Understanding the sequence of the electronic flow along the HCN/CNH isomerization within a bonding evolution theory quantum topological framework

The sequence of electronic flow rearrangement, as described in terms of electron pair distribution, driving the HCN/CNH isomerization is revisited within the framework of bonding evolution theory approach as provided by the application of Thom’s elementary catastrophe theory to the changes, along the intrinsic reaction coordinate, of the gradient vector field of the electron localization function (ELF). Results provides a unique description of the evolution of the molecular rearrangement in terms of seven structural stability domains featuring six bifurcations, i.e., HCN: 7-F ^† FF ^† UUF-0: CNH, which provide a more detailed rationalization for the recent observation for unusual features concerning the electronic reaction force and force constant profiles of this process. Indeed, it is also revealed that the extremes of the electronic reaction flux profile (i.e., the negative of the instantaneous change of the chemical potential along the reaction path) are associated with the key relevant catastrophes, a fact that highlights the relevance that such a perturbative-based reactivity descriptor exhibits in connection with the study of abrupt changes in the gradient field of the ELF along a given reaction path, and hence, in the interpretation of the electronic activity along the course of chemical reactions.