Deuterium Quadrupolar Parameters from and 2H NMR Spectra for Pyridine-d5, Benzonitrile-d5 and Chlorobenzene-d 5 Using Liquid Crystal Solvents

The quadrupolar coupling constants (DQCC ) and the asymmetry parameters (rj) for the ortho, meta and para deuterons in pyridine-d5, benzonitrile-d5 and chlorobenzene-d5 were determined by NMR spectroscopy in oriented phases. The 1H and 2H NMR spectra were recorded in the following solutions in liquid crystal solvents: pyridine + pyridine-d5 in PCH , in ZLI 1167 and in EBBA; benzonitrile + benzonitrile-d5 and chlorobenzene + chlorobenzene-d5 in the same solvents. The order parameters of the non-deuterated solutes in the various solutions were calculated using the dipolar couplings o f the proton spectra and the r* structures taken from the literature. The same order parameters were assumed to describe also the orientation of the deuterated solute in the corresponding solutions. Each 2H spectrum yielded three quadrupolar splittings for the three different deuterated positions in the labelled solute. The splittings from the three different solutions of the same solute, together with the order parameters and the ra structure, were used to determine DQCC and rj of the ortho, meta and para deuterons (Pyridine-d5: DQCC ortho= 183(1) kHz, eta ortho = 0.030(5), DQCC meta = 185(1) kHz, eta meta = 0.030(10), DQCC Para = 188(6) kHz, eta Para = 0.01(5). Benzonitrile-d5: DQCC ortho = 171(12) kHz, eta ortho = 0.07(3), DQCC meta = 175(12) kHz, eta meta = 0.05(3), DQCC Para = 176(4) kHz, eta para = 0.10(7). Chlorobenzene-d5: DQCC ortho = 180(2) kHz, eta ortho = 0.06(1), DQCC meta = 174(2) kHz, eta meta = 0.09(3), DQCC Para= 182(4) kHz, eta Para = 0.06(4)). The results are discussed, as well as the limits and possibilities of the method used.