Spectroscopic studies of keto–enol equilibria. Part XIII. 15N-substituted imines

Schiff bases have been synthesized from [15N]ammonia and 1-hydroxy-2-acetonaphthone, 2-hydroxy-1-naphthaldehyde, 5-methyl- and 4,5-dimethyl-acetophenones, 2-hydroxybenzophenone, benzoylacetone and 2-acetyl-5,5-dimethylcyclohexane-1,3-dione. The 1H n.m.r. and u.v. data permit assignment of tautomeric equilibria. The results indicate that the percentage of amide form is usually greater in these ammonia adducts than in the analogous methylamine or aniline derivatives. Proton–proton spin-coupling measurements provide important information concerning the electronic delocalization in the aromatic rings.