Solvent Dependence of Inductivity in the Solvolyses of Substituted Norbornyl p-Toluenesulfonates. Norbornanes,Part 14

A comparison of the solvolysis rates of the substituted 2-exo- and 2-endo -norbornyl p-toluenesulfonates 1, 2, 3 and 4 and the substituted 1- and 2-adamantyl sulfonates 9 and 10 , respectively, in 80% ethanol and 97% trifluoroethanol has shown that the sensitivity of rates to the I-effect of substituents, i.e. the inductivity of these compounds, varies strongly with structure, configuration and solvent. In 97% trifluoro-ethanol, a solvent of low nucleophilicity and high ionizing power, the inductivities of the 2-endo-norbornyl p-toluenesulfonates 2 and 4 as well as the inductivities of the adamantyl derivatives 9 and 10 were larger than in 80% ethanol. In contrast, the inductivity of the 2-exo-norbornyl p-toluenesulfonates 1 was practically unchanged. It was, therefore, concluded that the transition states for the former compounds are not, or only weakly, bridged, whereas the transition states for the 2-exo-norbornyl p-tolu-enesulfonates 1 involve graded bridging by C (6). These results confirm that, due to differential bridging strain, 2-norbornyl cations are anisotropic to polar effects.