Inductivity and Bridging in 2-Bicyclo[2.2.2]octyl Cations. Polar Effects, Part 11

The solvolysis rates and products of several 6‐substituted 2‐exo‐ and 2‐endo‐Bicyclo[2.2.2]octyl p‐toluenesulfonates, 12 and 13, respectively, are reported. Inductivity, as measured by the reaction constants ρI, is considerably less in the exo‐series 12 (ρI = −1.50) than in the corresponding 2‐exo‐norbornyl p‐toluenesulfonates 1 (ρI= −2.0). It is proposed that, for geometrical reasons, bridging of the cationic center C(2) by C(6) is not as strong in the bicyclooctane series 12 as it is in the norbornane series 1. On the other hand, inductivity is higher in the 2‐endo‐bicyclooctane series 13 (ρI= −1.0) than in the corresponding 2‐endo‐norbornane series 3 (ρI = 0.78), probably, because in the former case bridging of C(6) is less hindered by the departing anion. The relative yields of exo‐ and endo‐substitution products from the series 12 and 13, are in accord with graded bridging of C(6) in the incipient bicyclooctyl cations. But almost constant bridging of C(2) by C(7) is indicated in the ionization of the 2‐endo‐bicyclooctane series 13. Consequently, in the free unsubstituted bicyclooctane cation C(2) is bridged symmetrically by C(6) and C(7), in contrast to the current concept of ‘non‐classical’ two‐electron‐three‐center bonding.