Mass spectra of some 1,2,4-thiadiazoles

Substituted 1,2,4-thiadiazoles were found to undergo fragmentation by loss of RCN from the molecular ion with both 3- and 5-substituents being involved to some extent. This was followed by loss of sulfur to yield a nitrilium ion. With 5-hydrazino substituents, hydrogen transfer was observed from the substituent to a ring nitrogen atom.