Substituent effects on the thermodynamic functions of ionization of metasubstituted anilinium ions

Abstract

Thermodynamic acidity constants of the meta-methoxyanilinium, meta- chloroanilinium, meta-bromoanilinium, and meta-iodoanilinium ions have been measured spectrophotometrically over the temperature range 5-50º and those of the meta-nitroanilinium ion over the temperature range 5-60º. The thermodynamic functions of ionization, ΔG₂₅, ΔH₂₅, ΔS₂₅, and ΔC_p,25, have also been calculated for each ion. For a series of seven meta-substituted anilinium ions the acidity constants show close obedience to the Hammett equation over the temperature range 10-50º with the reaction parameter p being a precise linear function of 1/T. The same reaction series also shows a well-defined isoequilibrium relationship of negative slope.