title: Double bond migration to methylidene positions during electron ionization mass spectrometry of branched monounsaturated fatty acid derivatives.
abstract: Electron ionization mass spectra of several monounsaturated methyl-branched fatty acid methyl and trimethylsilyl esters were examined. These spectra exhibited some intensive fragment ions, whose formation could be explained after double-bond migration to methylidene position. This preferential migration (substantiated by deuterium labeling) acts significantly in the case of monounsaturated fatty acid methyl and trimethylsilyl esters possessing a methyl branch localized between the penultimate and the C(4) positions (relative to the ester group), whatever the position of the double-bond. Allylic cleavage and gamma-hydrogen rearrangement of the ionized methylidene group thus formed afforded very interesting fragment ions, which could be particularly useful to determine branching positions of monounsaturated methyl-branched fatty acid methyl and trimethylsilyl esters without additional treatment.
authors.affiliation: Laboratoire de Microbiologie de Géochimie et d'Ecologie Marines (UMR-CNRS 6117), Centre d'Océanologie de Marseille (OSU), Marseille, France. jean-francois.rontani@com.univmed.fr
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Rontani
authors.forename: Nathalie
authors.initials: N
authors.lastname: Zabeti
authors.forename: Claude
authors.initials: C
authors.lastname: Aubert
mesh_terms: D003903:Deuterium / Q000737:chemistry; D004952:Esters / Q000737:chemistry; D005229:Fatty Acids, Monounsaturated / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D007553:Isotope Labeling; D008956:Models, Chemical; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D004952:Esters; D005229:Fatty Acids, Monounsaturated; D006859:Hydrogen; D003903:Deuterium