The mechanism of spin polarization in aromatic free radicals

The spin-polarization mechanism in aromatic systems is analyzed with refere nce to the prototypical phenoxyl. cyclohexadienyl and benzyl radicals. In p articular, a decomposition into "first-order'' and "second-order" contribut ions is proposed, which helps to rationalize the different nature of the sp in density for atoms in alpha or in beta positions with respect to the radi cal center. The different weights of the two contributions are discussed on the basis of Hartree-Fock and density functional computations.