Kombination von Feldionen- und Elektronestoß-Massenspektren zur Struckturbestimmung,Demonstriert am Beispiel von Monoterpenen

The field ionization and electron impact mass spectra of some monoterpenes are compared. Some general rules applicable also to other substances are derived, summarizing the new structural information that can be obtained by combination of field ionization and electron impact data. The general conclusions are: (1) By comparison of FI and EI mass spectra one can recognize which of the most intense peaks in the EI mass spectra are originating from rearrangement or multistip dissociation processes on the one hand, or from simple direct bond rupture on the other hand. (2) The molecular weight of each substance containing C, H, O, N atoms (or some of them) can be determined unambiguously by field ionization, even if there is no parent peak detectable by electron impact. (3) Extremely strong metastable peaks in the FI mass spectrum are indicative of the splitting off of a polar group from a highly branched carbon atom, under rearrangement of the molecular ion. (4) Ions of about double the molecular weight are often found in the FI mass spectra if the molecule contains carbonyl or hydroxyl groups, or conjugated multiple bonds in aliphatic compounds.