Ab initio and 17O NMR studies of the substituent effects on the tautomeric equilibrium in 6-X-1H-2-pyridones

¹⁷O chemical shifts are found to be highly sensitive probes in the study of keto-enol tautomeric equilibria due to the strong sensitivity of these shifts to the coordination of the oxygen atom. The large shielding effect observed, both experimentally and theoretically, for the carbonyl oxygen atom in 2-pyridone suggests that the carbonyl π-electronic system is undergoing a strong conjugation with the formal C3=C4 double bond and/or the nitrogen lone pair. A Cl or NH2 substitution at position 6 of the pyridine ring shifts the tautomeric equilibrium toward the 2-hydroxypyridine form, while a CH3 substitution results in the keto form being predominant, as is the case in the parent compound. © 1992 American Chemical Society.

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Author Julio Cesar Facelli Biostatistics & Bioinformatics, Division of Translational Bi ...