Polar effects. Part 12. Inductivity and carbon participation in the solvolysis of 4-substituted 2-adamantyl arenesulfonates

The rate constants (log k) for the solvolysis of 4^e-substituted 2^e- and 2^a-adamantyl p-nitrobenzenesulfonates 14 and 15 , respectively, in 80% EtOH correlate linearly with the respective inductive substituent constants σ. Therefore, relative rates are controlled by the I effect of the substituents at C(4). The derived reaction constants, or inductivities, ρ_I of −0.80 and −0.64 for the series 14 and 15 , respectively, are far smaller than those previously determined for 6-substituted 2-norbornyl and 2-bicyclo2.2.2]octyl sulfonates, in which the partial structure containing the substituent and the leaving group is the same. The ratio of the retained and inverted adamantanols obtained upon hydrolysis of the series 14 falls from 2.85 for R = CH₃ to ca. 1 for R = CN, i.e. as the substituent at C(4) becomes more electron-attracting. In the 2^a-series 15 this ratio is uniformly higher. These findings confirm that the 2-adamantyl cation is weakly bridged and that through-space induction in carbocations involves graded bridging of the cationic center by neighboring C-atoms.