A MODEL FOR QUANTITATIVE-EVALUATION OF EQUILIBRIUM-CONSTANTS FOR HYDROGEN-BONDING IN POLAR APROTIC-SOLVENTS BASED ON INCOMPLETE DATA SETS RELATED TO DIFFERENT SOLVENTS

A general model is proposed for the evaluation of equilibrium constants for hydrogen bonding in polar aprotic solvents between weak acids and (a) solvents, (b) anions and (c) other acid molecules, based on incomplete literature data for hydrogen bonding in polar aprotic solvents or in carbon tetrachloride. The model is based on the apparent existence of 'unique', solvent-independent equilibrium constants, K(u), for the hydrogen bonding equilibria of interest. It is shown that equilibrium constants for hydrogen bonding between neutrals in carbon tetrachloride may serve as K(u)-values, while equilibrium constants for hydrogen bond formation between an anion and a neutral in an aprotic solvent may be converted into a K(u)-value if a K(u)-value for hydrogen bonding between the neutral and the solvent is known. Application of linear free energy relationships for determination of equilibrium constants unavailable in the literature is demonstrated and used extensively. Finally, the consequences of the generally strong hydrogen bonding interaction between acids and polar aprotic solvents for interpretation of measured pK-values in these solvents are discussed. A series of methyl substituted phenols and their anions are used as a general example throughout the paper.