Effect of phase symmetry on the NMR spectrum of acetonitrile oriented in a uniaxial-biaxial-uniaxial phase

We report here the measurement of the C-H and the H-H dipolar couplings of the methyl group of acetonitrile oriented in the biaxial liquid crystal potassium laurate/1-decanol/water system. These parameters show large variations when measured as a function of temperature. The variations follow the symmetry of the phase as the liquid crystal goes through the sequence of uniaxial - biaxial - uniaxial phases and show a close correspondence to the phase changes that occur in the liquid crystalline solvent coinciding with the onset of biaxiality. The H-C-H bond angle calculated after incorporating vibrational corrections to the dipolar couplings is discussed in terms of contributions in the case of the biaxial liquid crystal arising from vibration rotation interaction effects.(c) 2016 Elsevier B.V. All rights reserved.