Deuteron Nuclear Magnetic Resonance in Anthracene Crystals

Nuclear magnetic resonance has been carried out on all nuclei with nonzero magnetic moments present in the alkali ion pairs of deuterated and nondeuterated naphthalene radical anion in 1,2-dimethoxyethane. Both the sign and magnitude of the hyperfine splitting constant (h.f.s.c.) were measured, the alkali h.f.s.c. being studied as a function of the temperature. The Li and Na h.f.s.c. appear to be positive, those of Rb and Cs are negative, whereas that of K changes sign with temperature.The proton and deuterium linewidths were studied as a function of the concentration and were found to vary linearly with the reciprocal of the concentration, pointing to the predominance of the Fermi contact interaction.An analysis of the alkali linewidth is given in terms of the intramolecular relaxation processes. Especially in cases where two isotopes could be studied, i.e. (1H , 2D), (6Li, 7Li) and (85Rb, 87Rb), a quantitative interpretation is presented. . I n t r o d u c t i o nSince the pioneering work o f Atherton and Weissman on the association between sodium and naphthalenide ions [1], many papers have appeared on E.S.R. studies o f ion pairs and much information on alkali metal hyperfine splitting constants (h.f.s.c.) has been collected [2], The alkali metal hyperfine coupling was found to be very sensitive to the solvent and the temperature, suggesting that transfer o f spin density from the aromatic radical to the metal proceeds in a complex manner. Unfortunately E.S.R. experiments only give the absolute value o f the h.f.s.c., whereas in determining the mechanism o f spin transfer the sign o f the h.f.s.c. is also o f importance. D e Boer [3], in an E.S.R. study o f the pyracene anion radical, observed that the Cs and Rb h.f.s.c. exhibited an anomalous temperature dependence. He suggested that the h.f.s.c. o f these ions could be negative as well as positive.Negative alkali spin densities were also proposed by Dodson and Reddoch [4] and Hirota [5], in studying the alkali naphthalene ion pairs. They noticed that regularly decreasing plots o f spin density at the alkali nucleus (calculated as the ratio o f the observed hyperfine splitting in the ion pair to that o f the atom in the gas phase [6]) versus the radius r of the alkali ion, were obtained if the spin density at the Rb and Cs nucleus was taken negative. This correlation between spin density and ionic radius has also been observed for other systems, e.g. alkali anthracenides [5],

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“…For a C -D bond [29] the quadrupole coupling constant (e2qQ/h) is about 0-18 M h z . The linewidths o f the a and /3 2D peaks in the N .M .R .…”

Section: 2 1 1h and 2d Linewidthmentioning

confidence: 99%

N.M.R. investigations on the alkali naphthalene ion pairs

et al. 1971

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“…The deviations from this ideal orientation, which also was observed in anthracene [23], are small (see Table 5). …”

Section: C/ Nqrmentioning

confidence: 75%

On the Nature of the “Bleaching out” Process of the ³⁵Cl NQR Signals in 1,2,3-Trichlorobenzene

Wigand

Weiden

Weiß

1990

Zeitschrift Für Naturforschung A

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“…The experimental errors for the spectral densities might be seen (Figure 3) in the scattering of data measured at the same temperature. We estimated an error of about -+ 5% and k 10% for J,(o) and J2 (20), respectively. Data were found to agree within experimental errors by varying repetition rate between 60 and 150 ms.…”

Section: Dynamics In 60cbmentioning

confidence: 98%

“…By using multi-pulse sequences,2,8 partially relaxed deuterium spectra allow determination of spectral densities of motion J, (o,) and J2 (20,) for various atomic sites in liquid crystals. The site, temperature and frequency dependences of J f ) ( o ) and J9) (20) provide information on the dynamical processes of mesogens.…”

Section: Introductionmentioning

confidence: 99%

Deuterium NMR Study of Molecular Order and Dynamics in 60CB

Dong

O'Bannon

1991

Molecular Crystals and Liquid Crystals

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To test models for molecular reorientation in liquid crystals, the biphenyl core of a perdeuterated nematic liquid crystal, 4-cyano-4'-hexyloxy-d,,-bipheny1-d8 (60CB-dZl) was studied using deuterium NMR spectroscopy. Two overlapped doublets, one from each deuterated phenyl ring, were seen in the deuterium spectrum of 60CB-d,,. An order parameter tensor of the molecular core was used to account for these doublet splittings. The asymmetry parameter q of the electric field gradient was found to be different for the deuterons on the two rings.The spin-lattice relaxation times TI, and TIQ were measured at 15.3 MHz for these rings, using a deconvolution routine that found the areas of two peaks in partially relaxed spectra. Four spectral densities of motion were derived as a function of temperature in the nematic phase. The small step rotational diffusion model or the "third rate anisotropic viscosity" model may be used to account for the measured spectral densities.

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Deuteron Nuclear Magnetic Resonance in Anthracene Crystals

Cited by 69 publications

References 6 publications

N.M.R. investigations on the alkali naphthalene ion pairs

N.M.R. investigations on the alkali naphthalene ion pairs

On the Nature of the “Bleaching out” Process of the ³⁵Cl NQR Signals in 1,2,3-Trichlorobenzene

Deuterium NMR Study of Molecular Order and Dynamics in 60CB

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Deuteron Nuclear Magnetic Resonance in Anthracene Crystals

Cited by 69 publications

References 6 publications

N.M.R. investigations on the alkali naphthalene ion pairs

N.M.R. investigations on the alkali naphthalene ion pairs

On the Nature of the “Bleaching out” Process of the 35Cl NQR Signals in 1,2,3-Trichlorobenzene

Deuterium NMR Study of Molecular Order and Dynamics in 60CB

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On the Nature of the “Bleaching out” Process of the ³⁵Cl NQR Signals in 1,2,3-Trichlorobenzene