IR and electronic absorption spectra and structures of 3-hydroxy-4-phenylazo-quinoline and 4-hydroxy-3-phenylazoiso-quinoline derivatives

Abstract

It was shown by an analysis of the IR and electronic absorption spectra that 3-hydroxy-4-azophenylquinoline derivatives exist primarily in the azo form in organic solvents, whereas 4-hydroxy-3-phenylazoisoquinoline derivatives exist primarily in the quinone-hydrazone form. The introduction of electron-acceptor groups into the para position of the phenyl ring of 3-hydroxy-4-azophenylquinoline shifts the tautomeric equilibrium to favor the formation of the quinonehydrazone form. It is shown that the band at 550 nm in electronic spectrum of this compound is related to the n →π* transition of the unshared pairs of electrons of the nitrogen atoms of the azo groups.