13C and 15N NMR study of azo-hydrazone tautomerism in azo dyes containing amino or acetamido groups

Abstract

13C and 15N NMR spectra of ten model azo dyes containing NH2 or NHCOCH3 group in ortho- or para-position to the phenylazo group on benzene, naphthalene and anthracene skeleton were measured. A negligible content of the hydrazone form in these compounds follows from the 13C and 15N chemical shifts and from a slight temperature dependence of the 15N chemical shifts and 1J(15N15N) coupling constants. The 15N isotope effect Δδ (15N) = 0.1 ppm was observed and the values of 1J(15N15N) = 15.6 ± 0.3 Hz were found with compounds double labelled by 15N.