Electron paramagnetic resonance spectra of R-C60 radicals. Evidence for RC60C60R dimers

Abstract

Alkyl radicals generated in solution by UV photolysis add to C₆₀ to form adducts of the type RC₆₀, whose EPR spectra are discussed. When R = CCl₃, CBr₃, tert-butyl or 1-adamantyl, the spectrum is sufficiently powerful to permit the detection of several ¹³C satellites associated with the C₆₀ component of the free radical. It is concluded from the intensities and hyperfine interactions of these satellites that ca. 2/3 of the unpaired spin population is located on the three carbon atoms ortho to that bearing the incoming radical R.

There is evidence from the temperature dependence of the EPR spectra of certain RC₆₀ radicals that they exist in equilibrium with their dimer, RC₆₀C₆₀R. For R = isopropyl, tert-butyl, 1-adamantyl and CCl₃, the enthalpy of dissociation is 35.5, 22.0, 21.6 and 17.1 kcal mol^–1 respectively.