An ENDOR study of the radicals in a γ-irradiated single crystal of 17α,21-dihydroxyprogesterone

Single crystals of 17α,21-dihydroxyprogesterone were γ-irradiated at 295 K and studied using X-band ESR and ENDOR. Two types of radical were observed and a structure was assigned to the specimen by analysing the orientational variation of the spectra. The first radical is formed by abstraction of the hydrogen atom from the C(6) carbon while the unpaired electron is delocalized onto the system O(3) C(3) C(4) C(5) C(6). The second radical is formed by attachment of the hydrogen atom to the oxygen O(3) of the carbonyl group, and delocalization of the unpaired electron onto the atoms C(3), C(4) and C(5). The effect of substitution of hydroxyl groups on the hyperfine splitting tensor has been also analysed.