Torsion sensitivity in NMR of aligned molecules: study on various substituted biphenyls

To estimate the torsion sensitivity of dipolar coupling, biphenylic molecules were chosen as probes due to their relatively simple structure and the surprisingly high ambiguity of the only flexible parameter -the interring torsion angle. Solution structures of 4,4'-dibromobiphenyl and 4,4'-diiodobiphenyl are reported for the first time in two liquid crystals I52 and ZLI 1695. The comparison of NMR structures of various para-substituted biphenyls (Bps), calculated by the additive potential maximum entropy(APME) approach, shows that the small spread of torsion angle values in case of different solvents and para-substituents is in good agreement with theoretical expectations from hybrid density functional theory (DFT) methods. Furthermore, the real structural changes of interring torsion and the prevalence of solvent effects over para-halosubstitution can be correctly revealed from these small fluctuations. Copyright (c) 2007 John Wiley & Sons, Ltd.