Theoretical study on the mechanism of the CH₂F + NO₂ reaction

Despite the importance of the Fluoromethyl radicals in combustion chemistry, very little experimental information on their reactions toward stable molecules is available in the literature. Motivated by recent laboratory characterization about the reaction kinetics of Chloromethyl radicals with NO₂, we carried out a detailed potential energy survey on the CH ₂F + NO₂ reaction at the B3LYP/6-311G(d,p) and MC-QCISD (single-point) levels as an attempt toward understanding the CH₂F + NO₂ reaction mechanism. It is shown that the CH₂F radical can react with NO₂ to barrierlessly generate adduct a (H ₂FCNO₂), followed by isomerization to b₁ (H₂FCONO-trans) which can easily interconvert to b₂ (H₂FCONO-cis). Subsequently, Starting from b (b₁, b ₂), the most feasible pathway is the C - F and N - O1 bonds cleavage along with N - F bond formation of b (b₁, b₂) leading to P₁ (CH₂O + FNO), or the direct N - O1 weak-bond fission of b (b₁, b₂) to give P₂ (CH₂FO + NO), or the 1,3-H-shift associated with N - O1 bond rupture of b₁ to form P₃ (CHFO + HNO), all of which may have comparable contribution to the reaction CH₂F + NO₂. Much less competitively, b ₂ either take the 1,4-H-shift and O1 - N bond cleavage to form product P₄ (CHFO + HON) or undergo a concerted H-shift to isomer c₂ (HFCONOH), followed by dissociation to P₄. Because the rate-determining transition state (TSab₁) in the most competitive channels is only 0.3 kcal/mol higher than the reactants in energy, the CH ₂F + NO₂ reaction is expected to be rapid, and may thus be expected to significantly contribute to elimination of nitrogen dioxide pollutants. The similarities and discrepancies among the CH₂X + NO₂ (X = H, F, and Cl) reactions are discussed in terms of the electronegativity of halogen atom. The present article may assist in future experimental identification of the product distributions for the title reaction, and may be helpful for understanding the halogenated methyl chemistry.