Electron ionization mass spectra of 3,4-disubstituted-1,2,4-oxa(thia)diazole-5(4H)-thione(ones). Substituent effects on the mass spectrometric rearrangement of 3-aryl-4-(p-tolyl)-1,2,4-oxadiazole-5(4H)-thiones to the corresponding oxo compounds

✍ Scribed by Kalevi Pihlaja; Hikmet Agirbas; Pauliina Valtamo

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 134 KB
• Volume: 36
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/jms.171

✦ Synopsis

The fragmentation behaviour of ten 3,4-disubstituted 1,2,4-oxadiazole-5(4H)-thiones and seven 3,4-disubstituted 1,2,4-thiadiazole-5(4H)-ones studied here confirmed the earlier observations about the partial rearrangement of the former after ionization into the latter before further fragmentation. In the case of eight 3-(substituted phenyl)-4-(p-tolyl)-1,2,4-oxadiazole-5(4H)-thiones the fragmentations reflecting the above-mentioned molecular ion rearrangement show a clear correlation on the substituent sigma values. The electron-withdrawing substituents destabilize the molecular ion, so higher amounts of the rearranged ion R(1)NCO are obtained. A good correlation of logR(1)NCO against sigma was obtained (r = 0.96). Only a satisfactory correlation prevailed for log(R(1)NCO*/R(1)NCS*) against sigma(r = 0.87).