Theoretical study on the mechanism of the ¹CHCL + NO₂ reactions

The radical-molecule reaction mechanism of ¹CHCl with NO ₂ has been explored theoretically at the B3LYP/6-311G(d, p) and CCSD(T)/6-311G(d, p) (single-point) levels of theory. Thirteen minimum isomers and 29 transition states are located. The initial association between ¹CHCl and NO₂ proceeds most likely through the carbon-to-middle-nitrogen attack leading to an energy-rich adduct a (HClCNO ₂), which is found to be a barrierless process. Staring from a, the most feasible channel is to undergo a concerted O-shift and C - N bond rupture leading to product P₂ (NO + HClCO). The minor product pathways are the direct O-extrusion of a to P₃ (O + HClCNO-cis) as well as the 1,3-H-shift of a to isomer b (ClCNOOH) followed by a concerted OH-shift leading to d (HOClCNO), which will dissociate to product P₈ (NO + ClCOH) via C - N cleavage. Because the transition states and isomers involved in the most feasible channel all lie below the reactants, the title reaction is expected to be rapid, as is consistent with the measured rate constant at 296 K. The comparison with the analogous reactions ³CH₂ + NO ₂ are discussed. The present study may be useful for further experimental investigation of the title reaction.