1H and 15N NMR studies of N-substituted-N′-cyanoguanidines

Abstract

A series of N-aryl-N′-cyanoguanidines has been prepared and studied in [²H₆]Me₂SO by ¹H and ¹⁵N NMR spectroscopy. The ¹⁵N NMR coupling patterns for natural abundance and ¹⁵N-enriched guanidines show unequivocally a structure with the CN conjugated with the cyano group. The invariance of δ_H for the nitrogen bound protons with guanidine concentration, the temperature variation, the lack of water-induced change in δ_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.