Second Order Saddle Points Dictate the Products of Electrocyclic Reactions

The conventional understanding of chemical reactions, primarily focused on one-dimensional minimum energy pathways, has been expanded in recent years to include phenomena like second order saddle points or bifurcations. In this study, we explore these intricacies within the context of electrocyclizations and present a novel approach that moves beyond the traditional view of activation barriers, revealing that second order saddle points are crucial in dictating the competition between disrotatory and conrotatory pathways. Our findings suggest opportunities to manipulate the competition between conrotatory and disrotatory pathways through geometric constraints, fundamentally altering the connectivity of the potential energy surface. Through the development of a minimal model Hamiltonian, we illustrate the generality of our findings and highlight the importance of the multi-reference nature of states near the second order saddle point. This study emphasizes the necessity of multi-reference methods and the need to conduct higher-dimensional explorations for competing pathways. It opens new avenues for systematic control of selectivity in electrocyclic reactions and offers a rich perspective on the complex interplay of steric considerations and electronic correlations.