Dissociation of 1-butene, 3-methyl-1-butene, and of 3,3-dimethyl-1-butene and the resonance energy of the allyl, methyl allyl and dimethyl allyl radicals

Abstract

The rates of dissociation of 1-butene, 3-methyl-1-butene and of 3,3-dimethyl-1-butene into a methyl and an allylic radical have been determined from the rates of formation of primary methane when these compounds are thermally decomposed at temperatures in the range 657–766 K and pressures between 1 and 400 Torr. Surface effects which influence the rate of formation of methane at low pressures become unimportant at high pressures. The limiting high pressure rate constants can be represented by k_∞(C4H8)= 10^(16.3±0.3) exp [(–36 000±500)/T] s^–1, k_∞(C5H10)= 10^(15.9±0.3) exp [(–34 600±450)/T] s^–1, k_∞(C6H12)= 10^(16.9±0.3) exp [(–34 500±450)/T] s^–1. The activation energies lead to values of 12.4±1.8, 13.5±1.8 and 14.8±1.8 kcal mol^–1 for the resonance energies of the allyl, methyl allyl, and dimethyl allyl radicals respectively, assuming in each case that the activation energy for radical recombination is zero.