Thermodynamic constants of ionization processes by spectrophotometric methods: Meta-halogenophenols

Thermodynamic ionization constants over the temperature range 10–60° together with values for the standard free energy, enthalpy and entropy of ionization of m-chlorophenol, m-bromophenol and m-iodophenol are reported. These results in conjunction with an extensive collection of similar results from the literature show that substituent effects in the ionization of phenols are due primarily to entropy changes possibly involving a change of solvation state. In contrast to the free energies of ionization the entropies are well correlated by σⁿ values.