Conformational subtlety in large polyphenylene molecules

1,3-Bis(nonaphenyl-3-biphenylyl)benzene (3), a large polyphenylene molecule (C138H94), was prepared by the Diels-Alder addition of 2 equiv. of 1-(pent aphenylphenyl)-2-phenylacetylene to 1,3-bis(3-oxo-2,4,5-triphenylcyclopenta -1,4-dienyl)benzene, and its X-ray structure was determined. The experiment al structures of decaphenylbiphenyl (4) and 3 were compared with calculated structures of these molecules obtained by using methods ranging from molec ular mechanics to hybrid density functional theory. Surprisingly, none of t he computational methods examined correctly predicted the experimentally ob served conformations of both 3 and 4. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.