Kinetics of proton transfer between metasubstituted benzoic acids and the carbinol base of crystal violet in toluene: Specific solvent effect-free metasubstituent effect on the reactivity of benzoic acids

Abstract

Apolar aprotic solvents are particularly advantageous for investigating the intrinsic metasubstituent effect free from complications of specific solvent effects. A kinetic study for toluene-phase proton transfers between meta-Me, F, Cl, Br, I, OMe, OPh, COPh, CF3, CN, NO2, H benzoic acids and Crystal Violet carbinol base has shown the forward rate constant (log k 1) the most appropriate reactivity parameter in toluene. log k 1 (toluene) as compared to other reported reactivity parameters in benzene or toluene have been found more sensitive to the metasubstituent effect. The regression results of the correlation of log k1 (toluene) of the acids according to the four dual substituent parameter models are statistically significant, and the best result has been obtained using Taft's model. The overall analysis reveals that metasubstituent's effect is exerted by a 65:35 pattern of its field and second-order resonance effects. The results further demonstrate that a metasubstituent's resonance effect is virtually a relayed universal field/inductive effect. © 2011 Wiley Periodicals, Inc.