Abstract
The normal, iso, and anteiso Δ8- and Δ9-17:1 fatty acid methyl esters were synthesized and their electron impact-induced fragmentation was studied by mass spectrometry. The mass spectra of the preterminal branched monoenoic fatty acid methyl esters present characteristic fragment ions, now understood to be indicative of the position of the methyl group. These fragment ions are in the iso compound m/e 227 [M-55]+, m/e 195 [M-87]+, and m/e 177 [M-105]+, while in the anteiso compound these fragments are shifted by 14 mass units to m/e 213, m/e 181, and m/e 163. The 15-D-iso Δ8- and Δ9-17:1 methyl esters were synthesized because the characteristic fragment ions in the methyl branched compounds indicated a key role of the tertiary hydrogen atom in the rearrangement process. A fragmentation mechanism consisting of a double bond migration triggered by the tertiary hydrogen and an allylic cleavage assuming a displacement mechanism is proposed.
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Boon, J.J., van de Graaf, B., Schuyl, P.J.W. et al. The mass spectrometry of iso and anteiso monoenoic fatty acids. Lipids 12, 717–721 (1977). https://doi.org/10.1007/BF02570901
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DOI: https://doi.org/10.1007/BF02570901