Competing 1,3- and 1,2-Hydrogen Shifts in Gaseous Fluoropropyl Cations

An initial 1,2-hydrogen shift versus a 1,3-deuterium shift in emerging FCD2CH2CH2 + ions lead to differing patterns of deuteration in the neutral products that are recovered following reaction with a Brønsted base. Transient dideuterated fluoropropyl ions have been produced in [C3H4D2F+ PhO•] ion−neutral complexes by 70 eV electron impact on FCD2CH2CH2OPh and the resulting fluoropropenes collected in a specially designed electron bombardment flow (EBFlow) reactor. Under these conditions ion−neutral complexes greatly predominate over free fluoropropyl cations. Free ions afford products that are easily distinguished from those that result from ion−neutral complexes, in which the phenoxy radical serves as the Brønsted base. 1,2-Hydrogen shift yields ions containing CH3-groups, while the ions from 1,3-shift have CDH2-groups. Allyl fluoride and 1-fluoropropene arise from ion−neutral complexes, and the extent and positions of deuteration have been determined by 19F NMR. Six deuterated variants of trans-1-fluoropropene can be resolved in the NMR spectrum of the neutral products collected from the EBFlow. The proportions of CH3 and CDH2 measured by integration imply a branching ratio of 1,2-hydrogen versus 1,3-deuterium shift of approximately 94:6.