Equilibrating system of 2-methylbenzonorbornen-2-yl type cations

The nature of the changes in the ¹³C NMR spectra of the 2-methylbenzonorbornen-2-yl carbocation caused by the substitution of deuterium for hydrogen in the methyl group and by temperature variation suggests that in fact this cation represents a system of two or more species with differing extents of π-bridging separated by a very low energy barrier.