Hyperconjugation. II. The Competitive Bromination of Benzene and t-Butylbenzene

Berliner, Ernst; Bondhus, Frances J.

doi:10.1021/ja01182a118

Cited by 32 publications

(5 citation statements)

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“…The C-C bond dissociation energy (kJ/mol) in the main chain of trimers. The above results indicate that the benzene ring and the vinyl groups have great influences on the BDE of the C-C bond on the main chain, as the benzene ring or the C=C double bond and C are connected with single bonds to form a hyperconjugation effect [39,40]. Therefore, the BDE of the C-C single bond adjacent to the benzene ring or the C=C double bond is decreased, where the low BDE bond is easily broken during the pyrolysis process.…”

Section: Analysis Of Bond Dissociation Energy By Dftmentioning

confidence: 90%

Multiscale Simulation on Product Distribution from Pyrolysis of Styrene-Butadiene Rubber

et al. 2019

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Pyrolysis of styrene-butadiene rubber receives renewed attention due to its application in tackling the waste tire disposal problem while allowing energy recovery. The density functional theory calculation (DFT) and ReaxFF molecular dynamics simulation (MD) are adopted to study the pyrolysis process with the variation of temperature and pressure. The bond dissociation energies of intramonomer and intermonomer bonds in trimers with different linking methods are calculated by DFT, where the bond with low energy tends to break during the pyrolysis process. The following MD simulation shows the pyrolysis product distribution of chain segments in styrene-butadiene rubber, where bond breaking positions in MD agree well with corresponding results in DFT and experiment. The next nearest neighbor bonds (single bonds) connected with double bond or benzene usually have lower dissociation energies than other single bonds and prone to break during the pyrolysis process. And thus, the intermonomer bonds tend to break at relatively low temperatures (around 650 K in experiment) prior to intramonomer bonds, which result in the emergence of monomers. With the temperature increase, intramonomer bonds are broken and thus large fragments are further pyrolyzed into small ones (e.g., C2 and C). Besides, the pressure strongly influences the product distribution, where high pressures promote the occurrence of secondary reactions.

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Section: Analysis Of Bond Dissociation Energy By Dftmentioning

confidence: 90%

Multiscale Simulation on Product Distribution from Pyrolysis of Styrene-Butadiene Rubber

et al. 2019

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“…But this intuitive feeling is not reflected clearly in theory, and the next advance came in the recognition that the Baker-Nathan order reflects the differential effect of H-C versus alkyl-C hyperconjugation, and in the proposal (Ref. 17) that alkyl-C hyperconjugation played a major role in determining the total effect of the t-butyl group in a number of reactions, particularly but not exclusively those in which the Baker-Nathan order was evident ( Fig. 9).…”

Section: Hichch2mentioning

confidence: 99%

Hyperconjugation: intermediates and transition states in replacement and elimination

Mare¹

1984

Pure and Applied Chemistry

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A review is given of the development of experimental evidence for hyperconjugation in the form of electron-release to an unsaturated or electron-deficient centre from saturated H-C and CC bonds. This type of electron-release can contribute regioselectively to the reactivity of organic molecules, and need not involve breakage of the H-C or CC bond; under these circumstances, H-C and CC bonds make similar contributions to the observed effects of alkyl and derived groups, the relative contributions varying with reaction and solvent. In the limit, however, this form of electron-release can result in breakage of the hyperconjugating bond, and in such circumstances (as in transition states leading to proton-loss or 1,2-elimination), H-C bonds become much more effective than CC bonds because of the greater solvation of incipient protons than of incipient alkyl cations. Evidence for the corresponding hyperconjugation by H-O bonds comes especially, but not exclusively, from the relative rates of electrophilic aromatic replacements affected by H-0 and R-O groups. Recent experiments on the effects of these groups on nucleophilic replacements in aromatic side-chains show that the electron-releasing power of the H-O group is quite variable, and suggest that the impact of H-O hyperconjugation is more dependent on the reaction and the solvent than that of H-C hyperconjugation has been shown to be. Reaction pathways in the hydrolysis of R0.C6H2Br2.CHBr2 and RO.C6H3Br.CHBr2, which can lead to products both of replacement and of elimination, are discussed, and isotope effects in H-C and H-O hyperconjugation are compared.

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“…-C00C2H1 0.0026 0.0079 0.001 0.0037 (198) -F ---0.15 (21) -Cl 0.030 0.000 0.139 0.033 (21,246,247) -Br 0.037 0.000 0.106 0.030 (21,246,247) -I ---0.18 (21) -OH* ----10" -NO2* 0.24 X 10-s 2.75 X 10-6 0.03 X are available (32,60,182). Data for halogenation (16,17,18,28,29,61,62,90, 91, [223][224][225][226][227][228]243) and sulfonation (107,269,278,279) have been reported recently; e.g., for chlorination at ca. 25°C.…”

Section: Heterolytic and Homolytic Aromatic Substitutionmentioning

confidence: 99%

“…Brown (30), in 1940, showed by measurement of carbon dioxide evolution that the peroxide decomposition could be expressed by parallel firstand second-order reactions; i.e., if C represents the concentration of benzoyl peroxide, k[ and k'ii are constants, and t is time: ^= kíC + fciiC2 (15) di The approximate first-order kinetics was confirmed by some workers (11, 78), but Nozaki and Bartlett (235,236), in investigating a whole range of solvents, showed that in addition to unimolecular dissociation of the peroxide, now known (13,94,147, 148) to form two CeHBCOO• radicals, there was also a chain decomposition induced by the radicals derived from either the peroxide P or the solvent SH. The chain termination was thought to be by the recombination of the term /cnC3/2 to the rate equation 17, was the main cause of variation in the observed rate of decomposition from one solvent to another, and that these rates were in the order: Aromatic solvents2 < ethers < alcohols < phenols < amines (18) Some workers (53) believed that the similarity of the S• (Ar•) radicals, produced from a series of aromatic solvents, was the reason for the consistently small contribution that they made to the induced decomposition. Only in one instance (150) does it appear that the nature of the products from these aromatic systems has been considered and due reservation expressed concerning the solvent-radical mechanism.…”

Section: Homolytic Arylation Reactionsmentioning

confidence: 99%

“…Using the known partial rate factors for chlorobenzene, nitrobenzene, pyridine, and biphenyl (c/. table 18), and making the reasonable assumptions given in the footnote to table 20, the figures given in tables 20 and 21 may be evaluated for the reactivities of the isomers shown in formulas A, B, and C: X X ABC It is seen that the difference in reactivities of the phenylpyridines is small. Any experiment using a mixture of such compounds, e.g., that wdiich is formed on phenylation (cf.…”

Section: Application Of Principlementioning

confidence: 99%

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