Methylene-transfer reactions of benzylium/tropylium ions with neutral toluene studied by means of ion-trap mass spectrometry

The ion–molecule reactions of C7H7+ ions with neutral toluene are investigated in an ion-trap mass spectrometer, which is shown to be suitable instrumentation for kinetic studies, although the absolute rate constant can only be derived with difficulties. The benzylium ions C6H5CH2+ undergo a formal CH2+ transfer with toluene to afford the corresponding xylenium ions, CH3–C6H4–CH2+, whereas the tropylium ions c-C7H7+ do not react. The results for the parent compound C7H7+ are complemented with data for the tert-butyl derivative generated by collision-induced dissociation of the corresponding p-(tert-butyl)benzyl pyridinium ion. For the tert-butyl substituted ion, the benzylium/tropylium dichotomy exists in a similar manner in that reactive and non-reactive fractions are observed, of which the former is assigned to the benzylium structure on the basis of infrared-multiphoton dissociation spectra.