Ammonia Chemical Ionization Mass Spectra of Sydnones

The mass spectra of twenty-nine sydnones were measured by using NII₃ as a reagent gas. The M + H + NH₃]⁺ ions are the base peaks for the entire series. Very few fragment ions were observed except for the derivatives of 4-hydroxymethylenesydnones (XXI-XXIX). Only the relatively stable sydnonyl-methylene cations are formed. With consistent formation of M + 18]⁺ ion as the base peaks with simple spectra, the NH₃ CI-MS can be an excellent method for the molecular weight determination.