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.