Electron‐impact induced rearrangements in isomeric pyridine aldoximes

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Abstract
The mass spectra of α‐, β‐ and γ‐pyridine aldoximes and the respective O‐methyl ethers were studied. The mass spectral behaviour of α‐pyridine aldoxime is characterized by the elimination of NO, while the molecular ion of the γ‐isomer expels H2 CN. In the case of the β‐isomer the formation of the m/e 67 ion (C4H5N) in a concerted process is the main feature. In the α‐pyridine aldoxime methyl ether, in sharp contrast to the hydroxy analog, the M‐30 peak was found to be due to the elimination of CH2O, the expulsion of NO being absent. The mechanism of the fragmentation reactions is discussed, the conclusion drawn being based on the high resolution measurements as well as on the spectra of the respective deuterioanalogs and on the metastable transitions.