Theoretical study on the mechanism of the CH + CH₃OH reaction

The possible reaction mechanism of CH radical with CH₃OH is investigated theoretically by a detailed potential energy surface calculation at the B3LYP/6-311G(d,p) and CCSD(T)/6-311+G(d,p) (single-point) levels. Various possible reaction paths including three kinds of insertion reaction and two kinds of H-abstraction reactions are considered. Among them, the most feasible pathway should be a CH radical attacking on the lone pair of the oxygen atom in CH₃OH to form the anti C-O complex a₁, followed by a CH inserting into the O-H bond to form the low-lying methoxymethyl radical a₃. Starting from a₃, the most competitive reaction pathway is the direct C-O single bond fission leading to the product P₁ CH₂O + CH₃. The other reaction pathways are less competitive due to thermodynamical or kinetic factors. Furthermore, our calculation results show that, in terms of potential energy surface, the title reaction involves all the main features of both CH + H₂O and CH + CH₄ reactions; however, the reaction mechanism of CH with CH₃OH may be more similar to that of CH + H₂O. Our results may be helpful for understanding the mechanism of a CH radical insertion reaction.