Substituent effects on ionization constants as a predictive tool of coordinating ability

The ionization equilibria of a set of ortho, meta, and para substituted benzoic acids have been studied by spectrophotometric and potentiometric methods. A dual substituent analysis of the obtained ionization constants is presented, according to the Swain and Lupton procedure. This analysis allows to assign the weight of field and resonance contributions to equilibrium constants and, furthermore, it greatly contributes to forecast the effect of substituents on other correlated properties.