Collect. Czech. Chem. Commun. 1990, 55, 193-201

NMR studies of 1-phenylazo-3-substituted-2-naphthols in solution and in the solid state

Antonín Lyčkaa, Miroslav Nečasa, Josef Jirmana, Jaroslav Strakab and Bohdan Schneiderb

a Research Institute of Organic Syntheses, 532 18 Pardubice-Rybitví
b Institute of Macromolecular Chemistry, Czechoslovak Academy of Sciences, 162 06 Prague


The 1H and 15Nα-enriched 1-phenylazo-3-X-2-naphthols, where X = COOH (I), X = COOCH3 (II), and X = CONHC6H5 (III), have been measured in various solvents. The values of 1J(15Nα, H) and σ(15N) indicate that in CDCl3, C6D6, CCl4, and CD3NO2 solutions the compounds I and III exist practically completely in their hydrazone forms. The hydrazone form is stabilized by the hydrogen bond of COOH or CONH protons to the C(2)=O group. The compound II represents an equilibrium mixture of azo and hydrazone forms, since it cannot form a similar hydrogen bond. Moreover, the 15N NMR spectra of compounds I-III have been measured in solid state by the CP/MAS technique. The results indicate the existence of two conformers differing by the conformation of COOCH3 group in compound II, which is supported by the 13C CP/MAS NMR spectrum of compound II.