Electron paramagnetic resonance spectra of R–C60 radicals Part 2: hindered rotation in alkyl- and silyl-C60 radicals

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.