Investigation of internal and external potentials acting on benzyl halides dissolved in different nematic solvents

The NMR spectra of C6H5CH2X (X = Cl, Br, I) dissolved in three different nematic liquid crystal solvents were analysed to investigate, using the AP-ELS model, the internal and external potentials acting on the solutes. The nematics [ZLI1132, I35 and a zero electric field gradient mixture (55% ZLI1132:EBBA)] were selected to compare the effects depending on the nature of the solvents on both potentials. The internal potential for the rotation around the exocyclic C-C bond shows minima located at phi = +/-90-degrees (C-X bond lies in a plane perpendicular to the ring) and torsional barrier increasing with the steric hindrance of the halide (from X = Cl to X = I) and with the polarity of the solvent (I35 < the mixture < ZLI1132). Concerning the nature of the interactions responsible for the orientational order to the solutes, the results obtained from the AP method were analysed in a mean field approach testing different hypotheses: it seems that the interaction between the polarizability tensor of the solutes and the electric field squared of the solvents plays a non-negligible role in the orientational mechanism for this kind of compound.