REGULARITIES IN ENERGIES AND GEOMETRIES OF BIARYLS - AN AB-INITIO ELECTRONIC-STRUCTURE STUDY

Results of BLYP/6-311G electronic structure calculations on 29 differ ent conformers/isomers of biaryls possessing the phenyl, naphthyl, and anthryl moieties reveal significant regularities in properties of the se species. Stabilities and geometries of unsubstituted biaryls compos ed of two convex aryl moieties depend mostly on the connectivities of the proximate hydrogen atoms involved in steric repulsions. The comput ed BLYP/6-311G* energies and lengths of the intermoiety C-C bonds in such biaryls are determined within 0.46 kcal/mol and 0.0040 Angstrom, respectively, by the topologies of these connectivities, whereas the a verage intermoiety twist angles are less transferable, the correspondi ng uncertainty amounting to ca. 7 degrees. The observed regularities i n properties of biaryls imply insensitivity of the alpha-electron conj ugation between the aryl moieties to the details of electronic structu res of the entire molecules. Thanks to these regularities, the Z and E conformers of unsubstituted biaryls consisting of two convex aryl moi eties are almost isoenergetic and therefore are expected to be equally populated at ambient temperatures.