Vicinal-diaryl interactions in stilbenoid hydrocarbons as observed in the through-space charge delocalization of their cation radicals

The conformational preference of vicinal or 1,2-phenyl groups is probed in two classes of ring-substituted 1,2-diphenylbicyclooctene (stilbenoid) hydr ocarbons 1a-1d and 2a-2c. UV-vis spectroscopy reveals, and X-ray crystallog raphy verifies, the intramolecular (edge-to-face) orientation for the pheny l-phenyl interaction in stilbenoids 1a-1d. Most importantly, when two pairs of ortho-methyl substituents are present, the cofacial phenyl groups in th e stilbenoid donors are established by X-ray crystallography and spectrally observed in the cation radicals (2a(+.)-2c(+.)) by the appearance of new b ands with strong absorptions in the near IR with lambda(max) = 1100-1315 nm , analogous to those previously observed in intermolecular (aromatic) inter actions of aromatic cation radicals.