Substituents Effects on the Azo-Hydrazone Tautomerism of 4-Arylazo-2,6-di-t-butylphenols

Abstract The substituents effects on the azo-hydrazone tautomerism of 4-arylazo-2,6-di-t-butylphenols in carbon tetrachloride were studied by means of infrared and visible spectra. The substituents effects on their absorption spectra were discussed. The azo tautomers are predominant in the tautomeric equilibria of 3′- and 4′-substituted derivatives. Considerable participations of the hydrazone tautomers are found in the equilibria of the 2′-substituted derivatives having substituents capable of forming intramolecular hydrogen bonding with hydrazone-hydrogen atom. In the equilibria of 2′,6′-disubstituted derivatives, the positions of the equilibria move some what to the azo side from those of the corresponding 2′-substituted derivatives.