Access to spiro(bicyc1o [ 2.2.1 ] heptane3,l '-cycloprop-6-yl) derivatives was gained from the alkene spiro(bicyclo [ 2.2.1 ] hept-Cene-2,l '-cyclopropane via separation of positional isomers. Spiro(bicyc1o 12.2.1 ] -2,l'cycloprop-exo-6-yl) p-toluenesulphonate (10) and spiro(bicyc1o [2.2.1] heptane-2,l'-cycloprop-exod-yl) trifluoroacetate were found to solvolyse faster than the analogous exo-2-norbornyl esters, as predicted by theory. Ion-pair recombination, with the formation of tricyclo [4.2.1.@*'] non-3-yl p-toluenesulphonate, accounts for previous failures to assess the true reactivity of 10. An intervening bridged carbocation (3), labelled with deuterium, was shown to achieve equivalence of C-1 and C-6 prior to ring expansion. The rate of the formal Wagner-Meerwein rearrangement is estimated to be of the order of molecular vibrations, thus supporting the symmetrical bridged structure of 3. Methyl substitution at C-6 was found to direct nucleophilic attack exclusively to the tertiary carbon, and ring expansion preferentially to the secondary carbon. An equilibrating pair of 6(1)methylspiro(bicyc1o [ 2.2.1 ] heptane3,l' -cycloprop-6-yl carbocations is thought to explain these observations most reasonably.