Theoretical kinetic studies for low temperature oxidation of two typical methylcyclohexyl radicals

Abstract

To improve the understanding of low temperature oxidation of methyl cyclohexane, the potential energy surfaces for O2 addition to two of its radicals (tcy-C6H10(*)CH3 with a tertiary radical site and ortho-cy-C6H10(*)CH3 with a secondary radical site in the ortho position to the methyl substitution) have been investigated by high level quantum chemical calculations. The reaction kinetics was studied by the ab initio transition state theory based on master equation methodology. The relationship between low temperature oxidation reactivity and molecular structures was explored, typically in terms of the barrier heights of 1,5 H-shift for peroxy radicals. The computed phenomenological rate constants reveal that the ROO stabilization dominates the fates of two methyl cyclohexyl radicals reacting with O2 at pressures higher than 1atm over the studied temperature range. The balance between ROO stabilization, HO2 elimination, QOOH stabilization, and OH formation was further revealed by branching ratios of these four types of reactions. This study extends kinetic data for cyclic alkanes oxidation in a wide range of pressure and temperature.