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 differe nt 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 depe nding on the nature of the solvents on both potentials. The internal p otential for the rotation around the exocyclic C-C bond shows minima l ocated at phi = +/-90-degrees (C-X bond lies in a plane perpendicular to the ring) and torsional barrier increasing with the steric hindranc e of the halide (from X = Cl to X = I) and with the polarity of the so lvent (I35 < the mixture < ZLI1132). Concerning the nature of the inte ractions responsible for the orientational order to the solutes, the r esults obtained from the AP method were analysed in a mean field appro ach testing different hypotheses: it seems that the interaction betwee n the polarizability tensor of the solutes and the electric field squa red of the solvents plays a non-negligible role in the orientational m echanism for this kind of compound.