Comparisom of electron impact and field desorption mass spectra I : Substituted sultams

The low and the high resolution electron impact (EI) and field desorption (FD) mass spectra (MS) of substituted 5- or 6-membered ring sultams are given and the main fragmentation pathways are interpreted. Sultams carrying polar substituents, such as dicarboxylic acids and their mono- and di-amides show either small or no molecular ions with EI-MS. Their existence, however, can be indirectly inferred by metastable defocusing. In contrast to these findings FD-MS display in all our examples the quasimolecular ions (M + 1)⁺ as the base peaks of the spectra. While the pattern for the EI fragmentations follows the generally known rules very closely, five general aspects for the fragmentation pathway of FD mass spectra have been established which demonstrate the characteristics of this modern analytical method. The use of high temperature activated emitters enables a choice to be made between obtaining only molecular peaks and producing significant fragments via a controlled thermal degradation. This is the first time that the complementary and different characters of the information obtained with the two ionization modes EI and FD have been demonstrated on a homologous series of compounds.