Heterogeneously Substituted Radicals and Carbenes: Photoelectron Imaging of the FC(H)CN– and FCCN– Anions

Isomer-Dependent Electron Affinities of Fluorophenyl Radicals, •C6H5-xFx (2 ≤ x ≤ 4)

Di-, tri-, and tetrafluorophenyl radicals each have three regioisomers, several of which can form multiple distinct radical structures. We present the photoelectron spectra of the di-, tri-, and tetrafluorophenide regioisomer anions generated from their associated fluorobenzene precursors. By comparing the spectra to the results of density functional theory calculations, we determine that in cases where more than one possible radical isomer is possible for a given regioisomer (radicals formed from 1,2-difluorobenzene, 1,3-difluorobenzene, 1,2,3-trifluorobenzene, and 1,2,4-trifluorobenzene) the most stable anion corresponds to a less stable neutral, suggesting that the reactive C-center on these fluorine-substituted phenyl groups can be controlled by charge state. Full analyses of the spectra and computational results yield further insights into the differences between the electronic and molecular structures of the fluorophenyl radicals and their associated anions.

Trend in the Electron Affinities of Fluorophenyl Radicals ·C6H5-xFx (1 ≤ x ≤ 4)

The electron affinities (EAs) of a series of ·C6H5-xFx (1 ≤ x ≤ 4) fluorophenyl radicals are determined from the photoelectron spectra of their associated fluorophenide anions generated from C6H6-xFx (1 ≤ x ≤ 4) fluorobenzene precursors. The spectra show a near-linear incremental increase in EA of 0.4 eV/x. The spectra exhibit vibrationally unresolved and broad detachment transitions consistent with significant differences in the molecular structures of the anion and neutral radical species. The experimental EAs and broad spectra are consistent with density functional theory calculations on these species. While the anion detachment transitions all involve an electron in a non-bonding orbital, the differences in structure between the neutral and anion are in part due to repulsion between the lone pair on the C-center on which the excess charge is localized and neighboring F atoms. The C6H5-xFx- (2 ≤ x ≤ 4) spectra show features at lower binding energy that appear to be due to constitutional isomers formed in the ion source.