Unstable intermediates. Part XLV. Hyperfine coupling and spin-polarisation for inorganic and organic radicals

Abstract

In order to facilitate comparison of spin-polarisations in a wide range of π-radicals, a new expression (U^X) is proposed, to replace the familiar Q^X-values. The expression U^X is defined as the ratio of Q^X to the isotropic hyperfine coupling, A^X, calculated for one electron in the appropriate valence s-orbital for atom X. This ratio, which has been used effectively in describing hybridisation in σ-radicals, has been calculated from electron spin resonance results for a wide range of inorganic and organic π-radicals and is found to follow well defined trends. These lead to empirical generalisations which indicate that spin polarisation is dominated by the valence s-electrons, especially those involved in σ-bonding.