Use of an improved ion–solvent potential-energy function to calculate the reaction rate and α-deuterium and microsolvation kinetic isotope effects for the gas-phase S<i>N</i>2 reaction of Cl−(H2O) with CH3Cl

Abstract

We present calculations of the rate constants and secondary kinetic isotope effects for the gas-phase SN2 reaction Cl−(H2O)+CH3Cl based on a new chloride–water potential-energy function that has been specifically converged for heavy-water isotope effects. The results are compared to new calculations employing five chloride–water potential-energy functions that have been developed for simulations of aqueous solutions. In all calculations the ClCH3Cl− solute intramolecular potential is taken from a previous semiglobal fit to ab initio calculations including electron correlation. We also examine two different intramolecular water potentials, and we examine the effect of treating the CH3 internal rotation at the ClCH3Cl−(H2O) transition state as a hindered rotation. Both the CH3/CD3 (α-deuterium) and H2O/D2O (microsolvation) kinetic isotope effects are studied.