13C NMR and structural study of solid state naphthol-1 and naphthol-2 arylazo-derivatives

Solid state ¹³C NMR spectra of a series of naphthol-1 and naphthol-2-arylazo-derivatives were studied and compared with respective results in solutions. Signals of carbon nuclei of naphthalene ring were assigned. Tautomeric forms of compounds were determined. It was shown that 4-(p-NO₂C₆H₄)-azonaphthol-1 and 1-(p-NO₂C₆H₄)-azonaphthol-2 in solid state existed exclusively in quinohydrazone form. The other two compounds—1-(C₆F₅)-azonaphthol-2 and 2-(p-CH₂C₆H₄)-azonaphthol-1 in solid state were not found in the form of individual tautomeric mixtures but in respective tautomeric equilibrium form. Thus, during transition from liquid to solid state, the tautomeric equilibrium was practically unchanged. In solid state it was found that rotation around aryl-N bond was hindered in the time scale of NMR spectroscopy.