DENSITY-FUNCTIONAL STUDY OF INTRINSIC AND ENVIRONMENTAL-EFFECTS IN THE TAUTOMERIC EQUILIBRIUM OF 2-PYRIDONE

The mechanism of oxo/hydroxy tautomerization in 2-pyridone has been investigated by means of a self-consistent density functional/Hartree-Fock (HF) hybrid method with particular attention to the role of solvent effects. The computed structural parameters, reaction heats, and energy barriers are in good agreement with the values obtained from post-HF models. Specific interactions with a single water molecule strongly enhance the reaction rate and shift the equilibrium toward the lactam form, while the effect of bulk solvent is comparatively negligible. Zero point and entropy effects do not modify the above general trends. The interaction between both tautomeric forms and a water molecule has been analyzed by means of the so called natural bond orbital approach.