Abstract The 1 H-, 13 C- and 15 N-NMR spectra of compounds prepared by coupling benzenediazonium chloride with J-acid, H-acid and Gamma acid under alkaline conditions have been measured. Two-dimensional H,H-COSY, NOESY, H,C-COSY and COLOC spectra and one-dimensional selective INEPT have been used in the assignment of the 1 H- and 13 C-NMR signals. The results show that the above-mentioned aminohydroxynaphthalene-sulfonic acids undergo diazo coupling of benzenediazonium chloride ortho to the hydroxyl groups under alkaline conditions. Using δ( 13 C), δ( 15 N) and 1 J( 15 NH) it has been found that the coupling products exist, in hexadeuteriodimethyl sulfoxide solutions, as equilibrium mixtures of the azo and hydrazone tautomers with strongly prevailing naphthoquinone phenyl-hydrazone configurations.