Regularities in Energies and Geometries of Biaryls: An ab Initio Electronic Structure Study

Results of BLYP/6-311G** electronic structure calculations on 29 different conformers/isomers of biaryls possessing the phenyl, naphthyl, and anthryl moieties reveal significant regularities in properties of these species. Stabilities and geometries of unsubstituted biaryls composed of two convex aryl moieties depend mostly on the connectivities of the proximate hydrogen atoms involved in steric repulsions. The computed 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 ?, respectively, by the topologies of these connectivities, whereas the average intermoiety twist angles are less transferable, the corresponding uncertainty amounting to ca. 7°. The observed regularities in properties of biaryls imply insensitivity of the π-electron conjugation between the aryl moieties to the details of electronic structures of the entire molecules. Thanks to these regularities, the Z and E conformers of unsubstituted biaryls consisting of two convex aryl moieties are almost isoenergetic and therefore are expected to be equally populated at ambient temperatures.