Spectres Raman de Résonance de Dérivés Substitués de l'Hydroxyazobenzène en Solution Fortement Acide

Resonance Raman spectra of azobenzene and some hydroxyazobenzene derivatives, in strong acid solution (HCI 6 M), are analysed. All the observed bands between 900 and 1700 cm−1 can be assigned to vibrational modes of the aromatic rings and the azo group, and give evidence for a trans azo type structure both for azobenzene and the para substituted hydroxyazobenzene derivatives studied. Resonance Raman spectra of six substituted 2‐(4′‐ hydroxyphenylazo)‐benzoic acid derivatives in strong acid solutions are investigated. The spectral features are rather different from the above studied hydroxyazobenzene derivatives, but can be explained on the basis of an azo type structure. A strong perturbation effect on the NN stretching mode is demonstrated using deuterium substitution. From the complexity of frequency shifts obtained on deuterium substitution, vibrational coupling between NH bending and many other vibrational modes is evident. A tentative assignment of the observed resonance Raman bands is proposed.