Substituent effects on the thermodynamic functions of proton dissociation of ortho-substituted anilinium ions

Abstract

Thermodynamic acidity constants of the ortho-methoxyanilinium, ortho-chloroanilinium, ortho-bromoanilinium, ortho-iodoanilinium, and ortho-nitroanilinium ions have been measured by a combined e.m.f.–spectrophotometric technique within the temperature range 10–60° and the standard enthalpies and entropies of proton dissociation have been calculated. An analysis of substituent effects on the thermodynamic functions and pK_a values is made in terms of two free-energy relationships and by comparison with the results for meta- and para-substituted anilinium anions.