Symmetric and Unsymmetric Bifurcating Surfaces of Ambimodal Reactions: Origin of Electronic Behavior in Post-Transition State Bifurcation

Abstract

Ambimodal reactions are distinctive in their ability to produce multiple products from a single transition state (TS) through bifurcation of the potential energy surface (PES), the mechanism of which is inadequately described by conventional kinetic theory. This report gains a crucial insight into the electronic structure and behavior underlying the dimerization of azacyclopentadienone to resolve ambiguity in their complex mechanisms. The result rationalizes the critical interplay of electrons on the PES that governs the nature of bifurcation and the duration of the reaction. Reactions on symmetric surfaces have a high degree of asynchronicity and proportional bidirectional electron delocalization, leading to longer reaction durations. The transition of reactant to the major product on unsymmetric PES is streamlined and independent of competing trajectories, and electron flow is synchronous. The outcomes provide a proof of concept to minimum energy path (MEP) bifurcation from the valley ridge inflection point on symmetric surfaces but not on unsymmetric surfaces based on the transformation of intrinsic bond orbitals. Despite this, a minor product is formed through the bifurcation of the MEP, even on an unsymmetric surface, following a more asynchronous yet concerted mechanism. The overall electron interplay is decisive for the stabilization of TS and determining the kinetic selectivity of conventional or bifurcated pathways and not on the emergence of ambimodal character.