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, C C + CFO+ → C C O + +F C , 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. © 2007 Published by Elsevier B.V.