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 analysis of the complicated one-quantum spectrum of the 10-spin molecule biphenyl dissolved in a nematic solvent. An eight-quantum spectrum was analyzed to obtain estimates of all dipolar coupling constants and chemical shifts, which were used as a starting point to solve the one-quantum spectrum, The dipolar couplings from the one-quantum spectrum were used, in combination with those determined in a previous study using different liquid-crystal solvents, to obtain vibrationally corrected geometrical 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.