The electron-impact mass spectra of 1,2-benzisoxazole N-oxides

The mass spectra of a new class of heterocyclic N-oxides are reported. It is proposed that the fragmentation processes proceed either by an initial deoxygenation, and or an impact-induced isomerisation, prior to fragmentation. Substituents on the carbocyclic ring normally confer stability on the m olecular ions, whereas those on the heterocyclic ring open up additional fragmentation modes. A phenyl group at the 3-position allows an intramolecular oxygen transfer prior to fragmentation.