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Protonation Studies of Schiff Bases Using 13C and 15N-NMR Spectroscopy
* 1 , 1 , 1 , 2 , 2 , 3
1  Dpto. de Química Orgánica y Bio-Orgánica, Fac. de Ciencias, UNED, 28040 Madrid, Spain
2  Dpto. de Química Inorgánica, Fac. de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain
3  Instituto de Química Médica, CSIC, Juan de la Cierva 3, 28006 Madrid, Spain

Abstract: 13C and 15N-NMR spectroscopy provides clear evidence that the Schiff bases of 3-hydroxy-4-pyridinecarboxaldehyde exist as a mixture of hydroxyimino and oxoenamino tautomers in acid media. The study of the stabilities of the tautomeric forms has been approached using density functional calculations (B3LYP/6-31G**). The X-ray molecular structure of (E)-4-[(4-bromophenylimino)methyl]-3- hydroxypyridinium tetrafluoroborate has been solved.
Keywords: Schiff bases, Tautomerism, Hydrogen bonds, NMR spectroscopy, Density functional calculations, X-ray