1H and 2H NMR spectra of pyridine and pyridine-N-oxide in liquid crystalline phase

Add time:09/03/2019    Source:sciencedirect.com

1H and 2H NMR spectra of pyridine and pyridine-N-oxide in nematic phase have been obtained. Three solvents (EBBA, Phase IV, and ZLI 1132) have successfully been used for pyridine, while only two (EBBA and Phase IV) gave reasonable spectra for pyridine-N-oxide. The values obtained for the deuterium quadrupole coupling constant, DQCC, and the asymmetry parameter, η, for 2H(4) in pyridined5 were 185.7 ± 1.0 kHz and −0.046 ± 0.005, respectively. Vanishing values of η are found for 2H(2) and 2H(3) unless a deviation between the direction of the CH bond determined in gas phase for pyridine and the direction of the principal axis of the field gradient are introduced. By assuming that η is the same for all deuterium nuclei in pyridine (η = −0.046) DQCC are determined to have the value 184.2 ± 1.2 kHz for 2H(2) and 187.3 ± 1.2 kHz for 2H(3). The deviation of the direction of the principal axis of the field gradient and the CH bond was 0.7° for 2H(2) and 0.8° for 2H(3). The values of DQCC obtained for pyridine-N-oxide-d5 are 189.0 ± 4.2, 185.2 ± 1.5, and 186.0 ± 1.2 kHz for 2H(2), 2H(3), and 2H(4), respectively, assuming η = −0.046 ± 0.005.

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