SN1 reaction mechanisms of tert-butyl chloride in aqueous solution: What can be learned from reaction path search calculations and trajectory calculations for small hydrated clusters?

Abstract

The SN1 reaction mechanisms of tert-butyl chloride (t-BuCl) in aqueous solution were studied using a small hydrated cluster model, t-BuCl·(H2O)n (n = 1–3), and density functional theory calculations. Our explicit solvation model is combined with a polarizable continuum model. Reaction path search calculations yielded various transition state structures associated with configurations to form retained and inverted t-BuOH (t-BuOH2+) products, respectively. Intrinsic reaction coordinate (IRC) analyses revealed that the retention process occurs via a three-step mechanism comprising initial CCl elongation, subsequent translational motion of the Cl−·(H2O)n moiety, and finally CO bond formation, while the inversion process essentially occurs via a concerted mechanism. To further elucidate the differences in the reaction mechanism between retention and inversion, on-the-fly trajectories were integrated starting from the identified transition state structures. The calculated trajectories exhibited non-IRC dynamic behavior.