Mass spectrometric study of isatins III. Isatin and N-methylisatin ketals

Abstract

In contrast to isatin and N-methylisatin, their ethylene-, propylene-, and 2,3-butyleneketals undergo fragmentation via several pathways. In addition to the principal fragmentation pathway — successive loss by the molecular ion (M+) of a CO group and a dioxolane ring or its fragment, the M+ ions of the ketals are also fragmented with elimination of a dioxolane fragment or the substituent attached to the nitrogen atom and, subsequently, a fragment of the dioxolane ring. The fragmentations of some of the fragment ions were investigated by means of the mass spectra of N-trideuteromethyl analogs.