Sulfonyl Chloride Kinetics. Part II. Solvolysis of a Series of Benzenesulfonyl Chlorides: An Unexpected Heat Capacity Variation

Abstract

First order rate constants for the solvolysis of a series of 4-X-benzenesulfonyl chlorides (where X = MeO, Me, Br, and NO 2 ) were measured by the conductance method in H 2 O over the approximate temperature range of 0 to 25°. Pseudothermodynamic parameters, ΔG ≠ , ΔH ≠ ΔS ≠ , and ΔC p ≠ were derived and the high accuracy of the rate constants enabled an estimation of dΔC p ≠ /dT.A trigonal bipyramidal transition state is favored for the nucleophilic attack which is probably by an S N 2 type mechanism. A novel explanation for the effect of 4-methoxy on ΔC p ≠ involves a temperature dependent water–solute interaction, which has general applicability to the behavior of 4-methoxy substituents.