4-Carboxyl-2,6-dinitrophenylazohydroxynaphthalenes tautomerism theoretically re-explained

The tautomeric structures of 4-((2-hydroxynaphthalen-1-yl)diazenyl)-3,5-dinitrobenzoic acid have been revised by using quantum chemical (M06-2X/TZVP) calculations showing that the previously suggested structures are incorrect. By using theoretically predicted relative energies and Uv-Vis spectral analysis of a structurally similar compound (1-((2-nitrophenyl)diazenyl)naphthalen-2-ol), it has been estimated that the tautomeric equilibrium is shifted to the keto tautomer, but not completely.