Fragmentation mechanisms of isoxazole

Fragmentation pathways of isoxazole giving ions C₃H₂ON]⁺, C₂H₃N]^+˙ and C₂H₂N]⁺ are elucidated by means of metastable ion studies and thermodynamic properties. Rearrangement reactions are demonstrated to occur with H and HCO loss. Elimination of carbon monoxide leads to C₂H₃N]^+˙ ions whose reacting configuration is the same as for acetonitrile. All these results can be rationalized in terms of a prior isomerization of isoxazole involving ring opening and 1,2 H migration.