MECHANISTIC ASPECTS OF HIGH-ENERGY COLLISION-INDUCED DISSOCIATION IN 1,4-BIS-UNSATURATED FATTY-ACID ESTERS CATIONIZED WITH LITHIUM

The high-energy collision-induced dissociation spectra of the n-propyl linoleate [M + Li](+) ion and its H-2(2)-labelled labelled isotopomer containing the label at the C11 position are reported. As demonstrate d for the C11 allylic position of the mono-unsaturated fatty acid, ole ic acid, the removal of a hydrogen radical at the isolated methylene g roup of the 1,4-bis-unsaturated system is found to be a rate-determini ng initial fragmentation reaction when the [M + Li]+ ion is subjected to high-energy collision-induced dissociation. Furthermore, it is show n that the high-energy collision-induced fragmentation of the linoleat e and the alpha- and gamma-linolenate [M + Li](+) ion can best be rati onalized in terms of preferential homolytic C-H and C-C cleavage react ions at activated positions.