Spin-orbit coupling orthogonality properties

Clear theoretical evidence is presented to show that the u-electron systems of benzenoid aromatic molecules are described well in terms of localized, non-orthogonal, singly-occupied orbitals. The characteristic properties of molecules such as benzene or naphthalene arise from a profoundly quantum mechanical phenomenon, namely the mode of coupling of the electron spins, rather than from any supposed delocalization of the orbitals. Other systems considered include azobenzenes, such as pyridine, five-membered rings, such as furan, and inorganic heterocycles, such as borazine ( inorganic benzene ). 

ESR properties of RSSR cations were reviewed by Bassindale and Hey [1]. Typical g values for the acyclic species with smaller alkyl groups are g, = 2.035, g2 = 2.018, and = 2.003, with = 2.018. The fact that the value of g is close to the free spin value indicates that the cation radicals have relaxed from the orthogonal parent structures to planar structures [1]. The seven line spectrum, which is observed for MeSSMe [1,98] indicates coupling to six equivalent protons, which would not be possible if the radical center were localized on one sulfur. Theoretical calculations indicate a spin population of 0.48 on each S [98]. Other evidence for localization of the unpaired electron in a ti orbital involving both S atoms of disulfide cations comes from an analysis of the anisotropic g tensors and the splittings in symmetrical alkyl disulfides [ 1 ]. 

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