Mechanistic aspects of charge-remote fragmentation in saturated and mono-unsaturated fatty acid derivatives, evidence for homolytic cleavage

The high-energy collision-induced dissociation (CID) of [M + Li](+) ions 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 studied 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 indicate that homolytic cleavage reactions, involving C-H cleavage as an initial rate-determining step, operate during the charge-remote fragmentation observed for high-energy CID of [M+Li](+) ions of n-butyl palmitate and correspond to a major fragmentation route, With respect to the charge-remote fragmentation of n-butyl oleate, our H-2-labelling results point to the same mechanism, involving an initial C-H cleavage at allylic positions, for the formations of ions corresponding to a formal homo-allylic cleavage, and are also consistent with a direct allylic 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 other minor homolytic fragmentation pathways for the formation of ions involving formal allylic and homo-allylic cleavages