Studies in organic mass spectrometry. Part 23. Role of the aroyl group on the competitive fragmentation reactions of the molecular ion of aroylanilides

The 70 eV and mass-analysed ion kinetic energy (MIKE) spectra of some thiop henecarboxanilides and benzoylanilides (1-10) have been compared in order t o investigate the role of the aroyl (or heteroaroyl) moiety on the abundanc e of the competitive fragmentation reactions occurring in their molecular i ons (amide-bond cleavage and phenol radical ion formation). It has been, sh own that the electron ionisation induced decompositions with high (70 eV) a nd low (MIKE) internal energy excess are qualitatively similar, but remarka ble quantitative differences have been observed that can be accounted for i n terms of the different effectiveness in the transmission of electronic ef fects of substitueuts in the thiophene and benzene rings.