The 15N and 13C solid state NMR study of intramolecular hydrogen bond in some Schiff bases

In present work set of eight Schiff bases derived from substituted salicylaldehydes and aliphatic and aromatic amines has been studied in the solid state by 15N and 13C CPMAS NMR methods. 15N CPMAS NMR measurement is especially useful for investigation of the tautomerism in the compounds considered, owing to the large difference in the nitrogen chemical shifts of OH and NH tautomers. In the solid state, four of the compounds examined were shown by 15N CPMAS NMR to exist as OH tautomeric forms, and the remaining four as the corresponding NH forms with different stage of proton transfer process, from oxygen to nitrogen site. This was confirmed by 13C CPMAS. The results reported were compared with those obtained for only two compounds in CDCl3 solutions (solubility problems). q 2004 Elsevier B.V. All rights reserved.