Chemistry of naphthazarin derivatives. 7. Determination of structures of substituted 2,6(7)-dihydroxynaphthazarins by UV and IR spectroscopy

A set of substituted 2,6- and 2,7-dihydroxynaphthazarins were synthesized. The difference in the UV spectra of alkaline alcoholic solutions of 2,6- and 2,7-dihydroxynaphthazarins allows the reliable differentiation of the structures of these compounds. The IR spectra of 2,6- and 2,7-dihydroxynaphthazarins have characteristic nonoverlapping intervals of stretching vibration frequencies of the -hydroxy groups. Based on these spectral regularities, the data on cuculoquinone, which has been isolated previously from lichen Cetraria cucullata and has been identified as 7,7"-bis(3-ethyl-2,5,6,8-tetrahydroxynaphthalene-1,4-dione), were revised and the structure of 6,6"-bis(3-ethyl-2,5,7,8-tetrahydroxynaphthalene-1,4-dione) was assigned to this compound.