Transfer of F+ versus fluoronium metathesis: Competing reactivities of the gaseous fluoroformyl cation

Reactions of unsaturated hydrocarbons with fluoroformyl cation (CFO+) and of ketene and diketene with CFO+ and CF3+ have been studied in a Flowing Afterglow-Selected Ion Flow Tube (FA-SIFT) in helium at room temperature. Net F+ transfer from CFO+ to the neutral reactants, which is observed in the majority of cases studied, can be explained in terms of formation of a covalent adduct followed by expulsion of CO. Other product ions include the products of net metathesis, CC + CFO+ → CCO + +FC, which are observed in nearly half of the hydrocarbons investigated. Reaction of cyclopentadiene with CFO+ produces inter alia two isomeric C5H5+ ions, neither of which appears to have the same reactivity, as does the C5H5+ ion produced by reaction of propargyl cation (C3H3+) with acetylene. Given that the number of plausible C5H5+ structures is not very great, one of the ions derived from cyclopentadiene is inferred to have the structure of the cyclopentadienyl cation. The reaction of CFO+ with ketene gives F+ transfer, yielding FCH2C≡O+, as the major product channel. By contrast, the reaction of CFO+ with diketene gives no observable F+ transfer. All observed products can be rationalized as coming from initial adduct ions.