Position-dependent fragmentation mechanism for radical anions of fluorinated benzoates

• The reactivity of the fluorinated benzoate radical anions towards the fluoride ion loss was theoretically investigated.
• The fragmentation mechanism depends on position of fluorine atom to be eliminated.
• The mutihole PES structure gives rise to multichannel mechanism of radical anion cleavage.
• The results are in line with the experimental regularities of the radical cleavage including the process regioselectivity.

DFT calculations were used to study the potential energy surfaces (PESes) of a full series of fluorinated benzoate radical anions (RAs). The sections of PESes along the C–F bond cleavage coordinates in polar media were built, and the transition states for RA fragmentation with fluoride anion elimination were located. The estimated reaction barrier heights let us interpret the experimental regularities of the RA decay including the process regioselectivity.The fragmentation mechanism was shown to depend on the position of the leaving fluorine atom. When defluorination occurs at an ortho- or meta- position to the CO2− group, the reaction coordinate involves pseudorotation as a way for odd electron density transfer to the breaking C–F bond.Additional gas phase calculations were performed to confirm the pseudorotational architecture of the PESes of polyfluorinated benzoate RAs. The results obtained clearly demonstrated that the multihole PES structure gives rise to the multichannel mechanism of RA cleavage.

Figure optionsDownload as PowerPoint slideThe cleavage path of the defined radical anions includes out-of-plane C–F bond deviation to avoid π and σ terms crossing. When F- eliminates from ortho- or meta- position the path includes pseudorotation to transfer an odd electron density to the breaking bond.