Steric and electronic effects of the alkyl group on the activation parameters of the water substitution reaction of some cobaloximes

The activation parameters for the water substitution reactions of some organocobaloximes with thiourea in aqueous solution at I = 1 M (NaNO₃) are reported and discussed. Scatter in an isokinetic plot indicates that more than one interaction mechanism is at play. The ΔH* values are shown to be influenced by the electron withdrawing power and by the steric bulk of alkyl group. The influence of these factors on ΔS* cannot be rationalized.