Single-crystal ENDOR study of γ-irradiated p-nitrophenol

Abstract

ENDOR measurements at 173 K have been used to measure the hyperfine coupling tensors of four protons in a free radical trapped in γ-irradiated single crystals of p-nitrophenol. Two of the tensors can clearly be identified as belonging to α-protons in a planar π-radical. The angle between the positive dipolar components of the coupling tensors in these two protons, which are expected to lie along the C—H bond directions, is 137°. This results is interpreted as suggesting that the free radical is based on a five-membered ring.