Vibrational analysis by EPR spectroscopy: The ethyl radical

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Abstract
The isotropic 13Cα and proton hyperfine interactions of the ethyl radical have been measured in the temperature range 112–313 K in the liquid solvents propane and 2,2,4‐trimethylpentane. The data are entirely consistent with a value of 500 cm−1 for the out‐of‐plane bending frequency and with the assumption of a harmonic potential well for the vibration. Calculations show that the accuracy of vibrational analysis by EPR spectroscopy is limited by the quality of the experimental data rather than by the assumption of a harmonic potential function. The 13Cα hyperfine splittings for simple alkyls in their ’’planar’’ configuration are calculated to be 37.1 G [⋅CH(CH3)2]; 34.8 G(⋅CH2CH3); 33.1 G (⋅CD3) and 31.9 G (⋅CH3). These results show that hyperfine splittings which are uncorrected for vibrational contributions are not a reliable guide to spin densities.

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