The Never-Ending Tales of 2-Norbornyl Carbocation: Heavy Atom Tunneling, Classical versus Nonclassical Behavior, and the Effect of Electric Fields

Decades of intense debate have surrounded the question of whether the 2-norbornyl cation has a classical or nonclassical structure, that is, if the charge is localized in a single carbocation or if the charge is distributed in a three-center-two-electron bond. Our computations corroborate that the parent system is nonclassical, but it can vary depending on the substituents. In the cases where the substitutions form a classical structure, we studied whether the degenerate Wagner-Meerwein carbon shift involves quantum tunneling. If so, the molecule will not stay fixed in one of the two enantiomers, but it will continuously rearrange even close to the absolute zero. Additionally, we explored how an oriented external electric field influences the structures, activation energies, and tunneling rates of the cations, and whether it is possible to tune their stabilities and reactivities under external perturbations.