Direct evidence for the existence and the relative stability of gaseous ethylenebenzenium ions from a 13C-labeling study

Direct evidence is reported for the existence of unsubstituted ethylenebenzenium ions in the gas phase, based on 13C-labeling of a methylene position in the precursor β-phenylethyl alcohol or chloride. The 13C location in the products of the substitution reaction induced by gaseous cations in the presence of methanol is consistent with the occurrence of ethylenebenzenium ions 3 which do not display a facile isomerization to benzylic ions 6. The fate of the 13C label in the reaction has been established by the mass spectrometric analysis of the products. It has been verified further by NMR spectrometry, applied for the first time to the analysis of an ion-molecule product from a gas-phase radiolytic study. 15 refs., 2 figs., 2 tabs