Unconventional\nPathways in Nitrogen-Centered S<sub>N</sub>2 Reactions: From Roundabout\nto Hydride Transfer

The mechanisms and dynamics of bimolecular nucleophilic\nsubstitution\n(S<sub>N</sub>2) reactions are complex and influenced by the nature\nof the central atom. In this study, we explore S<sub>N</sub>2 at a\nnitrogen center (S<sub>N</sub>2@N) by investigating the reaction of\nchloramine (NH<sub>2</sub>Cl) with methoxide ion (CH<sub>3</sub>O<sup>–</sup>) using ab initio classical trajectory simulations\nat the MP2(fc)/aug-cc-pVDZ level of theory. We observe that, in addition\nto the expected S<sub>N</sub>2 product formation (CH<sub>3</sub>ONH<sub>2</sub> + Cl<sup>–</sup>), a high-energy proton-transfer pathway\nleading to CH<sub>3</sub>OH and NHCl<sup>–</sup> dominates,\nwith near-quantitative agreement between simulations and experimental\ndata. Notably, we identify a novel hydride-transfer pathway yielding\nNH<sub>3</sub>, H<sub>2</sub>CO, and Cl<sup>–</sup>, revealing\nalternative reactivity channels previously uncharacterized in nitrogen-centered\nS<sub>N</sub>2 reactions. Mechanistic analysis uncovers unconventional\nroaming-mediated and roundabout pathways alongside the traditional\ndirect rebound and indirect mechanisms. Additionally, an umbrella\ninversion of the NH<sub>2</sub> group resulting in retention of configuration\nin the CH<sub>3</sub>ONH<sub>2</sub> product was observed in a fraction\nof trajectories.