H-1 AND N-15 NMR-STUDIES OF N-SUBSTITUTED-N'-CYANOGUANIDINES

A series of N-aryl-N'-cyanoguanidines has been prepared and studied in [H-2(6)]Me2SO by H-1 and N-15 NMR spectroscopy. The N-15 NMR coupling patterns for natural abundance-and N-15-enriched guanidines show unequivocally a structure with the C=N conjugated with the cyano group. The invariance of delta(H) for the nitrogen bound protons with guanidine concentration, the temperature variation, the lack of water-induced change in delta(H) the linear free energy relationship (LFER) analysis and coupling patterns, all show that no prototropic tautomerisation is occurring on the NMR timescale. The findings are considered in terms of possible dissociative and non-dissociative mechanisms.