Structures, energetics, and kinetics of H-atom abstraction from methyl propionate by molecular oxygen: Ab initio and DFT investigations

Abstract

Initial degradation of methyl propionate (MePr) through its reaction with triplet molecular (3Σg−) O2 was investigated using density functional theory (DFT) and ab initio CBS-QB3 calculations over temperature range 700–1600 K. Thermochemistry and kinetics of three hydrogen atom abstractions have been studied. These reactions encounter energy barriers of 44.17–48.10 kcal mol−1 at CBS-QB3. Rate coefficients of the studied channels were evaluated from transition state theory (TST) with tunneling correction. From kinetic and thermodynamic perspectives, the most favorable process is H-atom abstraction from the Cα position, followed by Cμ, and then Cβ position. This order is partially different for the reaction of MePr with singlet (1Δg) O2 where H-atom abstraction from the Cμ atom is the most preferable pathway, followed by Cα position, then Cβ position. The atom in molecules (AIM) theory in critical point and natural bond orbital (NBO) analysis was used to explain the existence of covalent interactions.