Is the most stable gas-phase isomer of the benzenium cation a face-protonated π-complex?

Abstract

The recent suggestion, based on gas-phase experimental data, that the most stable isomer of protonated benzene has a face-protonated π-complex structure is not supported by our detailed computations which indicate that the π-complex is a second-order saddle point on the potential energy surface, lying 199 kJ mo–1 higher in energy than the well-established C2vσ-protonated structure.