Intramolecular hydrogen bond investigations in some Schiff bases using C–C and N–C coupling constants

Five Schiff bases, derived from substituted salicylaldehydes and methylamine, have been investigated by analysis of C–C and N–C coupling constants to check potential of those spectral parameters in intramolecular hydrogen bonds research. Two remaining imines, without OH substituent in position 2, were applied as model compounds for imine structure. The one-bond C–C couplings in aromatic ring provide valuable information about bond orders and correlate with bond lengths obtained by X-ray. The one-bond heteronuclear C–N couplings can be used very easily to distinguish between imine and enamine form of Schiff bases. Additionally the two-bond N–C couplings supply interesting information about geometry of the investigated molecules. q 2003 Elsevier B.V. All rights reserved