Aromaticity and tautomerism. Part II. The 4-pyridone, 2-quinolone, and 1-isoquinolone series

Abstract

Aromatic resonance energies for 4-pyridone and its analogues are similar to those for the 2-pyridone series. For the bicyclic compounds, the differences in aromaticity between the quinolinoid and the quinolonoid forms are significantly less than for the monocyclic derivatives. A new acidity function H–(q) is derived for the deprotonation of methyl quaternary salts to netural heterocyclic methide and imine bases. Quantitative tautomeric ratios are reported for the thioamide–thioimidate equilibrium in an Appendix.