Theoretical study of hydrogen-bonded complexes of bromophenols with ammonia: Correlations and predictions of pKa values

COMP 162

Jun Han and Fu-Ming Tao, Department of Chemistry and Biochemistry, California State University, Fullerton, Fullerton, CA 92834
A simple practical method for predicting the acidity constants (as pKa's) of bromophenols is proposed based on density functional theory calculations of a series of hydrogen-bonded complexes of phenol and all congeners of bromophenols, with ammonia as a single probe molecule. Relevant structural parameters and molecular properties of these complexes, primarily involving the acidic hydroxyl group, are examined and plotted against the known pKa values of bromophenols and phenol. Strong linear correlations are found for these compounds. Such correlations are used to determine the pKa values of bromoophenols whose experimental acidities have large uncertainties. Similar predicted pKa values are obtained using different structural parameters and molecular properties of the complexes. The study may be extended to determine the acidities of other halogen-substituted phenols.