Indirect Hyperfine Interactions in the Paramagnetic Resonance Spectra of Aromatic Free Radicals

Abstract

It is shown that an electron spin polarization associated with an odd electron in a π‐molecular orbital in an aromatic free radical can, through an atomic exchange coupling mechanism, produce an appreciable resultant electron spin polarization in s‐atomic orbitals at the aromatic protons. This resultant spin polarization gives rise to hyperfine interactions with aromatic protons which are of the same order of magnitude as those observed in the paramagnetic resonance spectra of aromatic free radicals. An equation is developed which relates (proton‐spin)‐(electron‐spin) hyperfine coupling constants to the π distribution of the odd electron in the aromatic free radicals.