Reaction mechanism of CHCl− + CSO: A theoretical study

The doublet potential energy surface (PES) for the reaction of CHCl− with CSO is explored at the B3LYP/6-311++G(d,p), B3LYP/6-311++G(3df,2p) and CCSD(T)/6-311++G(3df,2p) (single-point) levels. Various possible reaction pathways are probed. It is shown that the most favorable association between CHCl− and CSO is found to be middle-C attack forming CHClC(O)S−1 with no barrier. Starting from 1, the most feasible pathway is the concerted S-shift along with Cl-extrusion of 1 to form product P2(Cl− + SCHCO). The minor product channel is the concerted O-shift along with Cl-extrusion of 1 to generate product P1(Cl− + OCHCS). Further conversions of P1 may form P6(SCHCl− + CO). Because the isomers and transition states involved in the feasible pathways all lie below the reactant, the title reaction is expected to proceed very fast which is consistent with the measured large rate constant in experiment. Our calculated results may be helpful for understanding the mechanism of the title reaction.