H-1-NMR STUDY ON THE TAUTOMER RATIOS BETWEEN THE HYDRAZONE IMINE AND DIAZENYLENAMINE FORMS IN 3-(ARYLHYDRAZONO)-METHYL-2-OXO-1,2-DIHYDROQUINOXALINES

摘要

The o-substituted 3-(arylhydrazono)methyl-2-oxo-1,2-dihydroquinoxalines 1a-c and 2a,c were synthesized to investigate the tautomeric behavior between the hydrazone imine A and diazenylenamine B forms in a series of mixed dimethyl sulfoxide/trifluoroacetic acid media. The chemical shifts of the hydrazone NH, N-4-H, hydrazone CH, and diazenyl CH protons for o-, m-, and p-substituted 3-(arylhydrazono)methyl-2-oxo-1,2-dihydroquinoxalines 1 and 2 synthesized so far are summarized in Tables 3 and 4, respectively, which are found to be useful for the specification of the proton signals due to the hydrazone imine form A (hydrazone NH, hydrazone CH) and diazenylenamine form B (N-4-H, diazenyl CH). [References: 10]