Determination of the stabilization energy of the cyclopropylmethyl radical by EPR spectroscopy

Cyclopropylmethyl radicals were generated from cyclopropylmethyl bromide and studied at low temperatures by EPR spectroscopy. From the exchange broadening in the spectra the internal rotation barrier about the C‐β‐C‐α^. bond was found to be 11.5±0.8 kJ mol⁻¹. Hence, the stabilization energy of the cyclopropylmethyl radical is 10±2.3 kJ mol⁻¹ and DH^° (cyclopropylmethyl‐H) = 400 kJ mol⁻¹. The radical's structure, conformation and C‐β‐C‐α^. rotation barrier were calculated by the semi‐empirical MNDO‐UHF method.