A reinvestigation of the collisional activation mass spectra of [C7H7]+ ion mixtures

Abstract

AbstractThe collisional activation (CA) mass spectra of the two isomeric [C7H7]+ ions, benzyl and tropyl, have been reassessed. The structure‐characteristic feature of their CA mass spectra, the m/z 77:74 abundance ratio, has been confirmed as 3.15 ± 0.2 for benzyl cations and lowered to 035 ± 03 for tropyl ions. Benzyl–tropyl cation mixture analyses were made and were in general agreement with earlier CA results, but still disagree with the results of ion cyclotron resonance experiments. The behavior of toluene molecular ions close to their dissociation threshold to [C7H7]+ + H˙ was examined; for metastable [C7H8]+˙ ions an approximately 55:45 benzyl:tropyl ratio was found. Observations are discussed in relation to photoionization and photoelecrron‐photoionization coincidence studies, both of which predict high tropyl ion contents at low energies. However, at the lowest energies attainable in this study the benzyl content failed to fall below 50% and it is concluded that toluene molecular ions do not generate tropyl cations at their dissociation limit.