Collect. Czech. Chem. Commun. 1988, 53, 213-226

Study of the azo-hydrazone tautomeric equilibrium by electronic spectroscopy and quantum chemistry. I. Electronic spectra

Miloš Nepraš, Miloš Titz, Miroslav Nečas, Stanislav Luňák, Jr., Radim Hrdina and Antonín Lyčka

Research Institute of Organic Syntheses, 532 18 Pardubice-Rybitví


The azo-hydrazone tautomeric equilibrium was studied for p-hydroxy and p-amino derivatives of some arylazo compounds. Substantial differences were observed between the spectral patterns in hydrocarbon and alcoholic solutions at normal and low temperatures; these are due to shifts in the azo-hydrazone tautomeric equilibrium, which depends on the nature of the proton donor para substituent, size and topology of the system (aromatic ring fusion patterns), solvent and temperature. The spectral patterns suggest that the proton transfer from the para substituent takes place after dimerization of the molecule.