The thermal decomposition of methane. III. Methyl radical exchange in CH<sub>4</sub>–CD<sub>4</sub> mixtures

Chen, C.-J.; Back, M. H.; Back, R. A.

doi:10.1139/v77-229

Cited by 9 publications

(6 citation statements)

References 5 publications

(9 reference statements)

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Section: Resultsmentioning

confidence: 99%

Whence the Energy Term of the Rate Constant?

Zavitsas

2010

J. Phys. Chem. A

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Insights into the causes of energy barriers to reactions are obtained from our E* model for hydrogen abstractions. Results of the model are in good agreement with all eight experimentally studied symmetrical reactions of the type X-H + (*)X --> X(*) + H-X. The E* energy is broken down into three components: energy needed to overcome triplet repulsion between the terminal Xs, energy needed to bring the H-X bonds to their transition state distances, and energy gain by the resonance stabilization of delocalization of the odd electron over three atoms. The strength of the X-H bond is a minor factor. The conclusion that triplet repulsion is a major factor is supported by the London equation and by results of recent high level theoretical calculations. The E* model requires inputs of bond dissociation energies, bond lengths, and infrared stretching frequencies of X-H and X-X. Some reported failures of E* are shown to have been caused by use of input values subsequently found to be incorrect.

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Section: Resultsmentioning

confidence: 99%

Whence the Energy Term of the Rate Constant?

Zavitsas

2010

J. Phys. Chem. A

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“…[5] and [6] the important measurement for the determination of the ratio of rate constants is the ratio of rates in the presence and absence of the additive. Two approaches to this measurement have been adopted and have been described in previous studies (10)(11)(12).…”

Section: Resultsmentioning

confidence: 99%

“…[5] and [6] become Plots of the results according to these equations are shown in Fig. 2B and the ratios of rate constants kll/k3 and k12/k4 obtained from these plots are included in Table 2.…”

Section: B Toluenementioning

confidence: 99%

Rate constants for abstraction of hydrogen from benzene, toluene, and cyclopentane by methyl and ethyl radicals over the temperature range 650–770 K

Zhang¹,

Ahonkhai²,

Back³

1989

Can. J. Chem.

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. Can. J. Chem. 67, 1541 (1989). Rate constants for the abstraction of hydrogen from benzene, toluene, and cyclopentane by methyl and ethyl radicals have been measured relative to the corresponding abstraction reaction from ethylene. The method is based on the effect on the rates of formation of methane and ethane of the addition of small quantities of the reactants to the thermal chain reactions of ethylene in the temperature range 650-770 K. Taking the following values of the rate constants for the reference reactions (R = 8.314 J mol-' K-I):[4] C2Hs + C2H4 -* C2H6 + C2H3; log k4 (L mol-' s-I) = 8.2 t-0.2 -(62200 t-3000)/2.3RT the following rate constants were measured:[8] C2Hs + C6H6 -* C2H6 + C6HS; log kg (~m 0 1 -' S-') = 8.8 i 0.3 -(62200 i 5000)/2.3RT [ l l ] CH3 + C7Hg + CH4 + C7H7; log kll (L mol-' s-') = 7.4 i 0.5 -(29000 ? 7000)/2.3RT[12] C2HS + C7H8 'C2H6 + C7H7; log k12 ( L m~l -' s -~) = 7.7 * 0.5 -(37000 ? 7000)/2.3RT[15] CH3 + c-CsHlo -CH4 + c-C5Hg; log klS (L mol-' s-I) = 8.3 2 0.5 * (36000 ?7000)/2.3RTThe values of the activation energies are discussed in relation to the dissociation energies of the C-H bonds in the reactants.

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“…Experiments with CD4/CH4-mixtures at temperatures in between have been carried out by Chen [32] in a static system with mass spectrometric product analysis. The resulting mean rate coefficient is also plotted in Fig.…”

Section: Reaction (2)mentioning

confidence: 99%