ELECTRON-IMPACT MASS-SPECTRAL FRAGMENTATION PATTERNS OF ISOXAZOLINES

Electron-impact mass spectra of 32 isoxazolines, viz. monocyclic, bicy clic and tricyclic isoxazolines are reported. The major fragmentation pattern for the isoxazolines with alkyl, aryl, methoxycarbonyl, (methy lthio)methyl substituents at C-5 is alpha-cleavage while there is a co mpetition between the groups at C-5 for elimination in the case of 5,5 -disubstituted isoxazolines. Bicyclic and tricyclic isoxazolines under go ring fission to afford (isoxazole+allyl radical cation) and (isoxaz ole + cyclopentane radical cation) respectively, to reduce the ring st rain present in the parent isoxazolines. In the case of 5-(2-methylphe nyl)-isoxazolines, the isoxazole cation is observed as the base peak a rising out or CH3 loss followed by H-migration.