2-Pyridone, tautomerism investigations

Nitro-2-pyridone exists predominantly in the keto form in DMSO-[Pg.6]

PE spectroscopy offers a method of investigating the tautomeric structure of pyridones and other related compounds in the gas phase by comparison of ionization potentials of the potentially tautomeric compound with those of fixed models. This method is discussed in CHEC 2.04. 

In a review article (91H(32)127) the concept of heterocyclic aromaticity has been presented, summarized, and applied to discussion of tautomerism for a series of hydroxy-substituted azines. Later, the tautomerism of 2(l/7)-pyridone, 2(177)-pyrimidone, 2(177)-pyrazinone, 4-pyrimidone, and 3(277)-pyridazinone in low-temperature inert gas matrices has been investigated by means of IR spectroscopy. It was found that the relative stability of the oxo and hydroxy tautomers of these compounds depends in a systematic way on the relative position of the lactam group and the second nitrogen atom in the ring (92JPC6250). 

The classical problem in the heterocychc series for the hydroxypyridine/pyridone system was discussed in Section 6.5.1.3. In the aliphatic series, the tautomeric equUibria that are mostly investigated are those for malondialdehyde and acety-lacetone, each of them possessing the critical substructure. 

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