The hfi parameters and structure of radical-anions of substituted tetra- and pentafluorobenzenes. Theory and experiment (OD ESR)

Optically detected electron spin resonance (OD ESR) of radical pairs has been employed to take ESR spectra of short-lived radical-anions of substituted fluorobenzenes in liquid non-polar solutions at nearly room temperatures. The quantum-chemical hfi analysis has taken into account possible manifestations of pseudo-Jahn—Teller effects. As shown by comparison with experiment,C₆F₅OCH⁻₃, p-H-C₆F₄OCH⁻₃ and p-(CH₃)₂-C₆F⁻₄ are pseudo-π-radicals with non-planar distortions. A peculiar feature of these radicals is that their structure corresponds to the Jahn—Teller stabilization of excited Π* states. The effect results from a stronger interaction of the Σ* state with Π* than with the ground Π state, because the SOMO space localizations coincide in the Σ* and Π* states.