Ion-Molecule Reaction Chemistry of Various Gas-Phase C6H6 Radical Cations

Various gas-phase C6H6 radical cations can be grouped in three general reaction categories depending on their origin. Ionized benzene reacts with 2-propyl iodide to displace an iodine atom and produce C9H13+. The rate constant for this reaction is 1.4 × 10-9 cm3 molecule-1 s-1 at 11 eV of ionizing energy. The major fraction of fragment C6H6 ions from styrene, cyclooctatetraene, anisole, benzaldehyde, phenylhydrazine, and chroman participate in the same reaction. A small proportion of the fragment [C6H6]+. from benzaldehyde, chroman, and phenylhydrazine react with 2-propyl iodide by a second channel to give charge exchange. Ionic decarbonylation of tropone produces [C6H6]+. which reacts with 2-propyl iodide exclusively by the charge exchange channel. These ions constitute a second category for gas-phase C6H6 ions. A third general class of [C6H6]is produced by direct ionization of various acyclic isomers of benzene (1, 5-hexadiyne, 1, 4-hexadiyne, 2, 4-hexadiyne, and 1, 3-hexadien-5-yne). The ions undergo charge exchange with 2-propyl iodide and give no detectable C9H13+. Moreover, these acyclic ions react with their neutral counterparts to produce a rich array of gas-phase products and with 1, 3-butadiene to give C8H7+, C9H9+, and [C10H10]+. This chemistry is not found with ionized benzene or the second category of [C6H6]+. The differences in bimolecular chemistry are attributed to structural and energetic variations for the various C6H6 cations.