Tautomeric Equilibria of Substituted 2-Pyridone/2-Hydroxypyridine in the Gas and Aqueous Phases

摘要

Heats of formation, entropies and Gibbs free energies for the twenty structures of substituted 2-pyridone and 2-hydroxypyridine were studied using semiempirical Austin Model (AM1) and Parametric Method 3 (PM3) calculations at the self-consistent field level, both in the gas and liquid phases, with full geometry optimization. It was revealed from the study that 2-hydroxypyridine is predominant in gas phase, while 2-pyridone in the liquid phase which agrees with the experimental and theoretical predictions. All substituents such as F, Cl, OH, CH_(3), NH_(2), NO_(2), CHO, CN, CF_(3) stabilize the 2-pyridone in the gas and liquid phases except F, Cl and NH_(2 )in PM3 calculations in the gas phase. The substituents stabilization is more effective in liquid phase. This was also confirmed by thermodynamic calculations and isodesmic reactions.