Conformational analysis of the biphenyl moiety of dimer liquid crystals inthe solid state by high-resolution solid-state C-13 NMR and ab initio GIAO-CHF calculations

High-resolution C-13 NMR spectra of alpha,omega-bis[(4,4'-cyanobiphenylyl)o xy]alkanes (CBA-n, n = 7, 9 and 10) were measured in chloroform solution an d in the polycrystalline state. The spectra of the samples in solution are essentially the same; in the polycrystalline state, on the other hand, the spectrum of CBA-9 presents some differences in the aromatic carbon region i n relation to those of CBA-7 and CBA-10' which are similar. Therefore, ab i nitio GIAO-CHF calculations were carried out and an analysis of the conform ation of the biphenyl moiety was attempted by comparing the results of the calculations with the measured high-resolution solid-state C-13 NMR spectra . From these results it was concluded that the torsion angle for the biphen yl moiety of CBA-7 and CBA-10 stays at about 40 degrees. For CBA-9 it is su ggested that conformers with torsion angles of about 30 degrees and 60 degr ees are also present. Copyright (C) 1999 John Wiley & Sons, Ltd.