SUBSTITUENT EFFECTS ON THERMODYNAMIC FUNCTIONS OF PROTON DISOCIATION OF PARA-SUBSTITUTED ANILINIUM IONS

Thermodynamic acidity constants of the para-methoxyanilinium, para-chloroanilinium, para-bromoanilinium, para-iodoanilinium, and para-nitroanilinium ions have been measured by a combined e.m.f.- spectrophotometric technique within the temperature range 5-60°, and the standard enthalpies and entropies of proton dissociation have been calculated. The results are discussed in terms of Hepler's dichotomised enthalpy approach and a new method of calculating solvation parameters in this theory is derived and tested.