Dimerization in the pyridone/hydroxypyridine tautomeric systems: relative stabilities of the dimers in the 2-pyridone/2-hydroxypyridine and in the 4-pyridone/4-hydroxypyridine systems

Three dimers created from the 2-pyridone/2-hydroxypyridine tautomers and four dimers created by the 4-pyridone/4-hydroxypyridine tautomers were described using ab initio self-consistent-field (SCF) calculation and the energies were corrected for the electron correlation contribution by using the second-order Møller-Plesset (MP2) perturbation treatment. Three and four energy minima were revealed on the dimeric potential hypersurfaces of 2-pyridone/2-hydroxypyridine and 4-pyridone/4-hydroxypyridine, respectively. The relative stabilities of the three- and four-membered systems were evaluated in terms of partition functions constructed from the calculated dimeric parameters. The MP2 energies suggest that, under the conditions of interdimeric equilibrium, there is a coexistence of the oxo-oxo and hydroxy-hydroxy dimers of the 2-pyridone/ 2-hydroxypyridine system. For the 4-pyridone/4-hydroxypyridine tautomeric system MP2 calculations predict a predominance of the hydroxy-hydroxy dimer.