Theoretical mechanistic study on the radical-molecule reaction of CH ₂OH with NO₂

The complex singlet potential energy surface for the reaction of CH ₂OH with NO₂, including 14 minimum isomers and 28 transition states, is explored theoretically at the B3LYP/6-311G(d,p) and Gaussian-3 (single-point) levels. The initial association between CH ₂OH and NO₂ is found to be the carbon-to-nitrogen approach forming an adduct HOCH₂NO₂ (1) with no barrier, followed by C - N bond rupture along with a concerted H-shift leading to product PI (CH₂O + trans-HONO), which is the most abundant. Much less competitively, 1 can undergo the C-O bond formation along with C-N bond rupture to isomer HOCH₂ONO (2), which will take subsequent cis - trans conversion and dissociation to P₂ (HOCHO + HNO), P₃ (CH₂O + HNO₂), and P₄ (CH₂O + cis-HONO) with comparable yields. The obtained species CH₂O in primary product P₁ is in good agreement with kinetic detection in experiment. Because the intermediate and transition state involved in the most favorable pathway all lie blow the reactants, the CH₂OH + NO ₂ reaction is expected to be rapid, as is confirmed by experiment. These calculations indicate that the title reaction proceeds mostly through singlet pathways; less go through triplet pathways. In addition, a mechanistic comparison is made with the reactions CH₃ + NO₂ and CH₃O + NO₂. The present results can lead us to deeply understand the mechanism of the title reaction and may be helpful for understanding NO₂-combustion chemistry.