Thermodynamic Parameters Including Acid Dissociation Constants for Bromochlorophenols (BCPs)

This contribution reports standard gas-phase enthalpies of formation (Δ_fH°₂₉₈), entropies (S°₂₉₈), and heat capacities (C_p°(T)) for all plausible 64 bromochlorophenols (BCPs) at the M062X meta hybrid level using a polarized basis set of 6-311+G(d,p). Isodesmic work reactions served to calculate the standard enthalpies of formation for all bromochlorophenol molecules and several bromochlorophenoxy radicals. Standard entropies and heat capacities comprise correction terms due to the treatment of O-H bonds as hindered rotors. Values of the bond dissociation enthalpies (BDHs) of O-H bonds, calculated for a selected series of bromochlorophenols, vary slightly with the change in the pattern and degree of halogenation of the phenyl ring. A thermodynamic cycle facilitated the estimation of pK_a values, based on the calculated solvation and gas-phase deprotonation energies. We estimated the solvation energies of 19 out of 64 BCPs and their respective anions based on the integral equation formalism polarizable continuum model using optimized structures in the aqueous phase. Values of pK_a decrease significantly from around 9 for monohalogenated to around 3 for pentahalogenated phenols.