Comparison of ion-molecule reactions in cyclohexane, methylcyclohexane and ethylcyclohexane

Cyclohexanes including cyclohexane (C$_{6}$H$_{12})$, methylcyclohexane (C$_{7}$H$_{14})$ and ethylcyclohexane (C$_{8}$H$_{16})$ are significant components of many practical fuels. C$_{6}$H$_{12}$ and C$_{7}$H$_{14}$ have been chosen as representative cycloalkanes in several proposed surrogate mixtures for jet fuels. In this study, the gas-phase ion-molecule reactions in these three cyclohexanes are examined, and comparison of the reaction channels in each of the cyclohexanes are made. A variety of reaction channels has been observed, which include charge transfer, H$^{-}$ transfer, H$_{2}^{-}$ transfer, H$_{3}^{-}$ transfer, hydrocarbon anion transfer, and association with concerted fragmentation. Among these channels, H$^{-}$ transfer is the most prevalent in the three cyclohexanes and, for many reactant ions, is the exclusive channel. Also observed is that H$_{3}^{-}$ transfer occurs only in C$_{6}$H$_{12}$ while C$_{3}$H$_{7}^{-}$ transfer occurs only in C$_{8}$H$_{16}$.