MECHANISTIC ASPECTS OF CHARGE-REMOTE FRAGMENTATION IN SATURATED AND MONOUNSATURATED FATTY-ACID DERIVATIVES, EVIDENCE FOR HOMOLYTIC CLEAVAGE

The high-energy collision-induced dissociation (CID) of [M + Li](+) io ns of n-butyl ester derivatives of palmitic acid and oleic acid as web as 9,9-H-2(2)-palmitic acid and 11,11-H-2(2)-oleic acid has been stud ied in order to obtain information on the charge-remote fragmentation mechanism of saturated and mono-unsaturated fatty acid ions containing a stable charge centre. The results obtained in the present study ind icate that homolytic cleavage reactions, involving C-H cleavage as an initial rate-determining step, operate during the charge-remote fragme ntation observed for high-energy CID of [M+Li](+) ions of n-butyl palm itate and correspond to a major fragmentation route, With respect to t he charge-remote fragmentation of n-butyl oleate, our H-2-labelling re sults point to the same mechanism, involving an initial C-H cleavage a t allylic positions, for the formations of ions corresponding to a for mal homo-allylic cleavage, and are also consistent with a direct allyl ic C-C cleavage for the formation of ions due to a formal allylic C-C cleavage, These results, however, do not exclude the possibility of ot her minor homolytic fragmentation pathways for the formation of ions i nvolving formal allylic and homo-allylic cleavages.