Isomerization of the 2‐Norbornyl Carbocation

Abstract

AbstractIn order to elucidate the mechanism for the isomerization of the 2‐norbornyl carbocation into its most stable isomer, the 1,3‐dimethylcyclopentenyl carbocation, an extensive set of the possible isomers of C7H11+ has been generated. Each one of these may undergo a number of transformations, and location of these transition states provides a searchable graph, from which pathways may be identified. This reveals that the preferred route for isomerization of the 2‐norbornyl carbocation is not by ring opening of the non‐classical center as has been reported in the literature (with an activation energy of 33.2 kcal/mol), but is initiated by cleavage of the C3–C4 bond (23.5 kcal/mol). Further, no single mechanism is sufficient to describe the full sequence of isomerizations of the 2‐norbornyl carbocation to its most stable isomer, the 1,3‐dimethylcylcopentenyl carbocation, but rather a collection (> 109) of pathways.