An ab initio MO study on the hydrolysis of methyl chloride

The methyl chloride hydrolysis in aqueous solution is a typical S(N)2 react ion. Ab initio MO calculations (HF/3-21G, HF/6-31G, HF/6-31 + G*, HF/6-31 G** and MP2/6-31 + G*) were carried out on the hydrolysis of CH3Cl, in whi ch up to 13 solvent water molecules were explicitly considered. The precurs or complex, transition state, product complex and final complex were detect ed for each of the systems. It was found that the attacking H2O molecule ke pt two hydrogen atoms at the transition state and the proton transfer from the attacking water to the water cluster began to occur after the transitio n state for each of the systems. The solute and solvent kinetic isotope eff ects (KIEs) were calculated for all the systems and were compared with the experimental KIEs. The calculated results for the system with the 13 water molecules reproduced the experimental energetics and Various deuterium kine tic isotope effects quite well. In this system, CH3Cl is surrounded by 13 w ater molecules without any apparent vacant space. The 13 water molecule sys tem produces a reasonable picture of the hydrolysis both in terms of its st ructure and energetics. (C) 1999 Elsevier Science B.V. All rights reserved.