MECHANISTIC ASPECTS OF HIGH-ENERGY COLLISION-INDUCED DISSOCIATION PROXIMATE TO THE CHARGE IN SATURATED FATTY-ACID N-BUTYL ESTERS CATIONIZEDWITH LITHIUM - EVIDENCE FOR HYDROGEN RADICAL REMOVAL

The high-energy collision-induced dissociation spectra of [M+Li](+) io ns of n-butyl palmitate or heptadecanoate and their labelled isotopome rs containing a H-2(2)-label at the C-2, C-3 and C-4 positions are rep orted, As is the case for positions remote from the charge, the remova l of a hydrogen radical at proximate positions has been found to be an initial and decisive fragmentation reaction when [M + Li](+) ions are subjected to high-energy collision-induced dissociation, It is also d emonstrated that direct C-C cleavage involving gamma bonds relative to the carbonyl bond or bonds more remote from the charge may be regarde d as a secondary fragmentation route, Direct C-C cleavage of the beta bond should, however, be considered as a reaction competitive with C-H cleavage in the formation of the corresponding distonic ions. (C) 199 7 John Wiley & Sons, Ltd.