TRANSITION-STATE STRUCTURES FOR SOLVOLYSIS OF METHANESULFONYL CHLORIDE

Solvolyses of methanesulfonyl chloride (CH3SO2Cl) in water and methano l have been studied theoretically using ab initio self-consistent reac tion field (SCRF) molecular orbital method. All stationary structures including transition state on the potential energy surface in solution have been found and compared with the gas phase structures. The overa ll reaction occurs via a concerted S(N)2 mechanism with a non-cyclic t rigonal bipyramidal transition state, and the activation barrier is lo wered significantly in solution. The transition state for the hydrolys is reaction is looser than that for the methanolysis reaction, and thi s is in accord with the experimental findings that an S(N)2 type mecha nism, which is shifted toward an S(N)1 process or an SAN process in th e hydrolysis and alcoholysis reaction, respectively, takes place. The catalytic role of additional solvent molecules appears to be a purely general-base catalysis based on the linear transition structures. Expe rimental barrier can be estimated by taking into account the desolvati on energy of nucleophile in the reaction of methanesulfonyl chloride w ith bulk solvent cluster as a nucleophile.