Five-membered ring systems isoindoles

Aromatic systems frequently show prominent molecular ions in electron-impact mass spectra, and isoindoles are no exception. In isoindole itself, the molecular ion is the base peak. The cleavage of the five-membered ring with loss of hydrogen cyanide also generates a prominent ion. Further cleavages, some of which are supported by accurately measured ions,22are shown in Scheme 12. 

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