Mechanistic aspects of high-energy collision-induced dissociation proximate to the charge in saturated fatty acidN-butyl esters cationized with lithium. Evidence for hydrogen radical removal

Abstract

The high-energy collision-induced dissociation spectra of [M + Li]+ ions of n-butyl palmitate or heptadecanoate and their labelled isotopomers containing a 2H2-label at the C-2, C-3 and C-4 positions are reported. As is the case for positions remote from the charge, the removal 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 demonstrated that direct C–C cleavage involving γ bonds relative to the carbonyl bond or bonds more remote from the charge may be regarded as a secondary fragmentation route. Direct C–C cleavage of the β bond should, however, be considered as a reaction competitive with C–H cleavage in the formation of the corresponding distonic ions. © 1997 John Wiley & Sons, Ltd.