Solvolytic reactions solvation effects

The unimolecular reaction of the ion aggregate follows a similar course and the intermediate faces the same three possibilities for reaction. The rate of bond fission will not necessarily be the same as that of the free ion because the solvation environment has changed. We see this effect in the ion pair-catalyzed solvolytic reactions (7). In addition, since the reagent Y is in position before the five-coordinate intermediate is formed, the path by which X re-enters the coordination shell becomes less probable as a result of more effective competition by Y, and the rate is increased. 

PhaCHBr, and 2-bronio-2-methyladamantane reveals dispersion which has been attributed to negative effects of nucleophilic solvation in the protic solvents. Arguments in support of formation and deprotonation of solvent-separated ion pairs are consistent with application of the generalized elimination rule to explain solvolytic dehydrobromination reactions of vicinyl dibromides, 4-bromo-4-bromomethyltetrahydropyran and 3,4-dibromo-4-methyltetrahydropyran, by the action of AcOH-AcONa and AcOH-NEts the regiochemistry reported is contrary to that predicted by the variable transition-state theory. ... 

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