Synthesis and computationally assisted spectroscopic study of tautomerism in 3-(phenyl(2-arylhydrazineylidene)methyl)quinoxalin-2(1H)-ones

Abstract

The recently developed efficient protocol combining implicit and explicit, accurate quantum mechanical modeling of the condensed state [Katsyuba et al., J. Chem. Phys., 2021, 155, 024507] is used to describe the tautomeric/isomeric/conformational composition and the IR and UV-Vis spectra of a series of 3-(phenyl(2-arylhydrazineylidene)methyl)quinoxalin-2(1H)-ones and their solutions in dimethylformamide (DMF) and dichloromethane (DCM). Only Z-isomers of oxo and hydroxy tautomers of the compounds are shown to exist in the solutions in perceptible quantities in conformations stabilized by OH⋯O or NH⋯N and/or NH⋯O intramolecular hydrogen bonds. Oxo tautomers dominate in DMF and in the solid state, while DCM stabilizes hydroxy forms. Convenient condensed-state spectroscopic markers of the tautomers are revealed.