Deuteron line shape study of molecular order and conformation in the nematogens PAA and MBBA

Dong, Ronald Y.; Tomchuk, E.; Wade, Charles G.; Visintainer, J. J.; Bock, E.

doi:10.1063/1.434486

Cited by 34 publications

(14 citation statements)

References 15 publications

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“…RESULTS The proton decoupled deuteron spectrum at 13.8 MHz and room temperature is shown in figure 1. The appearance of the spectrum is essentially that reported earlier [3] except that in the present case, because of proton decoupling, a better resolution of the individual lines was achieved. The deuteron line, which is a singlet in the isotropic phase, splits roughly into three pairs of lines in the nematic phase.…”

Section: Methodssupporting

confidence: 59%

Deuteron spin-lattice relaxation mechanisms in partially deuterated nematic MBBA

et al. 1978

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The frequency and temperature dependence of the spin-lattice relaxation time, T1, of the various benzene ring deuterons in partially deuterated pmethoxybenzylidene-p-n-butylaniline have been measured. It was found that in the nematic phase the deuteron 7'1 is independent of frequency between 4 and 41 MHz and thermally activated. The results seem to demonstrate that benzene ring rotation is the dominant deuteron relaxation mechanism in the MHz region and that the aniline and benzylidene rings reorient at different rates around the para axes.

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Section: Methodssupporting

confidence: 59%

Deuteron spin-lattice relaxation mechanisms in partially deuterated nematic MBBA

et al. 1978

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“…The best fit is obtained for ~b = 114 ~ + 1.5 ~ (compare data in table). From five independent measurements at the same temperature (T= 28~ the following mean values and standard deviations of the fit for the relevant parameters were found : We consider as the most relevant result of this interpretation that the inclination angle 0 found is significantly smaller than the value 0 = !0 ~ usually assumed in previous studies [12,13]. The value 0 = 3-5 ~ is in agreement with measurements on homologues of MBBA.…”

Section: Interpretation Of the Deuterium-coupled Carbon Spectrum Of Mbbamentioning

confidence: 59%

“…The small splitting observed between the direct-bonded carbon 7 and nitrogen implies that the angle between the C~-N vector and the average molecular axis must be close to the magic angle. This indicates that the average angle between the 1'-7 bond and the molecular axis must be smaller than 10 ~ a number often assumed in liquid crystal studies [12,13].…”

Section: Nitrogen-15 and Carbon-13 Coupled Carbon-13 Resonancementioning

confidence: 96%

“…In this context, we attempt to interpret our data in terms of the torsional angles of the two aromatic rings of the benzylidene-aniline system. Preliminary data based on proton and deuterium spectra have been published by Lee et al [12] and by Dong et al [13]. A complete description of the dynamic molecular structure of liquid crystal molecules is a quite formidable task.…”

Section: Interpretation Of the Deuterium-coupled Carbon Spectrum Of Mbbamentioning

confidence: 97%

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Dipole-coupled carbon-13 spectra, a source of structural information on liquid crystals

Höhener¹,

Müller²,

Ernst³

1979

Molecular Physics

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It is shown that the introduction of well-selected dipolar interactions into carbon-13 spin systems of liquid crystals can lead to well-resolved spectra with a rich content of structural information. Two possibilities are investigated: (a) selective isotope substitution, in particular by deuterium and nitrogen-15, and simultaneous proton decoupling; (b) two-dimensional separated local field carbon-13 spectroscopy. The methods are demonstrated by investigations of benzylidene anilines in their nematic phases. I. INTRODUCTIONIt has been recognized since the early days of nuclear magnetic resonance that the dipolar interactions in oriented media, such as solids and liquid crystals, can provide a wealth of information on molecular structure and on molecular dynamics. Unfortunately, this information is mostly inaccessible by conventional means because of the multitude of interactions leading to broad lines without any noticeable structure. A successful analysis is possible only after drastic simplification of the network of interactions.Numerous techniques have been proposed to simplify N.M.R. spectra of oriented samples. Perhaps the most successful of the presently-known methods is high resolution natural abundance carbon-13 resonance with complete heteronuclear decoupling [1,2]. The remaining anisotropic carbon-13 chemical shifts provide information on molecular structure [3]. However, a quantitative interpretation is often impossible because the calculation of chemical shielding tensors requires complete knowledge of the molecular state functions and this can be an exceedingly demanding task, particularly for complicated molecules or solid systems [4]. The interpretation of chemical shielding tensors is therefore based mostly on empirical rules, similar to those used for the isotropic shifts in solution, rather than on a theoretical analysis. The same situation exists for homonuclear high resolution studies utilizing multipulse schemes [2,5] to suppress the homonuclear dipolar interaction. Again, chemical shielding tensors remain as the only informative quantities.The selective reintroduction of dipolar interactions or the selective removal of dipolar interactions proved to be a very fruitful idea. A sufficiently transparent network of interactions is established leading to well-resolved spectral features and permitting complete analysis and interpretation. In favourable systems, a natural simplicity already exists due to a finite number of localized interactions

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“…The use of deuteron magnetic resonance (DMR) to study the molecular dynamics of liquid crystals has increased during recent years [1][2][3][4][5][6][7]. The method is very specific : DMR spectra of deuterated liquid crystals exhibit well-resolved quadrupolar doublets which characterize the motional averaged orientation of each C-D bond in the molecule.…”

Section: ; 7660mentioning

confidence: 99%

Deuteron magnetic resonance in liquid crystals : the interplay of molecular ordering and conformational changes

Deloche

Charvolin

1980

J. Phyique Lett.

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2014 Un examen des résultats de résonance magnétique des deutérons dans différents systèmes thermotropes remet en question l'interprétation récemment proposée par Bos et Doane suivant laquelle (i) la conformation moléculaire moyenne ne change pas avec la température, même aux transitions de phase, et (ii) les mésophases uniaxiales et biaxiales (Smc) sont respectivement caractérisées par deux et trois paramètres d'ordre. Quelques contre-exemples indiquent que ces points ne sont pas généraux et, dans certains cas, ambigus. Le rôle des changements conformationnels ne peut être négligé. Abstract. 2014 Examination of deuteron magnetic resonance data in different thermotropic systems calls into question the explanation recently proposed by Bos and Doane wherein (i) the average molecular conformation does not change with temperature, even at phase transitions, and (ii) uniaxial and biaxial (Smc) mesophases are characterized by two and three molecular order parameters, respectively. Some counterexamples indicate that these points are not general, and in some cases ambiguities are present in their analysis. The role of conformational changes cannot be neglected.

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Deuteron line shape study of molecular order and conformation in the nematogens PAA and MBBA

Cited by 34 publications

References 15 publications

Deuteron spin-lattice relaxation mechanisms in partially deuterated nematic MBBA

Deuteron spin-lattice relaxation mechanisms in partially deuterated nematic MBBA

Dipole-coupled carbon-13 spectra, a source of structural information on liquid crystals

Deuteron magnetic resonance in liquid crystals : the interplay of molecular ordering and conformational changes

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