Mass-spectrometric behavior of 2-methyl-3-oxo-3,4-dihydroquinoxaline derivatives

The mass spectra of 20 derivatives of 2-methyl-3-oxo (thioxo)-3,4-dihydroquinoxaline, as well as 2-nitromethylquinoxaline and 2-ethoxycarbonyl-3-oxopiperazine, were recorded in order to study the possibility of detection of a ketimine-enamine equilibrium in the gas phase. It was established that the mass-spectrometric criteria for the identification of the tautomeric forms that were previously proposed for analogous structures are inapplicable in the case of the investigated compounds. The mass spectra of all of the compounds are presented, and correlated schemes for their fragmentation are given.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1118–1121, August, 1981.