Tautomerism of Aromatic Azo-compounds

Recent results on the tautomeric properties of aromatic azo-compounds in neutral and acid solutions are reviewed. The tautomerism of the conjugate acids of azo-compounds (the trans-azonium cations) is discussed, and also the tautomeric equilibria between azo-forms and quinone hydrazones in acid solutions of p-aminoazo-compounds and in neutral solutions of hydroxyazo- and aminoazo-compounds. Available qualitative and quantitative results on the effects of substituents and of the properties of the medium on the position of tautomeric equilibrium are compared. The problem of applying correlation analysis to tautomeric systems is analysed. A list of 179 references is included.