The Structure of the 2-Norbornyl Cation: The π-Complex and Beyond^,

Abstract

Calculations at Becke3LYP, MP2, and QCISD levels of theory are presented for different molecular structures of the 2-norbornyl cation (1). With the aid of the quantum theory of atoms in molecules (AIM) we show that 1 has a T-structure at the C6−C1−C2 face (we view it as a π-complex with a tetracoordinate carbon atom C6) and that the (“nonclassical”) bridged structure with a pentacoordinate C6, which is not a minimum on the potential energy surface, is only reached when the C6−C1 and C6−C2 internuclear distances are shortened to 165 pm. At the Becke3LYP/6-31G(d,p) level in the gas phase this bridged species is 7.25 kcal mol-1 higher in energy than the equilibrium optimized geometry. NMR calculations show that 13C chemical shifts of C1, C2, and C6 of the bridged 165 pm species differ significantly from the experimental values.