Spectroscopic studies of isotopically substituted 2-pyridones

The pmr spectrum of 2(1H)-pyridone-¹⁵N provides direct evidence, at low temperatures, of the pyridone form predominating over the hydroxypyridine tautomer by greater than 50:1 in deuteriochloroform solution. The exchange of the enolizable proton appears to be unusually facile under these conditions. Infrared spectra of 2(1H)-pyridone-¹⁵N, 2(1H)-pyridone-1-d, 2(1H)-pyridone-1-d-¹⁵N, 2(1H)-pyridone-¹⁸O, 2(1H)-pyridone-1-d-¹⁸O, 1-methyl-2(1H)-pyridone-¹⁵N, and 1-methyl-2(1H)-pyridone-¹⁸O in solution are reported. Isotopic spectral shifts suggest a revision of previous vibrational assignments and reveal unsuspected anomalous solvent and concentration effects. Implications bearing on molecular structure are discussed.