Acid-catalysed cleavage of 4-halonortricyclenes in deuterated medium; evidence that the norbornyl cation is an unsymmetrical species

We have determined the endo:exo deuterium ratios at C(6) of the exo-acetates obtained by D 2 SO 4 -catalysed cleavage of nortricyclene (4a), 4-chloronortricyclene (4b), 4-bromonortricyclene (4d), and 4-iodonortricyclene (4e). That the ratios are 1.09 ± 0.03, 1.30 ± 0.04, 1.40 ± 0.02, and 1.48 ± 0.02 for ring-opening of 4a, 4c, 4d, and 4e, respectively, establishes that the norbornyl cation is an unsymmetrical rapidly-equilibrating species.