Sample records for cycloalkenes
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NASA Astrophysics Data System (ADS)
Zhou, Chen-Chen; Ke, Xiao-Na; Xu, Xiu-Fang
2015-07-01
The (5+2) cycloaddition reaction utilising cycloalkenes is rare, although it is one of the most efficient methods of constructing seven-membered fused rings because of its high atom- and step-economy. In this study, we used quantum mechanical calculations to predict the plausibility of using the Rh-catalysed intermolecular (5+2) cycloaddition of 3-acyloxy-1,4-enynes and cycloalkenes to produce fused seven-membered carbocycles. The calculation results suggest a convenient, highly efficient and energetically practical approach. Strained cycloalkenes, such as cyclopropene, have been predicted to be active, and the desired bicyclic product should be favoured, accompanied by the formation of byproducts from rearrangement reactions. The energy barriers of the alkene insertion step were analysed by the distortion/interaction model to disclose the origins of the different reactivities of cycloalkenes with different ring sizes.
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Hussain, Nazar; Tatina, Madhu Babu; Rasool, Faheem; Mukherjee, Debaraj
2016-10-25
Sugar enol ethers undergo efficient coupling at C-2 with unactivated cycloalkenes under a low Pd loading affording allylic substitution products. High diastereoselectivity was observed at the allylic centre with sterically hindered substrates. Generation of a π-allyl complex by the Pd(ii) catalyst via cleavage of the allylic C-H bond of the cycloalkene may be responsible for the formation of sp 2 -sp 3 coupling products.
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Cis and Trans Isomers of Cycloalkenes
ERIC Educational Resources Information Center
Barrows, Susan E.; Eberlein, Thomas H.
2005-01-01
A study investigates the strain in medium-sized cycloalkenes and the geometric and electronic distortions through which alkenes can relieve that strain. Literature data is summarized and results are presented with the aim of providing a concise reference for those interested in addressing the topic in an introductory organic chemistry curriculum.
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The Pauson-Khand reaction of medium sized trans-cycloalkenes.
Lledó, Agustí; Fuster, Aida; Revés, Marc; Verdaguer, Xavier; Riera, Antoni
2013-04-14
Medium sized trans-cycloalkenes are unusually reactive in the intermolecular Pauson-Khand reaction (PKR) with regard to typical monocyclic alkenes. This is due to the ring strain imparted by the E stereochemistry. The PKR of these alkenes offers a modular, regioselective and straightforward entry to trans fused [n.3.0] bicyclic scaffolds (n = 6-8).
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IMPROVED METHOD FOR THE STORAGE OF GROUND WATER SAMPLES CONTAINING VOLATILE ORGANIC ANALYTES
The sorption of volatile organic analytes from water samples by the Teflon septum surface used with standard glass 40-ml sample collection vials was investigated. Analytes tested included alkanes, isoalkanes, olefins, cycloalkanes, a cycloalkene, monoaromatics, a polynuclear arom...
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FORMATION OF THE OH RADICAL IN THE REACTION OF OZONE WITH SEVERAL CYCLO-ALKENES. (R826236)
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...
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Understanding Rotation about a C=C Double Bond
ERIC Educational Resources Information Center
Barrows, Susan E.; Eberlein, Thomas H.
2005-01-01
The study focuses on the process and energetic cost of twisting around a C=C double bond and provides instructors with a simple vehicle for rectifying the common misrepresentation of C=C double bonds as rigid and inflexible. Discussions of cis and trans isomers of cycloalkenes are a good entry point for introducing students to the idea of a…
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ERIC Educational Resources Information Center
Barrows, Susan E.; Eberlein, Thomas H.
2004-01-01
Activities in which students explore the fundamental reasons behind the unusual instability of the trans isomers in medium-sized cycloalkenes by using the results of molecular modeling are described. Exercises have been proposed to explore the structures of cycloheptene and cyclooctene by Hehre and others which would be helpful to disabuse…
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Berndt, Torsten; Richters, Stefanie; Kaethner, Ralf; Voigtländer, Jens; Stratmann, Frank; Sipilä, Mikko; Kulmala, Markku; Herrmann, Hartmut
2015-10-15
The gas-phase reaction of ozone with C5-C8 cycloalkenes has been investigated in a free-jet flow system at atmospheric pressure and a temperature of 297 ± 1 K. Highly oxidized RO2 radicals bearing at least 5 O atoms in the molecule and their subsequent reaction products were detected in most cases by means of nitrate-CI-APi-TOF mass spectrometry. Starting from a Criegee intermediate after splitting-off an OH-radical, the formation of these RO2 radicals can be explained via an autoxidation mechanism, meaning RO2 isomerization (ROO → QOOH) and subsequently O2 addition (QOOH + O2 → R'OO). Time-dependent RO2 radical measurements concerning the ozonolysis of cyclohexene indicate rate coefficients of the intramolecular H-shifts, ROO → QOOH, higher than 1 s(-1). The total molar yield of highly oxidized products (predominantly RO2 radicals) from C5-C8 cycloalkenes in air is 4.8-6.0% affected with a calibration uncertainty by a factor of about two. For the most abundant RO2 radical from cyclohexene ozonolysis, O,O-C6H7(OOH)2O2 ("O,O" stands for two O atoms arising from the ozone attack), the determination of the rate coefficients of the reaction with NO2, NO, and SO2 yielded (1.6 ± 0.5) × 10(-12), (3.4 ± 0.9) × 10(-11), and <10(-14) cm(3) molecule(-1) s(-1), respectively. The reaction of highly oxidized RO2 radicals with other peroxy radicals (R'O2) leads to detectable accretion products, RO2 + R'O2 → ROOR' + O2, which allows to acquire information on peroxy radicals not directly measurable with the nitrate ionization technique applied here. Additional experiments using acetate as the charger ion confirm conclusively the existence of highly oxidized RO2 radicals and closed-shell products. Other reaction products, detectable with this ionization technique, give a deeper insight in the reaction mechanism of cyclohexene ozonolysis.
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Mechanism of di-tert-butylsilylene transfer from a silacyclopropane to an alkene.
Driver, Tom G; Woerpel, K A
2003-09-03
Kinetic and thermodynamic studies of the reactions of cyclohexene silacyclopropane 1 and monosubstituted alkenes suggested a possible mechanism for di-tert-butylsilylene transfer. The kinetic order in cyclohexene silacyclopropane 1 and cyclohexene were determined to be 1 and -1, respectively. Saturation kinetic behavior in monosubstituted alkene concentration was observed. Competition experiments between substituted styrenes and a deficient amount of di-tert-butylsilylene from 1 correlated well with the Hammett equation and provided a rho value of -0.666 +/- 0.008, using sigma(p) constants. These data supported a two-step mechanism involving reversible di-tert-butylsilylene extrusion from 1, followed by irreversible concerted electrophilic attack of the silylene on the monosubstituted alkene. Eyring activation parameters were found to be DeltaH++ = 22.1 +/- 0.9 kcal.mol(-1) and DeltaS++ = -15 +/- 2 eu. Competition experiments between cycloalkenes and allylbenzene determined cycloalkenes to be more efficient silylene traps (k(rel) =1.3, DeltaDeltaG++ = 0.200 kcal.mol(-1)). A summary of the data resulted in a postulated reaction coordinate diagram. The mechanistic studies enabled rational modification of reaction conditions that improved the synthetic utility of silylene transfer. Removal of the volatile cyclohexene from the reaction mixture into an evacuated headspace led to the formation of previously inaccessible cyclohexene-derived silacyclopropanes.
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Synthesis of the 1-Monoester of 2-Ketoalkanedioic Acids, e.g., Octyl α-Ketoglutarate
Jung, Michael E.; Deng, Gang
2012-01-01
Oxidative cleavage of cycloalkene-1-carboxylates, made from the corresponding carboxylic acids, and subsequent oxidation of the resulting ketoaldehyde afforded the important 1-monoesters of 2-ketoalkanedioic acids. Thus ozonolysis of octyl cyclobutene-1-carboxylate followed by sodium chlorite oxidation afforded the 1-monooctyl 2-ketoglutarate. This is a cell-permeable prodrug form of α-ketoglutarate, an important intermediate in the tricarboxylic acid (TCA, Krebs) cycle and a promising therapeutic agent in its own right. PMID:23163977
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A new approach to promoting sluggish Diels-Alder reactions: dihapto-coordination of the diene.
Liu, Weijun; You, Fei; Mocella, Christopher J; Harman, W Dean
2006-02-08
The cycloaddition between 1,3-cyclohexadiene and various enones and enals (methyl vinyl ketone, ethyl vinyl ketone, methacrolien) is accomplished at room temperature in yields ranging from 51 to 68% without the use of Lewis acids, high pressures, or microwave reactors. This normally sluggish cyclization is accomplished by precoordination of the diene to a pi-basic molybdenum complex. The eta2-bound metal is thought to promote a Michael reaction between the uncoordinated portion of the diene and the enone, and the resulting enolate then closes to form the cycloalkene product. The organic cycloadduct is removed by oxidation with air or with silver triflate in nearly quantitative yield. For more sterically hindered enones (e.g., mesityl oxide) and for methyl acrylate, the desired outcome requires the use of BF3.OEt2, and yields are significantly lower (15-35%)
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Stoyanov, Evgenii S.; Stoyanova, Irina V.; Reed, Christopher A.
2009-01-01
The competitive substitution of the anion in contact ion pairs of the type [Oct3NH+]B(C6F5)4− by unsaturated hydrocarbons L in accordance with the equilibrium Oct3NH+⋯Anion− + nL ↔ [Oct3NH+⋯Ln]Anion− has been studied in CCl4 solution. On the basis of equilibrium constants K and shifts of νNH to low frequency, it is established that complexed Oct3NH+⋯Ln cations with n = 1 and 2 are formed, having unidentate and bifurcated N–H+⋯π hydrogen bonds, respectively. Bifurcated H-bonds to unsaturated hydrocarbons have not been observed previously. The unsaturated hydro-carbons studied include benzene and methylbenzenes, fused-ring aromatics, alkenes, conjugated dienes, and alkynes. From the magnitude of the red shifts in N-H stretching frequencies, ΔνNH, a new scale for ranking the π-basicity of unsaturated hydrocarbons is proposed: fused-ring aromatics ≤ benzene < toluene < xylene < mesitylene < durene < conjugated dienes ∼ 1-alkynes < pentamethylbenzene < hexamethyl-benzene < internal alkynes ∼ cyclo-alkenes < 1-methylcycloalkenes. This scale is relevant to the discussion of π complexes for incipient protonation reactions and to understanding N–H+⋯π hydrogen bonding in proteins and molecular crystals. PMID:18637650
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Phase separation of bio-oil produced by co-pyrolysis of corn cobs and polypropylene
NASA Astrophysics Data System (ADS)
Supramono, D.; Julianto; Haqqyana; Setiadi, H.; Nasikin, M.
2017-11-01
In co-pyrolysis of biomass-plastics, bio-oil produced contains both oxygenated and non-oxygenated compounds. High oxygen composition is responsible for instability and low heating value of bio-oil and high acid content for corrosiveness. Aims of the present work are to evaluate possibilities of achieving phase separation between oxygenated and non-oxygenated compounds in bio-oil using a proposed stirred tank reactor and to achieve synergistic effects on bio-oil yield and non-oxygenated compound layer yield. Separation of bio-oil into two layers, i.e. that containing oxygenated compounds (polar phase) and non-oxygenated compounds (non-polar phase) is important to obtain pure non-polar phase ready for the next processing of hydrogenation and used directly as bio-fuel. There has been no research work on co-pyrolysis of biomass-plastic considering possibility of phase separation of bio-oil. The present work is proposing a stirred tank reactor for co-pyrolysis with nitrogen injection, which is capable of tailoring co-pyrolysis conditions leading to low viscosity and viscosity asymmetry, which induce phase separation between polar phase and non-polar phase. The proposed reactor is capable of generating synergistic effect on bio-oil and non-polar yields as the composition of PP in feed is more than 25% weight in which non-polar layers contain only alkanes, alkenes, cycloalkanes and cycloalkenes.
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Li, Xuehua; Zhao, Wenxing; Li, Jing; Jiang, Jingqiu; Chen, Jianji; Chen, Jingwen
2013-08-01
To assess the persistence and fate of volatile organic compounds in the troposphere, the rate constants for the reaction with ozone (kO3) are needed. As kO3 values are only available for hundreds of compounds, and experimental determination of kO3 is costly and time-consuming, it is of importance to develop predictive models on kO3. In this study, a total of 379 logkO3 values at different temperatures were used to develop and validate a model for the prediction of kO3, based on quantum chemical descriptors, Dragon descriptors and structural fragments. Molecular descriptors were screened by stepwise multiple linear regression, and the model was constructed by partial least-squares regression. The cross validation coefficient QCUM(2) of the model is 0.836, and the external validation coefficient Qext(2) is 0.811, indicating that the model has high robustness and good predictive performance. The most significant descriptor explaining logkO3 is the BELm2 descriptor with connectivity information weighted atomic masses. kO3 increases with increasing BELm2, and decreases with increasing ionization potential. The applicability domain of the proposed model was visualized by the Williams plot. The developed model can be used to predict kO3 at different temperatures for a wide range of organic chemicals, including alkenes, cycloalkenes, haloalkenes, alkynes, oxygen-containing compounds, nitrogen-containing compounds (except primary amines) and aromatic compounds. Copyright © 2013 Elsevier Ltd. All rights reserved.
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Park, Hyeon; Kang, Eun-Hye; Müller, Laura; Choi, Tae-Lim
2016-02-24
Tandem ring-opening/ring-closing metathesis (RO/RCM) results in extremely fast living polymerization; however, according to previous reports, only monomers containing certain combinations of cycloalkenes, terminal alkynes, and nitrogen linkers successfully underwent tandem polymerization. After examining the polymerization pathways, we proposed that the relatively slow intramolecular cyclization might lead to competing side reactions such as intermolecular cross metathesis reactions to form inactive propagating species. Thus, we developed two strategies to enhance tandem polymerization efficiency. First, we modified monomer structures to accelerate tandem RO/RCM cyclization by enhancing the Thorpe-Ingold effect. This strategy increased the polymerization rate and suppressed the chain transfer reaction to achieve controlled polymerization, even for challenging syntheses of dendronized polymers. Alternatively, reducing the reaction concentration facilitated tandem polymerization, suggesting that the slow tandem RO/RCM cyclization step was the main reason for the previous failure. To broaden the monomer scope, we used monomers containing internal alkynes and observed that two different polymer units with different ring sizes were produced as a result of nonselective α-addition and β-addition on the internal alkynes. Thorough experiments with various monomers with internal alkynes suggested that steric and electronic effects of the alkyne substituents influenced alkyne addition selectivity and the polymerization reactivity. Further polymerization kinetics studies revealed that the rate-determining step of monomers containing certain internal alkynes was the six-membered cyclization step via β-addition, whereas that for other monomers was the conventional intermolecular propagation step, as observed in other chain-growth polymerizations. This conclusion agrees well with all those polymerization results and thus validates our strategies.
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Thermo-analytical and physico-chemical characterisation of organoclays and polymer-clay nacomposites
NASA Astrophysics Data System (ADS)
Cunningham, Andrew
A variety of modified clay minerals have been screened to determine their effectiveness as agents for the production of polystyrene-clay nanocomposites. The n-alkylammonium and n-alkyltrimethylammonium surfactants employed to compatibilise the aluminosilicate layers of the minerals were shown to degrade through a series of stages and mechanisms to yield a hydrocarbon product mixture consisting of a homologous series of saturated and unsaturated hydrocarbons, also, the dehydrocyclisation (DHC) of fragmented alkyl chains was shown to lead to the production of various ring compounds which included substituted cycloalkenes, benzene and toluene.The thermal stability of various cation exchanged modification treatments have been analysed. These organoclays have been characterised by XRD, TGA and TG-MS. The evolved gas analysis conducted by TG-MS was employed to identify which products were being thermally desorbed under thermal events previously seen when using TGA. In particular attention was paid to the activity of these materials with respect to the formation of linear, branched and cyclic aliphatics and aromatics from the feedstock surfactants.Intra-series comparisons of different organoclays showed that as the alkyl chain length of the n-alkylammonium surfactants was increased the concentration of thermal desorption products at approximately 400 °C was also increased. However, characterisation of n-alkyltrimethylammonium exchanged MMT showed that the concentration of thermal desorption products at lower temperatures (approximately 250 °C) increased with alkyl chain length between C[n] = 8 - 16. TG-MS analysis showed that this was mostly due to the DHC of alkyl fragments. These compounds appear to have been largely overlooked in related literature.SWa-1, a clay containing greater concentrations of structural iron, showed higher T[max] values for n-alkylammonium surfactant thermal desorption than similarly exchanged SAz-1. This may be evidence of a current theory that structural iron acts as a radical trap. This is thought to significantly reduce the catalytic activity of the clay's acid sites until higher temperatures. The formulation of polystyrene-clay nanocomposites (PSCNs) by in-situ polymerisation led to various results pertaining to their thermal stability. The relative effectiveness of various initiator species for the production of the most thermally stable PSCNs was AIBN > BPO > SPS > APS > AIBA. Lower radical initiator and organic modifier concentrations led to the production of PSCNs with higher thermal stability. The relative effectiveness of these various organoclays for the production of more thermally stable PSCNs was MCBP-Cn > C15A > C20A " C10A. The preparation method was shown to be effective for producing exfoliated nanocomposites for up to 1 wt% of the various organoclays using AIBN and BPO as initiators. The MCBP-Cn PSCNs remained exfoliated up to 5 wt% , they also showed higher thermal stability when compared with the commercial products, which XRD results showed to remain stacked at organoclay loadings > 1 wt%.A novel one-pot synthesis method for the production of PSCN, by the in-situ polymerisation of PS in the presence of decanamide (an uncharged surfactant) and Na-MMT, was shown to be successful. Whereas, other novel PSCN formulations incorporating N-vinylformamide and the amphoteric surfactant foamtaine SCAB were shown to be encouraging but have, so far, had limited success.In contrast, the analysis of industrially produced unsaturated polyester-clay nanocomposites showed very little increase in the thermal stability of the material. Associated analyses indicated increased dimensional stability of the material, AFM analysis showed that imaging of the clay dispersal was possible by this macroscopic technique. Also, ATR-FTIR analysis of the UPR and UPCN, showed that although not exfoliated the silane modified-MMT had a good synergistic effect on the overall material by reducing the formation of combustion products.The thermal stability and associated studies of kaolin-phenylphosphonic acid (KPPA) complexes was also conducted. PPA was shown to intercalate the kaolin crystal structure forming an expanded phase that exhibited remarkable thermal stability (Tmax = 660 °C). 31P MAS NMR of all the KPPA samples showed three peaks (at +1.2, -3.7 and -7.3 ppm) which represented PPA existing in three non-equivalent bonding states at the kaolin surface. The high thermal stability of these hybrid materials was evident from these studies. This research into the use of covalently bound intercalates in nanocomposite manufacture signifies the necessity for further research.