Radical-molecule reaction CH₂Cl + NO₂: A mechanistic study

The radical-molecule reaction mechanism of CH₂Cl with NO ₂ has been explored theoretically at the B3LYP/6-311G(d,p) and MC-QCISD (single-point) levels of theory. Our results indicate that the title reaction proceeds mostly through singlet pathways, less go through triplet pathways. The initial association between CH₂Cl and NO₂ is found to be the carbon-to-nitrogen attack forming the adduct a H ₂ClCNO₂ with no barrier, followed by isomerization to b₁ H₂ClCONO-trans which can easily convert to b ₂ H₂ClCONO-cis. Subsequently, the most feasible pathway is the C-Cl and O-N bonds cleavage along with the N-Cl bond formation of b (b ₁, b₂ ) leading to product P₁ CH₂O + ClNO, which can further dissociate to give P₅ CH₂O + Cl + NO. The second competitive pathway is the 1,3-H-shift associated with O-N bond rupture of b₁ to form P₂ CHClO + HNO. Because the intermediates and transition states involved in the above two favorable channels all lie below the reactants, the CH₂Cl+NO₂ reaction is expected to be rapid, as is confirmed by experiment. The present results can lead us to understand deeply the mechanism of the title reaction and may be helpful for further experimental investigation of the reaction.