Mass spectrometry of 1,3,4-thiadiazolo thiacrown ethers

The mass spectra of two homologous series of 1,3,4-thiadiazolo thiacrown ethers possessing one or two heterocyclic subunits, respectively, have been correlated and compared with those of closely related open-chain analogues. The prevailing feature in the spectra of these macrocycles is the presence of homologous series of ions, which formally correspond to the sequential loss of C₂H₄O units from appropriate precursors. The majority of these ions have been rationalized in terms of structure and mechanism of formation by assuming an electron impact induced isomerization process (via H migration) of the molecular ion to several competing linear structures prior to fragmentation. Metastable peak analysis and high-resolution measurements provide support for the postulated fragmentation mechanisms and product ion structures.