The effects of solvent and substituents upon the ionization of phenols
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The “dissociation constants” of a series of 4-substituted-phenols, 4-substituted-2,6-dichlorophenols, and 4-substituted-2,6-dimethylphenols have been measured potentiometrically in a variety of solvents. Excellent linear Hammett plots are obtained for each series in all solvents. The effects of changing solvent upon the Hammett ρ values for each of these three series are deduced from these measurements. As the “solvating power” of the solvent is reduced ρ for each series increases because of the increased demand placed on the 4-substituent for dispersal of the anionic charge. Within each solvent ρ is greater for the 2,6-disubstituted-phenols than for the unhindered phenols. The 2,6-substituents hinder solvation and tis increases the demand for anionic charge dispersal by the 4-substituent. 2,6-Dichloro- or 2,6-Dimethyl-substitution is found to hinder solvation of the phenoxide ion even in water. The solvent-dependence of the Hammett σρ values is discussed and some attempt is made to interpret the shape of the potentiometric titration curves in different solvents.