Degradation of alkyl radicals via C-H bond dissociation: Kinetic parameters and transition state geometry

Abstract

Experimental data on the decomposition of alkyl radicals in the gas phase of the type RCH2C.H2 → RCH=CH2 + H. were analyzed in terms of the method of crossing parabolas. The parameters characterizing such decomposition were calculated. The activation energy Ee0 for the thermoneutral degradation reaction was shown to depend on the radical structure. The degradation of the radicals RCH2C.H2, CH2=CRC.H2, PhC.HCH2R, and CH2=C.CH2R is characterized by Ee0 = 81.6, 85.9, 85.9, and 115.2 kJ mol−1, respectively. The semiempirical algorithm for calculation of geometric parameters of the transition state for reactions of hydrogen atom addition to olefins was extended to the degradation reactions of alkyl, aminoalkyl, and ketyl radicals. The kinetic (activation energies) and geometric (interatomic distances in the transition state) reaction parameters were calculated for the decomposition reactions of various alkyl, alkylaromatic, aminoalkyl, and ketyl radicals.