The mass spectra of sydnones

The mass spectra of thirty sydnoes have been interpreted; the types investigated include 3‐aryl, 3‐alkyl‐, substituted 3‐alkylsydnones; and bis sydnones. A characteristic fragmentation mode involves initial loss of NO and CO from the molecular ion, but peaks corresponding to alkylcarbonium ions dominate the spectra of 3‐alkylsydnones; a cyclic mechanism is suggested for weak transitions involving loss of sydnone neutral molecule from the molecular ion. A mechanism is proposed for loss of chlorine radical from the molecular ion of 3‐(2,4‐dichlorophenethyl)sydnone. An unusual feature in the mass spectrum of trimethylenebis sydnone is rationalised on the basis of a precursor 1,2,3‐oxadiazole ion. The effect of substituents in the aryl ring on the fragmentation of 3‐arylsydnones is discussed.