Electronic structure of π-systems. Studies of electronic structures and tautomeric transformations of a series of 4-methyl-8-(R-phenylazo)dihydrofuro[2,3-h]coumarin-9-ones

Abstract

Tautomeric transformations of a series of 4 methyl 8 (R phenylazo)dihydrofuro[2,3 h] coumarin 9 ones were studied by 1 H NMR, IR, electronic absorption spectroscopy, mass spectrometry, and quantum chemistry methods. The obtained results suggest that (p R phenyl) derivatives exist in the quinone hydrazone form, while (o R phenyl)derivatives exist as a mixture of quinone hydrazone and azo enol tautomers with domination of the former. The anti quinone hydrazone tautomers with a strong intramolecular hydrogen bond are more favorable than the syn quinone hydrazone tautomers.