Abstract
Aromatic compounds undergo ionization and generate a molecular ion. This molecular ion is observed in their mass spectra as a prominent peak. For example, in the case of benzene, the molecular ion peak is observed at a mass-to-charge ratio of 78, while in the case of toluene, the molecular ion peak is observed at a mass-to-charge ratio of 92. The benzene molecular ion does not undergo further fragmentation, as enormous energy is required to fragment the benzene ring. Contrastingly, the molecular ion of an alkyl‐substituted benzene undergoes fragmentation and loses a hydrogen atom, producing a benzylic carbocation. The carbocation rearranges to form an aromatic delocalized tropylium cation, which appears in the mass spectra as a strong peak. In the case of toluene, this strong peak is observed at a mass-to-charge ratio of 91.
