The structure elucidation of the isomeric mixture of 3-[L-threo-2,3,4-tri -hydroxy-1-(phenyl-hydrazono)butyl] quinoxalin-2(1H)-one in dimethyl sulfoxide solution revisited: experimental and theoretical study

Based on the analyses of 1D and 2D NMR spectra techniques, such as H–H COSY, HSQC, and HMBC of 3-[L-threo-2,3,4-trihydroxy-1-(phenylhydrazono)butyl]- quinoxalin-2(1H)-one in dimethyl sulfoxide solution, it was concluded that this compound exists as a mixture of two isomeric Z- and E- forms I and II rather than the hydrazine imine and diazeny enamine V tautomers reported earlier. The NMR signals assignment was supported using density functional theory.