Abstract
A dramatic change of infrared spectra of 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol is induced in solution by varying the solvent polarity. It is explained by an equilibrium between two tautomers, which vary in relative proportions, but have structures and bond orders nearly insensitive to the nature of the solvent. On account of the additional two basic sites of the molecule with respect to phenylazophenol, other candidates than the usual azo-quinone hydrazone structures are considered. Optical spectrometries support the existence of a zwitterionic form, favoured by polar solvents and in solid films, while the azo tautomer is not detected.
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