A MULTIPLE-QUANTUM H-1-NMR STUDY OF CONFORMATIONAL BIASING OF BIPHENYL IN A NEMATIC LIQUID-CRYSTAL

Multiple-quantum H-1 NMR spectroscopy was used to simplify the analysi s of the complicated one-quantum spectrum of the 10-spin molecule biph enyl dissolved in a nematic solvent. An eight-quantum spectrum was ana lyzed to obtain estimates of all dipolar coupling constants and chemic al shifts, which were used as a starting point to solve the one-quantu m spectrum, The dipolar couplings from the one-quantum spectrum were u sed, in combination with those determined in a previous study using di fferent liquid-crystal solvents, to obtain vibrationally corrected geo metrical parameters and orientational order parameters, The effective internal rotational potential was found to be shifted slightly toward a more planar configuration relative to the gas-phase potential, with an equilibrium dihedral angle of 37 degrees. (C) 1996 Academic Press, Inc.