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Charge‐remote and charge‐proximate fragmentation processes in alkali‐cationized fatty acid esters upon high‐energy collisional activation. A new mechanistic proposal
Author(s) -
Claeys Magda,
Nizigiyimana Libérata,
Van den Heuvel Hilde,
Vedernikova Irina,
Haemers Achiel
Publication year - 1998
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/(sici)1096-9888(199807)33:7<631::aid-jms668>3.0.co;2-m
Subject(s) - chemistry , alkali metal , dissociation (chemistry) , fragmentation (computing) , ion , homolysis , inorganic chemistry , photochemistry , electrolyte , organic chemistry , radical , computer science , operating system , electrode
The effect of the metal ion on the high‐energy collision‐induced dissociation (CID) of alkali metal‐cationized n ‐butyl and methyl ester derivatives of palmitic and oleic acid was examined. The results show that the alkali metal ion has a pronounced effect and does not act as a mere ‘spectator’ ion with respect to the fragmentation process. While C–H cleavage is a dominant process for [M+Li] + as well as [M+Na] + precursor ions, C–C cleavage is also significant for the [M+Na] + ions. Homolytic mechanisms involving the formation of a transient biradical cation are proposed which enable us to rationalize in a straightforward manner all product ions formed by both charge‐remote and charge‐proximate fragmentations. The mechanistic proposal is discussed in view of available knowledge on electron impact, CID and related processes. In order to predict how the alkali metal ion could affect the reactivity of the postulated biradical state formed following electronic excitation of the alkali metal‐cationized molecules, quantum chemical calculations were performed on methyl and n ‐butyl acetate as model substances. The decreased spin density at the carbonyl oxygen atom in the biradical state may provide an explanation for the greater tendency towards C–C cleavage reactions of the sodium‐cationized fatty acid esters relative to the corresponding lithium complexes. © 1988 John Wiley & Sons, Ltd.