Electron paramagnetic resonance spectra of R–C60radicals Part 2: hindered rotation in alkyl- and silyl-C60radicals

Abstract
Photolytically generated alkyl (R) and silyl (SiR3′) radicals react with C60 forming adducts readily identifiable by EPR spectroscopy. The temperature dependence of the spectra of R–C60 radicals indicates a barrier to rotation about the R–C60 bond (ΔH)which varies from ca. 3 kcal mol –1 for CH3–C60 to ca. 7 kcal mol–1 for tert-butyl-C60. Silyl-C60 radicals, on the other hand, are freely rotating about the Si–C60 bond although the Si–R′ bonds are non-rotating on the EPR timescale.