Molecular structures of some hydroxyazo compounds and their derivatives

The IR-absorption spectra of 14 sigma-hydroxyazophenyl derivatives with increasing number of fused benzene rings of the aryl moiety are studied in solid stare, in CCl4 solution and in nujol mull. The IR-spectral bands are assigned indicate that these compounds exist in two tautomer forms. The OH group of the aryl moiety to the azo groups is responsible for the hydrazone structure. If solutions in CCl4 are exposed to sunlight the strongly coloured compounds undergo a rapid bleaching, leading to a destruction of the azo group accompanied by an increase of hydrazone structures.