Fluoropropyl cations

A couple of significant examples of the use of halide transfer reactions for the investigation of reaction mechanisms and of the structure of gaseous cations, the second field of application of these processes, are given below. More examples are reported in Section II.B. The first example concerns the reaction of the 2-fluoropropyl cation (1) with its neutral precursor /-butyl fluoride to yield the /-butyl cation, a reaction which could proceed either via F abstraction or via H+ transfer and HF elimination, both routes being exothermic (Scheme l)6. Collection of the neutral products by means of the EBFlow... 

Shifts of different atoms/groups to the same cationic center provide a measure of relative propensities to migrate. Three ion-neutral complexes form from the molecular ion drawn in Scheme 15. The EBFlow experiment required two isotopic labels (the asterisk designates C) in order to tease apart the different pathways (including about 10% of the molecular ions that eliminate PhOD " " via yw-elimination to yield undeuterated 2-fiuoropro-pene). Product analysis was rendered more difficult because the two 1-fluoropropyl cations CFI3CH2CHF and CH3CHCH2F have nearly the... 

A striking feature of this EBFlow radiolysis experiment is the low yield of 2-fluoropropene, all of which can be accounted for by the small amount of free fluoropropyl ions generated by 70 eV electron impact. This result implies that the skeletal rearrangement of linear to branched fluoropropyl cations (which gives rise to the neutral products in equation 21, for example) occurs too slowly to take place in the brief lifetime of ion-neutral complexes. In this regard the ion-neutral complexes formed by ionizing... 

According to the rules of orbital symmetry, vicinal hydride shift in cations is a thermally allowed suprafacial 1,2-sigmatropic shift. Migration of a more distant hydrogen can occur by successive 1,2-shifts, via a bridged structure (such as the cyclooctyl cation in Scheme 7 ), or by corner-to-corner transfer in a protonated cyclopropane (which give net 1,3-shifts). An EBFlow experiment has been able to measure the competition between 1,2- and 1,3-shift in the 1-fluoropropyl system. 

---