Infrared Spectra of Some Substituted Monoazobenzenes,Hydroxyhydrazone Tautomerism in Orthohydroxy,and Orthoaminoazobenzenes

Abstract

The infrared spectra of substituted monoazobenzenes (O-Cl, m-Cl,p-Cl,p-Br, 2,5-dichloro, O-NO₂, m-NO₂,p-NO₂, and 2,4-dinitro) derived from p-hydroxy, O-aminobenzenes (series A), and of the substituted monoazobenzenes (O-Cl, m-Cl,p-Cl, 2,5-dichloro, p-Br, and O-NO₂) derived from p-amino, O-hydroxybenzene (series B) have been recorded and tentatively assigned. In series A the O-NO₂, m-NO₂, and 2,4-dinitro compounds and all members of series B show a relatively intense IR band at 1651 ± 17 cm⁻¹. The appearance of this band in the nitrocompounds of series A at 1654 ± 14 cm⁻¹ is interpreted as being probably due to coupling of ΔNH₂ and α as NO₂. The band at 1642 ± 8 cm⁻¹ in series B is tentatively as signed as a ν C=O absorption. This interpretation is regarded as evidence of tautomeric equilibrium in series B of these azodyes.