Theoretical study on the thermal decomposition and isomerization of 3-Me-1-heptyl radical

Abstract

A detailed theoretical investigation on the thermal decomposition and isomerization of 3-Me-1-heptyl radical is performed at the ab initio CBS-QB3 level of theory. The calculation reveals that the detailed reaction mechanisms of 3-Me-1-heptyl radical mainly incorporate reversible intramolecular hydrogen atom transfer and the beta-site CC bond scission. The standard reaction enthalpies (ΔrH2980) and enthalpies of formation (ΔfH2980) are determined at the CBS-QB3 level of theory. All investigated decomposition reactions are generally endothermic, while most of the isomerization processes are exothermic. Among the hydrogen atom transfer processes, the 1,3- and 1,2-hydrogen atom migration (R5 and R6, respectively) are prohibited due to their high isomerization barriers, while the 1,6-(R2) and 1,5-hydrogen atom transfer (R3) are kinetically accessible (owing to their low ring strains in the cyclic transition states). Compared with the 1,5-hydrogen atom shift for the n-heptyl radical, the methyl-substitution increases the rate coefficient by a factor of about 3.0. The product distributions are predicted at different temperatures on the basis of the steady-state approximation (SSA). The ultimate and dominant products majorly include ethylene (C2H4), propylene (C3H6), 1-butylene (1-C4H8) and 2-hexene (2-C6H12) over the temperature range of 500–2500K.