Unconventional Pathways in Nitrogen-Centered SN2 Reactions: From Roundabout to Hydride Transfer.

Abstract

The mechanisms and dynamics of bimolecular nucleophilic substitution (SN2) reactions are complex and influenced by the nature of the central atom. In this study, we explore SN2 at a nitrogen center (SN2@N) by investigating the reaction of chloramine (NH2Cl) with methoxide ion (CH3O-) using ab initio classical trajectory simulations at the MP2(fc)/aug-cc-pVDZ level of theory. We observe that, in addition to the expected SN2 product formation (CH3ONH2 + Cl-), a high-energy proton-transfer pathway leading to CH3OH and NHCl- dominates, with near-quantitative agreement between simulations and experimental data. Notably, we identify a novel hydride-transfer pathway yielding NH3, H2CO, and Cl-, revealing alternative reactivity channels previously uncharacterized in nitrogen-centered SN2 reactions. Mechanistic analysis uncovers unconventional roaming-mediated and roundabout pathways alongside the traditional direct rebound and indirect mechanisms. Additionally, an umbrella inversion of the NH2 group resulting in retention of configuration in the CH3ONH2 product was observed in a fraction of trajectories.