Polarization effects on the tautomeric equilibria of 2- and 4-hydroxypyridine in aqueous and organic solution

The role of electronic polarization effects on the tautomeric equilibria of 2- and 4-hydroxypyridine has been examined through Monte Carlo simulations using a combined quantum mechanical and molecular mechanical (QM/MM) potential. The results indicate that differential polarization in the hydroxy and oxo forms contributes significantly to the overall observed solvent effects on the tautomeric equilibria, amounting to 14%-68% of the total free energy of solvation in chloroform and in water. This is accompanied by concomitant changes in molecular dipole moment. Detailed insights into the structural and energetic nature of the solvent polarization effects are presented.