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The dissociation of 3‐chloro‐1‐butene and the resonance energy of the chloro‐allyl radical
Author(s) -
Trenwith A. B.
Publication year - 1973
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550050107
Subject(s) - chemistry , activation energy , dissociation (chemistry) , reaction rate constant , bond dissociation energy , hydrogen atom , allylic rearrangement , radical , hydrogen , methyl radical , resonance (particle physics) , kinetics , organic chemistry , catalysis , atomic physics , alkyl , physics , quantum mechanics
Methane is a primary product of pyrolysis of 3‐chloro‐l‐butene at temperatures in the range 776–835°K, and from its rate of formation values have been obtained for the limiting high‐pressure rate constant of the reactionThese may be represented by the expression log [( k 1 ) ∞ /sec −1 ] = (16.7 ± 0.3) − (71.5 ± 1.5)/θ, where θ = 2.303 RT kcal/mole. Assuming a zero activation energy for the reverse reaction and that over the experimental temperature range the rates at which a methyl radical adds on to chlorobutene are comparable to those at which it abstracts hydrogen, the activation energy for the dissociation reaction leads to a value of 83.2 ± 1.9 ckal/mole for D (HCHClCH:CH 2 ) at 298°K. Taking D (HCHClCH 2 CH 3 ) = 95.2 ± 1.0 kcal/mole a value of 12.0 ± 2.1 kcal/mole is obtained for the resonance energy of the chloroallyl radical. This value in conjunction with resonance energies obtained in earlier work indicates that substitution of a hydrogen atom on the carbon atom adjacent to the double bond in the allyl radical leads to no significant variation in the allylic resonance energy.