Mass spectral fragmentations of ionized alkylperhydro‐1,3‐oxazines

The mass spectral fragmentations of perhydro‐1,3‐oxazine and twelve of its alkyl derivatives were studied by metastable‐ion analysis and exact mass measurement. The role of the nitrogen atom was dominant in these fragmentations. Almost all the primary decompositions of the molecular ions started as α‐cleavage reactions with respect to the nitrogen atom, leading to the loss of a substituent from an adjacent carbon or to a ring‐cleavage reaction. Preference for the ring‐cleavage reaction was increased by a substituent at position 2. Some rearrangement reactions were observed as well. The expulsion of C 2 H 3 O˙ from the molecular ion was particularly favoured for the 3‐methyl substituted compounds. In this elimination, ring carbons 5 and 6 were lost simultaneously with a hydrogen atom transfer to the nitrogen atom.