Effects of substituents on activation parameters in the reactions of carboxylic acid derivatives with anionic and neutral nucleophiles

Abstract

Changes of activation parameters, ΔH^‡ and ΔS^‡, with σ constants of substituents in the reactions of carboxylic acid derivatives with anionic and neutral nucleophiles in various solvents give the δΔH^‡ and δΔS^‡ reaction constants which are linearly related for variations of substituents in substrate and nucleophile. The dependences obtained, δΔH^‡vs.δΔS^‡, allow estimation of the contribution of changes of the internal enthalpy, δΔH^‡_int, to the enthalpy reaction constant, δΔH^‡, which give a single linear dependence on the Hammett ρ reaction constants. The results obtained show that the substituent effects on the charge development in the transition state are governed by the magnitude of δΔH^‡_int.