Protocol for structure determination of unknowns by EI mass spectrometry. II. Diagnostic ions in one ring alicyclic, heterocyclic, and aromatic compounds

Electron ionization (EI) mass spectra of saturated carbocyclic hydrocarbons containing a single ring with three or more members are discussed followed by the examination of their unsaturated analogs, including aromatic hydrocarbons. Mass spectrometry characteristics of heterocyclic compounds for each cycle size with one, two, three, and more hetero-atoms in a ring are considered along with their mono- and polyunsaturated analogs. An effect of the (a) size of a cycle; (b) number, nature, and location of elements in a ring; (c) position and nature of ring substituents; and (d) nature and location of unsaturation on the dissociation is revealed. Characteristic dissociation directions of these compounds and diagnostically important ions in their spectra are identified. Basic dissociation rules for alicyclic, heterocyclic, and aromatic compounds under EI are established for further use in the analysis of complex chemicals containing these structural elements.