Tautomerism of 5-hydroxy-1,4-naphthoquinone-4-imines

The existence of tautomeric equilibrium in solutions of 5-hydroxy-1,4-naphthoquinone-4-imines between the p-quinoid and ana-quinoid forms was proven by electronic, PMR and NMR (¹⁴N) spectroscopy. It was found that replacement of the aryl group at the nitrogen atom of the imino group by an alkyl group, and also proton-donor solvents forming hydrogen bonds with the oxygen attached at the C₅ atom cause a shift of the tautomeric equilibrium in the direction of the ana-quinoid form.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2572–2576, November, 1989.