Conformations of Bridged Diphenyls. V. A Nuclear Magnetic Resonance Comparative Study of the Conformations of Identically Substituted Diphenyl Ethers, Sulfides, Methanes, Ketones, Sulfoxides, and Sulfones

Using n.m.r. methods developed in earlier papers, the conformations of two series, one doubly ortho-substituted and one triply ortho-substituted, of six identically substituted bridged diphenyls were compared. The ethers, sulfides, and methanes have been shown to adopt the same conformation in which the di-ortho-substituted ring is perpendicular to the central bridge plane while the other ring lies in that plane and an ortho hydrogen takes up the "inside" or "proximal" position. The benzophenones and sulfoxides prefer a conformation in which the dihedral angle between each ring and the central plane is about 40–50° and an ortho hydrogen adopts the "outside" or "distal" position. The sulfones adopt a conformation in which the two rings are more nearly perpendicular to the central plane.