An ab initio MO study on the hydrolysis of methyl chloride

The methyl chloride hydrolysis in aqueous solution is a typical S(N)2 reaction. 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 which up to 13 solvent water molecules were explicitly considered. The precursor complex, transition state, product complex and final complex were detected for each of the systems. It was found that the attacking H2O molecule kept two hydrogen atoms at the transition state and the proton transfer from the attacking water to the water cluster began to occur after the transition state for each of the systems. The solute and solvent kinetic isotope effects (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 kinetic isotope effects quite well. In this system, CH3Cl is surrounded by 13 water molecules without any apparent vacant space. The 13 water molecule system produces a reasonable picture of the hydrolysis both in terms of its structure and energetics. (C) 1999 Elsevier Science B.V. All rights reserved.