Mass spectral fragmentation of 4-oxo-4H-pyrazole 1-oxides and 1,2-dioxides

The characteristic fragmentation pattern in the mass spectra of 4-oxo-4H-pyrazole 1-oxides and 4-oxo-4H-pyrazole 1,2-dioxides involves scission of the ring into two fragments by cleavage of the nitrogen-nitrogen bond and one of the bonds to the carbonyl carbon. Loss of carbon monoxide or oxygen from the molecular ion is not observed.