A variety of free radicals, including primary, secondary, and tertiary alkyls, phenyl, alkoxyl, trialkylsilyl and germyl, and phosphonyl, have been found to add to hexafluorobenzene to form 1-substituted hexafluorocyclohexadienyl radicals. These RC 6F 6· radicals are much more readily detected by EPR spectroscopy than are the corresponding RC 6H 6· radicals because the signals are more resistant to microwave power saturation. An examination of the EPR spectral parameters leads to the conclusion that the six ring carbons in RC 6F 6· radicals all lie in, or close to, a plane except when R is a bulky alkyl group in which case the 1-carbon is out-of-plane and the R group occupies the pseudo-axial position. The RC 6F 6· radicals have UV-visible spectra similar to those of RC 6H 6· radicals. They are not persistent but decay by bimolecular self-reactions at rates that are close to the diffusion-controlled limit. The rate constants for formation of RC 6F 6· for a few R· have been measured and found to be slightly greater than the rate constants for formation of the corresponding RC 6H 6· radicals.
Date de publication
The Journal of Physical Chemistry89, nº 10 (1985) : 1865–1869.