Solvent Effects under High Pressures. IV. A Procedure for the Estimation of Solvation in the Transition State

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Abstract
The rate constants and activation parameters were measured for the reaction of pyridine with benzyl bromide in various solvents. The rate constants were better correlated to the activation volumes than to the activation entropies. The linear free-energy relationships were observed in the plots of the logk values of some Menschutkin reactions vs. the logk values of the present reaction in various solvents. Corresponding to their good correlations between the values of log k and of their pressure derivatives for the present reaction, the values of (z·ΔP), which are the slopes of the plots of ΔV0\eweq vs. KV0, increased with the increase in the slopes of the above linear free-energy relationships. The activation volumes in various solvents are linearly correlated to their pressure derivatives. An equation which predicts the relationship has been derived. Using this equation, the solvation number in the activated complex and the average pressure within its cosphere have been estimated to be ca. 4 and 910 (kg. cm−2) respectively. Based on these results, discussions have been given on the solvation in the transition state for the present reaction.

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