Conformational Analysis of the Biphenyl Moiety of Dimer Liquid Crystals in the Solid State by High-Resolution Solid-State ~(13)C NMR and Ab Initio GIAO-CHF Calculations

摘要

High-resolution ~(13)C NMR spectra of #alpha#, #omega#-bis[(4, 4'-cyanobiphenylyl)oxy]alkanes (CBA-n, n = 7, 9 and 10) were measured in chloroform solution and 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 in relation to those of CBA-7 and CBA-10' which are similar. Therefore, ab initio GIAO-CHF calculations were carried out and an analysis of the conformation of the biphenyl moiety was attempted by comparing the results of the calculations with the measured high-resolution solid-state ~(13)C NMR spectra. Form these results it was concluded that the torsion angle for the biphenyl moiety of CBA-7 and CBA-10 stays at about 40 dreg. For CBA-9 it is suggested that conformers with torsion angles of about 30 dreg and 60 dreg are also present.