15 N‐NMR‐Studien der Tautomerie in N ‐monosubstituierten Amidinen und in N , N ′‐Diphenylguanidin

15 N NMR Studies of the Tautomeric Equilibrium of N ‐Monosubstituted Amidines and of N , N ′‐Diphenylguanidine 15 N NMR data are reported for tautomeric N ‐monosubstituted amidines 1a and b and for N , N ′‐diphenylguanidine ( 6 ). In order to elucidate the position of the tautomeric equilibrium, the nitrogen resonances of the salts of 1a, b and 6 were also determined. For comparison, chemical shifts δ 15 N were measured of non‐tautomeric amidines 2 – 5 . The preferred tautomers for N ‐phenylbenzamidine ( 1a ) and for 6 have the CN double bond conjugated with the phenyl group. Replacement of an NH proton with an alkyl group, as in 1b , has little effect on the tautomeric equilibrium of amidines.