13C-NMR study on the tautomerism of 3-(arylhydrazono)methyl-2-oxo-1,2-dihydroquinoxalines between the hydrazone imine and diazenylenamine forms

The ¹³C-nmr study was carried out for the tautomerism of the 3-(arylhydrazono)methyl-2-oxo-1,2-dihy-droquinoxalines 1a-g and 2a-e between the hydrazone imine A and diazenylenamine B forms, providing the carbon chemical shifts for the tautomers A and B of compounds 1a-g and 2a-e. The comparison of the carbon chemical shifts for the tautomer B of compounds 1d, 1f , and 2b in deuteriodimethyl sulfoxide with those in deuteriotrifluoroacetic acid showed that the C_4a, C₅, and diazenyl carbons were considerably shielded presumably due to the azo N-deuteration in deuteriotrifluoroacetic acid.