Mechanistic Insights into the Proton Transfer and Substitution Dynamics of N-Atom Center Reactions: A Study of CHO with NHCl.

Bimolecular substitution reactions involving N as the central atom have continuously improved our understanding of substitution dynamics. This work used chemical dynamics simulations to investigate the dynamics of NHCl with N as the central atom and the multiatomic nucleophile CHO and compared these results with the F + NHCl reaction. The most noteworthy difference is in the competition between proton transfer (PT) and the S2 pathways. Our results demonstrate that, for the CHO + NHCl system, the PT pathway is considerably more favorable than the S2 pathway. In contrast, no PT pathway was observed for the F + NHCl system at room temperature. This can be attributed to the exothermic reaction of the PT pathway for the CHO + NHCl reaction and is coupled with a more stable transition state compared to the substitution pathway. Furthermore, the bulky nature of the CHO group impedes its participation in S2 reactions, which enhances both the thermodynamic and the dynamic advantages of the PT reaction. Interestingly, the atomic mechanism reveals that the PT pathway is primarily governed by indirect mechanisms, similar to the S2 pathway, with trajectories commonly trapped in the entrance channel being a prominent feature. These trajectories are often accompanied by prolonged and frequent proton exchange or proton abstraction processes. This current work provides insights into the dynamics of N-centered PT reactions, which are useful in gaining a comprehensive understanding of the dynamics behavior of similar reactions.