One Potentially Tautomeric Functional Group

Compounds with One Potentially Tautomeric Functional Group 

The summary of theoretical studies of oxo -hydroxy tautomerism of various heterocycles by AMI, MNDO-PM3, and MNDO semiempirical methods has been published (91JCC17). 

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 prototropic tautomerism of 2-hydroxypyridine (1 2) is frequently considered as a prototype for oxo hydroxy tautomerization processes in heterocycles, which resulted in comprehensive studies of this heterocycle by a wide variety of theoretical and experimental methods. 

The traditional evaluation of tautomeric equilibria by comparison of the pK values of the conjugate acids of the tautomeric system and the fixed-form model compounds has been continued, although spectroscopic and other methods have been used complementary. These estimates are based on assumptions that the cations resulting from protonation and the methylated derivatives all have the common structure. 

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II. Compounds with One Potentially Tautomeric Functional Group. 3... 

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