Fragmentation reactions of alkylphenylammonium ions

The fragmentation reactions of a variety of alkylphenylammonium ions, C6H5N H3-nRan+ (n greater than or equal to 1, R = CH3, C2H5, i-C3H7, n-C4H9) were studied by energy-resolved mass spectrometry. Ionization was by fast atom bombardment (FAB) or electrospray ionization. Energy-resolved fragmentation data were obtained by low-energy collision-induced dissociation (CID) in t he quadrupole cell of a hybrid sector/quadrupole instrument following FAB i onization and by cone-voltage CID in the interface region of the electrospr ay/quadrupole instrument. A comparison of the two methods of obtaining ener gy-resolved data showed that very similar results are obtained by the two m ethods. The fragmentation reactions of the alkylphenylammonium ions are rat ionalized in terms of competitive formation of an [R+ -NC6H5H3-nRn-1] compl ex or a [C6H5H3-nRn-1N+. - R-.] complex. The former complex fragments by in ternal proton transfer to yield C6H5H3-nRn-1NH+ and [R - H] whereas the lat ter complex fragments to form C6H5H3-nRn-1N+ and an alkyl radical. Alkane e limination, which is very prominent for tetraalkylammonium ions, most likel y involves sequential elimination of an alkyl radical and either an H atom or an alkyl radical for the phenyl-substituted ammonium ions. Copyright (C) 1999 John Wiley & Sons, Ltd.