Pseudorotation as a mechanism for intramolecular electron density transfer. Fragmentation of the octafluoronaphthalene radical anion

• Quantum–chemical calculations were done for octafluoronaphtalene radical anion.
• Potential energy surface of the radical anion has the complicated pseudorotational structure due to π state terms crossing.
• Pseudorotation being the way of the crossing avoidance serves as a mechanism for intramolecular electron density transfer.
• It is the mechanism which determines the CF bond cleavage regioselectivity for the octafluoronaphtalene radical anion.

Adiabatic potential energy surface (PES) of the octafluoronaphthalene radical anion (RA) has been investigated with the B3LYP/6–31 + G* calculations for the gas phase and polar media. In spite of the low symmetry of the RA its PES has been found to be the surface of pseudorotation. The pseudorotation is a way of intramolecular electron density transfer and so played the key role in regioselectivity of the RA fragmentation through the fluoride ion elimination. Transition states for α and β CF bond cleavage in the polar solvent were located. The noticeably lower energy barrier for the β CF bond cleavage explains the observed regioselectivity of the octafluoronaphthalene reductive defluorination.

The work is the first quantum chemical study on regioselectivity of the polyfluoroarene radical anions fragmentation. We have revealed the complicated structure of potential energy surface of the octafluoronaphthalene radical anion and investigated the relation between the surface topography and the radical anion ability to fluoride ion elimination.Figure optionsDownload as PowerPoint slide