Gas-phase ion–molecule reactions in selected cyclohexanes

Abstract

Ion–molecule reactions of cyclohexane, methylcyclohexane and ethylcyclohexane with hydrocarbon cations derived from these cyclohexanes, respectively, have been studied. These ion–molecule reactions take place via various channels including charge transfer, H− transfer, H2− transfer, H3− transfer, hydrocarbon anion transfer, and association with concerted fragmentation. Among these channels, H− transfer is the most prevalent, and for many of the reacting ions, it is the exclusive channel. Most of the reactions proceed in a direct mode, except for the reactions of C4H5+ or C4H7+ with cyclohexane, which in certain channels proceed via the formation of a long-lived collision complex. Some general trends in the reaction rates are observed: smaller reactant ions tend to exhibit faster reaction rates, and odd-electron ions react faster than the even-electron ions. For certain reactant ions, there is evidence of the existence of multiple structural isomers that have different reactivities.