title: 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.
abstract: 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 log[R(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).
authors.affiliation: Department of Chemistry, University of Turku, FIN-20014 Turku, Finland.
authors.forename: K
authors.initials: K
authors.lastname: Pihlaja
authors.forename: H
authors.initials: H
authors.lastname: Agirbas
authors.forename: P
authors.initials: P
authors.lastname: Valtamo