Torsional Barriers and Correlations between Dihedrals in p-Polyphenyls

The torsional energy curves for biphenyl, p -terphenyl, and p -quaterphenyl are calculated using the B3LYP density functional with a triple-ζ polarized basis set. In agreement with recent accurate literature data, barriers of similar height are found at 0° and 90° for biphenyl. For the higher members, the torsional energy curves show an increasing tendency to lower the barrier of the coplanar conformations. The correlation effects between different dihedrals are reasonably small and discussed extensively. In addition, torsional potential functions at different levels of accuracy, suitable for computer simulations, are proposed for all the members of the series up to p -quinquephenyl.