Étude théorique des réactions d'abstraction d'hydrogène , avec R, X≡H, CH<sub>3</sub>, NH<sub>2</sub>,OH et F

Leroy, Georges; Sana, M.; Tinant, Anne

doi:10.1139/v85-248

Cited by 76 publications

(53 citation statements)

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“…[I]. Relations between such activation energies and bond dissociation energies have often been discussed and were recently examined in detail for small radicals such as methyl (24). The authors developed a semiempirical procedure to calculate activation barriers for hydrogen-abstraction reactions and showed that these barriers were related to the overall energy change in the reaction.…”

Section: Discussionmentioning

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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Section: Discussionmentioning

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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“…Therefore, x(T) depends not only on the imaginary frequency that characterizes the transition structure (vz), but also on the transition barrier (AE') and the reaction energy (AE,). Such an approach is not "exact," but usually gives results that agree in a qualitative manner with experimental data [25].…”

Section: The Kineticsmentioning

confidence: 99%

Early stages of LiX, BeH₂X, and BH₃X pyrolysis (X stands for NH₃ or OH₂): A theoretical study of weak dative complex stability

Sana

Leroy

1993

Int J of Quantum Chemistry

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In this work, we study theoretically the thermal decomposition of weak dative complexes (namely, the complexes between BH3, BeH2, or LiH and ammonia or water). The most accurate calculations have been carried out at the ~~4sdtq/6-311+ +G(3df,2p) level on MP2fu11/6-31c** fully optimized geometries. The transition structures for hydrogen evolution are described. The rate constants were obtained using conventional transition-state theory. Stability conditions for the complexes were considered. Water complexes are less stable than are the corresponding ammonia derivatives. Lithium complexes seem to be very unstable. It seems that beryllium compounds could be synthesized. Borane derivatives are known experimentally. We find, as observed, that the first hydrogen evolution occurs only above room temperature. Iminoborane seems not to be easily accessible under pyrolysis conditions. Other reactions require less activation energy. Finally, the early stages of the ammonia-borane pyrolysis and paths to open-chain polymers as well as to cyclic structures are described. 0 1993 John Wiley & Sons, Inc.

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“…The relation between activation energy and bond dissociation energy for a series of similar reactions has been discussed many times, particularly for hydrogen atom abstraction reactions. Recently a simple correlation has been described for such reactions involving small radicals (16 where E is the activation energy for the reaction and D l and D2 are the C-H bond dissociation energies for AH and CH4, respectively. For reaction [4], taking D l = 100 kcal mol-' and D2 = 104 kcal mol-I , E = 11.7 kcal mol-' in good agreement with the value recommended by Kerr and Moss.…”

Section: 3rtmentioning

confidence: 99%

Relative rate constants for abstraction of hydrogen by methyl radicals from ethane and from ethylene

Ahonkhai¹,

Back²

1988

Can. J. Chem.

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This paper is dedicated to Professsor J . A . Morrison S. I. AHONKHAI and M. H. BACK. Can. J. Chem. 66,578 (1988). A method is described for the measurement of relative rate constants for abstraction of hydrogen by methyl radicals from ethane and from ethylene based on the effect of the addition of small quantities of ethane on the rates of formation of products in the thermal reactions of ethylene. The ratio of rate constants for reactions over the temperature range 673-733 K was given by the following expression: 3500 * 500 log k4lk3 = 0.0 2 0.1 + 2.3RT (R = 1.987 cal mol-I deg-I). Using a value of k4 from the literature the following expression was obtained for k3, over the same range of temperature:It was concluded that a previous measurement of k3 in a lower range of temperature was too close to the value of k4

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Étude théorique des réactions d'abstraction d'hydrogène , avec R, X≡H, CH₃, NH₂,OH et F

Cited by 76 publications

References 5 publications

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

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

Early stages of LiX, BeH₂X, and BH₃X pyrolysis (X stands for NH₃ or OH₂): A theoretical study of weak dative complex stability

Relative rate constants for abstraction of hydrogen by methyl radicals from ethane and from ethylene

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Étude théorique des réactions d'abstraction d'hydrogène , avec R, X≡H, CH3, NH2,OH et F

Cited by 76 publications

References 5 publications

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

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

Early stages of LiX, BeH2X, and BH3X pyrolysis (X stands for NH3 or OH2): A theoretical study of weak dative complex stability

Relative rate constants for abstraction of hydrogen by methyl radicals from ethane and from ethylene

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Étude théorique des réactions d'abstraction d'hydrogène , avec R, X≡H, CH₃, NH₂,OH et F

Early stages of LiX, BeH₂X, and BH₃X pyrolysis (X stands for NH₃ or OH₂): A theoretical study of weak dative complex stability