sup +} product ions is also observed. Large cluster ions, n{ge}9, form the Cr{sub n}CO{sub 2}{sup +} adduct at low kinetic energies. For many cluster sizes, the cross section for the primary reaction, Cr{sub n}{sup +}+CO{sub 2}{r_arrow}Cr{sub n}O{sup +}+CO, exhibits an interesting bimodal energy behavior that is discussed in some detail. Cr{sub n}{sup +}{endash}O bond energies are measured and found to compare well with measurements obtained from guided ion beam studies of the Cr{sub n}{sup +}+O{sub 2} systems. The trends in this thermochemistry are discussed and compared to bulk phase oxidation values. {copyright} {ital 1998 American Institute of Physics.}

Griffin, J.B.; Armentrout, P.B. [Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States)] [Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States)

1998-05-01

402

Sequential bond energies and barrier heights for the water loss and charge separation dissociation pathways of Cd(2+)(H2O)n, n = 3-11.  

PubMed

The bond dissociation energies for losing one water from Cd(2+)(H(2)O)(n) complexes, n = 3-11, are measured using threshold collision-induced dissociation in a guided ion beam tandem mass spectrometer coupled with a thermal electrospray ionization source. Kinetic energy dependent cross sections are obtained for n = 4-11 complexes and analyzed to yield 0 K threshold measurements for loss of one, two, and three water ligands after accounting for multiple collisions, kinetic shifts, and energy distributions. The threshold measurements are converted from 0 to 298 K values to give the hydration enthalpies and free energies for sequentially losing one water from each complex. Theoretical geometry optimizations and single point energy calculations are performed on reactant and product complexes using several levels of theory and basis sets to obtain thermochemistry for comparison to experiment. The charge separation process, Cd(2+)(H(2)O)(n) ? CdOH(+)(H(2)O)(m) + H(+)(H(2)O)(n-m-1), is also observed for n = 4 and 5 and the competition between this process and water loss is analyzed. Rate-limiting transition states for the charge separation process at n = 3-6 are calculated and compared to experimental threshold measurements resulting in the conclusion that the critical size for this dissociation pathway of hydrated cadmium is n(crit) = 4. PMID:21428620

Cooper, Theresa E; Armentrout, P B

2011-03-21

403

Reinterpretation of the vibrational spectroscopy of the medicinal bioinorganic synthon c,c,t-[Pt(NH3) 2Cl 2(OH) 2].  

PubMed

The Pt(IV) complex c,c,t-[Pt(NH3)2Cl2(OH)2] is an important intermediate in the synthesis of Pt(IV) anticancer prodrugs and has been investigated as an anticancer agent in its own right. An analysis of the vibrational spectroscopy of this molecule was previously reported (Faggiani et al., Can. J. Chem. 60:529, 1982), in which crystallographic determination of the structure of the complex permitted a site group approach. The space group, however, was incorrectly assigned. In the present study we have redetermined at high resolution crystal structures of c,c,t-[Pt(NH3)2Cl2(OH)2] and c,c,t-[Pt(NH3)2Cl2(OH)2]·H2O2, which makes possible discussion of the effect of hydrogen bonding on the N-H and O-H vibrational bands. The correct crystallographic site symmetry of the platinum complex in the c,c,t-[Pt(NH3)2Cl2(OH)2] structure is used to conduct a new vibrational analysis using both group-theoretical and modern density functional theory methods. This analysis reveals the nature and symmetry of the "missing band" described in the original publication and suggests a possible explanation for its disappearance. PMID:24515615

Johnstone, Timothy C; Lippard, Stephen J

2014-06-01

404

Strength, ultrasonic and metallurgical evaluation of diffusion bonds  

SciTech Connect

Diffusion bonding allows similar and dissimilar materials to be bonded together in near net shape. However, differentiation of almost perfect diffusion bonds, with little variation in their acoustic response, is of critical importance since relatively significant changes in bond strength may be a consequence. Challenge is to find ultrasonic techniques sensitive enough to detect small imperfections at interface. Diffusion bonds have been produced that show only a slight variation in a single frequency reflection measurement. The total energy, reflected from bond line, can differentiate these diffusion bonds. This evaluation is based on Parseval`s theorem which states that energy in time domain is proportional to energy in the frequency domain. This measurement takes advantage of presence of voids in the diffusion bonds as well as of the interdiffusion zone. Cu and Ni were chosen as the materials to be bonded due to the case of microstructural control. Diffusion bonds fabricated of Ti-6Al-4V are also discussed.

Ojard, G.C.; Buck, O.; Rehbein, D.K.

1993-10-01

405

Role of acid-base interfacial bonding in adhesion  

Microsoft Academic Search

The strength of macroscopic adhesive bonds of polymers is known to be directly proportional to the microscopic exothermic interfacial energy changes of bond formation, as measured by Dupre's 'work of adhesion'. Since the work of adhesion can be very appreciably increased by interfacial acid-base bonding with concomitant increases in adhesive bond strength, it is important to understand the acid-base character

Frederick M. Fowkes

1987-01-01

406

The impact of carbon-hydrogen bond dissociation energies on the prediction of the cytochrome P450 mediated major metabolic site of drug-like compounds.  

PubMed

Cytochrome P450 is a family of enzymes which is estimated to be responsible for over 75% of phase I drug metabolism. In this process carbon hydrogen bonds (C-H) are broken for hydroxylation indicating that the bond dissociation energy (BDE) plays a pivotal role. A host of experimentally derived C-H BDEs were benchmarked against their theoretical counterparts and an excellent correlation was found (R(2) = 0.9746, n = 100). The C-H BDEs were calculated for fifty drugs with known major hydrogen abstraction sites. Of those twelve (24%) had their major metabolic site at the lowest C-H BDE. The most prominent factor in determining the metabolic site is the presence of tertiary and secondary amine moieties (44%). Other features such as lipophilicity and steric accessibility of the pertinent molecular scaffolds are also important. Nevertheless, out of the 586 C-H BDEs calculated the average of the major hydrogen abstraction sites are statistically significantly lower by 6.9-12.8 kcal/mol (p-value = 7.257 × 10(-9)). This means that C-H BDEs are an indispensable component in building reliable models of first pass metabolism of xenobiotics. PMID:22960693

Drew, Kurt L M; Reynisson, Jóhannes

2012-10-01

407

Bond strengths of two dental bonding systems.  

PubMed

A new bonding system named Kevloc has been introduced. It is based on acrylization of the metal surface with the goal of preventing the occurrence of a marginal gap between the metal and the resin. The purpose of this investigation was to determine the values of the shear bond strength achieved using the Kevloc technique on Ag-Pd (Auropal SE) and Co-Cr (Basil S) alloys and to compare them with those obtained with the OVS technique. The shear bond strengths were measured with the Smitz-Schulmayer shear test in a universal testing machine for polymer materials. A microscope image analyzer was used to measure the thickness of bonding layers and to reveal the possible occurrence of the marginal gap with both techniques. No marginal gap was detected with either technique. Kevloc provided better results than OVS only in a group of specimens tested after polymerization. Immersion in water and thermocycling reduced the initially high bond strength values of Kevloc specimens, whereas the bond strength values of OVS specimens remained unchanged regardless of which aging treatment was used. Microscopic examination did not reveal the existence of the marginal gap for either bonding system. According to the results obtained, it can be concluded that the Kevloc bonding system does not provide better shearing bond strength than the OVS bonding system. PMID:10920659

Vojvodic, D; Jerolimov, V; Zabarovic, D; Loncar, A

2000-07-01

408

Influence of crystallography upon critical nucleus shapes and kinetics of homogeneous f. c. c. -f. c. c. nucleation-V. The origin of GP zones in Al-Ag and Al-Cu alloys  

SciTech Connect

GP zone formation in aluminum-base alloys has been proposed, by previous investigators, to take place by spinodal decomposition or by homogeneous nucleation and growth. The possibilities of these two mechanisms are examined here for two alloy systems, Al-Ag and Al-Cu, representing two extreme cases, a narrow and a (potentially) very wide miscibility gap, respectively, resulting in low and high interphase boundary energies. The coherent spinodal and the temperature-composition curve corresponding to abundant homogeneous f.c.c.-f.c.c. nucleation were calculated for both systems. In Al-Ag alloys, the nucleation barrier is so low that negligible undercooling is needed to achieve abundant nucleation. Hence cooling into the spinodal region with ordinary quenching rates is virtually impossible. In Al-Cu, however, the inverse situation is present and GP zone formation by (or aided by) spinodal decomposition should be feasible if the diffusivity remains sufficiently high in the spinodal region. Detailed evaluation of the latter proposal is prevented, however, by the incompleteness of thermodynamic information on f.c.c. Al-Cu alloys.

Le Goues, F.K.; Aaronson, H.I.; Lee, Y.W.; Wright, R.N.

1984-10-01

409

Testing of DLR C/C-SiC for HIFiRE 8 Scramjet Combustor  

NASA Technical Reports Server (NTRS)

Ceramic Matrix Composites (CMCs) have been proposed for hot structures in scramjet combustors. Previous studies have calculated significant weight savings by utilizing CMCs (active and passive) versus actively cooled metallic scramjet structures. Both a C/C and a C/C-SiC material system fabricated by DLR (Stuttgart, Germany) are being considered for use in a passively cooled combustor design for HIFiRE 8, a joint Australia / AFRL hypersonic flight program, expected to fly at Mach 7 for approximately 30 sec, at a dynamic pressure of 55 kPa. Flat panels of the DLR C/C and the C/C-SiC were tested in the NASA Langley Direct Connect Rig (DCR) at Mach 5 and Mach 6 enthalpy for several minutes. Gaseous hydrogen fuel was used to fuel the scramjet combustor. The test panels were instrumented with embedded Type K and Type S thermocouples. Zirconia felt insulation was used in some of the tests to increase the surface temperature of the C/C-SiC panel for approximately 350degF. The final C/C-SiC panel was tested for 3 cycles totaling over 135 sec at Mach 6 enthalpy. Slightly more erosion was observed on the C/C panel than the C/C-SiC panels, but both material systems demonstrated acceptable recession performance for the HIFiRE 8 flight.

Glass, David E.; Capriotti, Diego P.; Reimer, Thomas; Kutemeyer, Marius; Smart, Michael

2013-01-01

410

Evidence for intramolecular OH?? hydrogen bonding in unsaturated alcohols from UV photoelectron spectroscopy  

NASA Astrophysics Data System (ADS)

The gas phase He(I) photoelectron (PE) spectra of several unsaturated alcohols ( 1- 11) have been measured and analysed with respect to intramolecular OH⋯? hydrogen bonding. Evidence for such a hydrogen bond has been detected in the spectra of 2-allylphenol ( 1) and 2-phenylethan-1-ol ( 3). 1 exists as a conformational mixture of a hydrogen bonded form 1a and an open form 1b in a composition of roughly 2:1. A strong ionization band (IP v=10.01 eV; where IP v is the vertical ionization potential) is assigned to the ethylenic C?C double bond in the major conformer ( 1a) and a weak band (IP v=9.72 eV) to that of the minor conformer ( 1b). The latter IP coincides with the corresponding ionization of allylbenzene. In the series of ?-phenylalkan-1-ols, compound 3 exhibits an unusually low n?(O) ionization indicating hydrogen bonding between the OH group and the ? electron system of the phenyl ring. The higher homologs 4 and 5 prefer 'open' conformations without such interaction. The PE spectra of alkenols such as but-3-en-1-ol ( 7) and pent-4-en-1-ol ( 8) as well as of alkynols such as but-3-yn-1-ol ( 10) and pent-4-yn-1-ol ( 11) are consistent with OH⋯? hydrogen bonded conformers. The methanol/ethylene hetero-dimer has a T-shaped structure, as indicated by B3LYP/6-311++G(d) calculations, with a binding energy of 5.65 kJ mol -1.

Kowski, Klaus; Lüttke, Wolfgang; Rademacher, Paul

2001-06-01

411

The covered bond market  

Microsoft Academic Search

The covered bond market offers investors an alternative to developed country government securities. The valuation of covered bonds is complex. While there is some evidence of differences in the pricing of these bonds by nationality of issuer, these appear to be only weakly related to differences in the respective legislative frameworks. Recent cases show the pricing of covered bonds to

Frank Packer; Ryan Stever; Christian Upper

2007-01-01

412

Wire Bond Temperature Sensor  

Microsoft Academic Search

This work reports the first demonstration of a bond pad test structure with embedded thermopile sensors for the measurement of the transient temperature response during the wire bonding operation. This paper will present the design and operation of the bond pad test structure and show and discuss temperature measurements during the wire bonding operation. The test structure can be used

Shivesh Suman; Michael Gaitan; Yogendra Joshi; George Harman

413

Rh-catalyzed oxidative C-C bond formation and C-N bond cleavage: direct access to C2-olefinated free (NH)-indoles and pyrroles.  

PubMed

The rhodium-catalyzed oxidative C2-olefination of indoles and pyrroles containing N-arylcarboxamide directing groups with a range of alkenes and subsequent cleavage of directing groups is described. This method provides direct and efficient access to C2-functionalized free (NH)-heterocycles. PMID:24480981

Sharma, Satyasheel; Han, Sangil; Kim, Mirim; Mishra, Neeraj Kumar; Park, Jihye; Shin, Youngmi; Ha, Jimin; Kwak, Jong Hwan; Jung, Young Hoon; Kim, In Su

2014-03-21

414

Cation-ether complexes in the gas phase: Bond dissociation energies and equilibrium structures of Li{sup +}[O(CH{sub 3}){sub 2}]{sub x}, x=1-4  

SciTech Connect

Bond dissociation energies, equilibrium structures, and harmonic vibrational frequencies of Li{sup +}[O(CH{sub 3}){sub 2}]{sub x}, x=1-4, are reported. The bond dissociation energies are determined experimentally by analysis of the thresholds for collision-induced dissociation of the cation-ether complexes by xenon (measured using guided ion beam mass spectrometry) and computationally by ab initio electronic structure calculation at the RHF and MP2 levels of theory. In all cases, the primary and lowest energy dissociation channel observed experimentally is endothermic loss of one ether molecule. The cross-section thresholds are interpreted to yield 0 and 298 K bond energies after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and unimolecular decay rates. The experimental and theoretical bond energies are in good agreement with previous experimental results. Some of the discrepancies disappear at the complete basis set limit. The equilibrium structures are determined primarily by strong electrostatic and polarization interactions. Charge transfer interactions are also important, as indicated by natural energy decomposition analysis of the calculated wave functions. 59 refs., 6 figs., 5 tabs.

More, M.B.; Armentrout, P.B. [Univ. of Utah, Salt Lake City, UT (United States)] [Univ. of Utah, Salt Lake City, UT (United States); Glendening, E.D.; Ray, D.; Feller, D. [Pacific Northwest Lab., Richland, WA (United States)] [Pacific Northwest Lab., Richland, WA (United States)

1996-02-01

415

Halogen Bonding versus Hydrogen Bonding: A Molecular Orbital Perspective.  

PubMed

We have carried out extensive computational analyses of the structure and bonding mechanism in trihalides DX???A(-) and the analogous hydrogen-bonded complexes DH???A(-) (D, X, A=F, Cl, Br, I) using relativistic density functional theory (DFT) at zeroth-order regular approximation ZORA-BP86/TZ2P. One purpose was to obtain a set of consistent data from which reliable trends in structure and stability can be inferred over a large range of systems. The main objective was to achieve a detailed understanding of the nature of halogen bonds, how they resemble, and also how they differ from, the better understood hydrogen bonds. Thus, we present an accurate physical model of the halogen bond based on quantitative Kohn-Sham molecular orbital (MO) theory, energy decomposition analyses (EDA) and Voronoi deformation density (VDD) analyses of the charge distribution. It appears that the halogen bond in DX???A(-) arises not only from classical electrostatic attraction but also receives substantial stabilization from HOMO-LUMO interactions between the lone pair of A(-) and the ?* orbital of D-X. PMID:24551497

Wolters, Lando P; Bickelhaupt, F Matthias

2012-04-01

416

Halogen Bonding versus Hydrogen Bonding: A Molecular Orbital Perspective  

PubMed Central

We have carried out extensive computational analyses of the structure and bonding mechanism in trihalides DX???A? and the analogous hydrogen-bonded complexes DH???A? (D, X, A=F, Cl, Br, I) using relativistic density functional theory (DFT) at zeroth-order regular approximation ZORA-BP86/TZ2P. One purpose was to obtain a set of consistent data from which reliable trends in structure and stability can be inferred over a large range of systems. The main objective was to achieve a detailed understanding of the nature of halogen bonds, how they resemble, and also how they differ from, the better understood hydrogen bonds. Thus, we present an accurate physical model of the halogen bond based on quantitative Kohn–Sham molecular orbital (MO) theory, energy decomposition analyses (EDA) and Voronoi deformation density (VDD) analyses of the charge distribution. It appears that the halogen bond in DX???A? arises not only from classical electrostatic attraction but also receives substantial stabilization from HOMO–LUMO interactions between the lone pair of A? and the ?* orbital of D–X.

Wolters, Lando P; Bickelhaupt, F Matthias

2012-01-01

417

H-H, C-H, and C-C NMR spin-spin coupling constants calculated by the FP-INDO method for aromatic hydrocarbons  

NASA Technical Reports Server (NTRS)

The FP-INDO (finite perturbation-intermediate neglect of differential overlap) method is used to calculate the H-H, C-H, and C-C coupling constants in hertz for molecules of six different benzenoid hydrocarbons: benzene, naphthalene, biphenyl, anthracene, phenanthrene, and pyrene. The calculations are based on both the actual and the average molecular geometries. It is found that only the actual molecular geometries can always yield the correct relative order of values for the H-H coupling constants. For the calculated C-C coupling constants, as for the calculated C-H coupling constants, the signs are positive (negative) for an odd (even) number of bonds connecting the two nuclei. Agreements between the calculated and experimental values of the coupling constants for all six molecules are comparable to those reported previously for other molecules.

Long, S. A. T.; Memory, J. D.

1978-01-01