Abbaureaktionen mit Elektronen

Abstract

Organic molecules are degradated in the mass spectrometer by electron impact. The degradation reactions proceed stepwise. If the energy content of a molecular ion is sufficient, fragments of low mass are finally obtained. They are usually only of very limited structure specifity. Primary degradation products however often allow the deduction of essential features of the structure. It should therefore be the aim to stop mass spectrometric fragmentation reactions after the first degradation steps. This is possible by recording the spectra of only weakly excited molecules:
The energy need for fragmentation reactions is very different according to the type of component. It is especially low for aliphatic compounds. Their spectra obtained under normal excitation conditions are therefore not characteristic. This can be altered by “individual” treatment of the molecules: If molecules, easily susceptible to degradation, are ionised with electrons of low energy and if at the same time too high thermal excitation of the molecules is avoided, from such compounds too “key fragments” are obtained.