A Molecular Dynamics−Empirical Valence Bond Study of an SN2 Reaction at the Water/Chloroform Interface

Abstract

Using a recently developed empirical valence bond (EVB) model for the nucleophilic substitution reaction (SN2) in solution, we study the benchmark Cl− + CH3Cl reaction at the water/chloroform liquid/liquid interface. The reaction free energy profile is determined as a function of the reagents’ location relative to the interface. We find that the activation free energy is very sensitive to the reagents’ location and to the orientation of the nucleophilic attack. The barrier height at the interface is equal or slightly larger than the barrier in bulk water and approaches the value in bulk chloroform only when the solute is a few nanometers deep into the organic phase. We show that this is due to the ability of the nucleophile to keep part of its hydration shell. This suggests that for the catalytic effect of the nonpolar solvent to be appreciable, the nucleophile must be transferred away from the interface. The dynamical correction to the rate, the variation in the system’s electronic structure and other sy...