PUB - Publikationen an der Universität Bielefeld

Gaseous benzyl cations (A(+)) react with up to three molecules of benzyl methyl ether (1) generating condensation product ions B+, mit 181, C+, mit 271, and D+ m/z 361, by elimination of methanol during each condensation step. Additional product ions arise from hydride abstraction from ether 1 to generate alpha-methoxybenzyl cations mit 121 and from a degenerate electrophilic substitution by attack of A(+) on the ether-O atom of 1, resulting in a methoxy group transfer and new benzyl cation A(+). The main final product ions correspond to protonated anthracene, mit 179. The mechanisms of these ion/molecule reactions have been studied by Fourier transform-ion cyclotron resonance spectrometry measuring the kinetics of the individual reaction steps, using specifically deuterated reactants A(+) and 1, and by analyzing separately the reactions of isomeric ions B+ generated from suitable precursors. These studies reveal an interesting array of different mechanisms of the ion/molecule reaction within this system. The condensation reaction proceeds by electrophilic aromatic substitution of benzyl cation A(+) on the aromatic ring of ether 1 and specific elimination of methanol from the a complex via benzylbenzyl cations B+. The benzylic ions B+ undergo a second condensation reaction with ether 1 and generate ions C+, which react by a further condensation with ether 1 to create ions D+. Starting from ions B+ the 2-methylbenzhydryl cations B-dip(+) are formed as an additional isomer which is totally unreactive towards ether 1. In addition, protonated 9,10-dihydroanthracene cations B-cycl(+) are formed by an intramolecular aromatic substitution of ions B+. Separate investigations with specifically generated orthobenzylbenzyl cations B-o(+) and protonated 9,10-dihydroanthracene cations B-cycl(+) prove the rapid interconversion of these ions. Ions B-cycl(+) reacts with ether 1 by a multistep reaction within a single collision complex to produce eventually protonated anthracene, a molecule of toluene, and a molecule of methanol. Finally, the degenerate electrophilic substitution by a benzyl cation A(+) at the O atom of ether 1 was studied. (C) 1998 Elsevier Science B.V.