Displacement of Protomeric Equilibria by Self-Association: Hydroxypyridine-Pyridone and Mercaptopyridine-Thiopyridone Isomer Pairs

Article abstract of DOI:10.1021/jo01296a002

Values of both self-association and protomeric equilibrium constants are reported for 2-hydroxypyridine-2-pyridone, 4-hydroxypyridine-4-pyridone, and 2-mercaptopyridine-2-thiopyridone isomer pairs in different solvents.These results provide quantitative evidence for significant differences in the positions of protomeric equilibria for self-associated and monomeric species.The 2-substituted isomers are associated as well-known dimers while the 4-substituted systems form oligomers.In polar and hydrogen-bonding solvents self-association is substantially reduced.Sterically hindered 2- and 4-pyridones are less associated than unhindered systems.The implication of these results, that determinations and interpretations of protomeric equilibrium should take into account the possible dominance of self-association, is discussed.