Charge-remote and charge-proximate fragmentation processes in alkali-cationized fatty acid esters upon high-energy collisional activation. A new mechanistic proposal
✍ Scribed by Claeys, Magda; Nizigiyimana, Libérata; Van den Heuvel, Hilde; Vedernikova, Irina; Haemers, Achiel
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 349 KB
- Volume
- 33
- Category
- Article
- ISSN
- 1076-5174
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✦ Synopsis
The e †ect 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 e †ect and does not act as a mere "spectatorÏ 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 signiÐcant 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 a †ect 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.