Gas phase rearrangement of benzyl, tropylium cations has been one of the most widely studied reactions in mass spectrometry. Published literatures concluded that electron-impact ionization of toluene and related compounds generated tropylium ion by which all of the seven carbon atoms became indistinguishable from each other. This also led to the assumption that all hydrogen atoms in the toluene molecule tend to lose identity in the process. Deuterium isotope experiments were used to support their finding. However, these mass spectral experiments were performed using low resolution mass spectrometers, creating a chance for wrong interpretation for deuterium scrambling. For example, low resolution mass spectral data cannot differentiate between C7H5D2/C7H3D3 (93 m/z) and C5H5/C5HD2 (65 m/z) on the other hand, accurate mass spectra can eastly identify the differences. Additionally, mass spectra experiments were performed on full scan MS, where all the fragments were resulted in one run. To test this assumption further, we used MSMS GCQTOF to study fragmentation of toluene and halotoluenes as well as their deuterium labeled compounds. We selected and filtered individual ions and monitor their fragmentations at different collision induced dissociation (CID) by MSMS. Our results showed that deuterium scrambling does not take place during the conversion of toluene molecular ions (containing different number of deuterium atoms) and were able to identify all the precursors and product ions for each type of fragmentation. Contradicting earlier literature, molecular ions (radical cations) were found to only lose either hydrogen or halogen radical to produce tropylium cation, but loss of acetylene molecule (C2H2) only took place from the tropylium ion not from the molecular radical cation to form the product C5H5 or its analogs following by a loss of another acetylene molecule to form C3H3 or analogs. Detailed experimental results will be presented.

Gas phase benzyl, tropylium cations rearrangement reinvestigated using accurate mass quadrupole time of flight gas chromatography mass spectrometry (GCQTOF)

255th National Meeting (2018)

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