Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The ¹H and ¹⁵N_α-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(¹⁵N_α, 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.