A database for the determination of orientational ordering of nine classes of liquid crystals using carbon-13 chemical shifts

Tong, T.‐H.; Fung, B. M.; Bayle, J. P.

doi:10.1080/026782997209522

Cited by 14 publications

(7 citation statements)

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“…Fortunately, the experimental S ZZ in our MBBA sample can be estimated from the anisotropic contribution Dd = d nem À d iso to the 13 C chemical shifts of phenyl ring carbons using the semi-empirical relationship S ZZ = aDd + b. Using the reported values of the parameters a and b for an MBBA homologous series, 36 the consistent value S ZZ = 0.56 AE 0.01 is obtained for eight inequivalent carbons in the phenyl rings (details of the analysis are included in the ESI †). This value is also well within the reported experimental range.…”

Section: Comparison Of Experimental and Computational Resultsmentioning

confidence: 99%

Experimental strategies for ¹³C–¹⁵N dipolar NMR spectroscopy in liquid crystals at the natural isotopic abundance

Jackalin

Kharkov

Komolkin

et al. 2018

Phys. Chem. Chem. Phys.

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Direct dipolar spin couplings are informative and sensitive probes for a wide range of dynamic processes and structural properties at atomic, molecular and supramolecular levels in liquid crystals and other anisotropic materials. Usually, heteronuclear 13C-1H dipolar couplings in liquid crystals with natural 13C abundance are measured. Recording 13C-15N NMR dipolar spectra in unlabeled materials is challenging because of the unfavorable combination of two rare isotopes. Here we design and compare various experimental strategies to measure short- and long-range heteronuclear 13C-15N dipolar couplings in liquid crystalline samples with high molecular orientational order. New techniques were developed to record 13C and 15N spectra of naturally occurring 13C-15N spin pairs with increased signal intensity and spectral resolution while suppressing the signals of the uncoupled isotopes. Highly resolved 13C-15N dipolar spectra were recorded within an experimental time of a few hours. Coupling constants in a broad range of 10-1000 Hz between spins separated by up to five chemical bonds and distances of up to 5 Å were measured. Because of their relatively low demands on radio-frequency power levels, the experiments were easy to implement using conventional high-resolution solution-state NMR hardware. Experimental data were compared to the results of density functional theory and molecular dynamics computational analyses. The presented experimental methods to characterize the dipolar couplings in unlabeled materials provide novel routes to investigate molecular structure and dynamics in mesophases.

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Section: Comparison Of Experimental and Computational Resultsmentioning

confidence: 99%

Experimental strategies for ¹³C–¹⁵N dipolar NMR spectroscopy in liquid crystals at the natural isotopic abundance

Jackalin

Kharkov

Komolkin

et al. 2018

Phys. Chem. Chem. Phys.

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“…These order parameters can be related to the 13 C chemical shifts through a semi-empirical equation by adopting the established protocols. 33,34 Dd E aS + b…”

Section: Resultsmentioning

confidence: 99%

¹³C NMR investigations and the molecular order of 4-(trans-4′-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT)

Lobo

Kumar

Narasimhaswamy

et al. 2014

Phys. Chem. Chem. Phys.

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The static 1D (13)C and 2D Proton Encoded Local Field (PELF) NMR experiments are carried out in the nematic phase of a less viscous liquid crystal 4-(trans-4'-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT) with a view to find orientational order. The PELF spectra provide better resolution which facilitates the assignment of cyclohexyl and phenyl ring carbons relatively easy. For the cyclohexyl unit, four pairs of dipolar splitting are clearly noticed in contrast to earlier reports on structurally similar mesogens where only two pairs of doublets are seen. The linear relationship between anisotropic chemical shifts and orientational order is established and semi-empirical parameters are obtained to aid the study of the order behaviour of 6CHBT over the entire nematic range. The data further fitted to the Haller equation and a reasonably good agreement is observed. The temperature dependence trends of orientational order parameters extracted for various carbons using (13)C-(1)H dipolar couplings with those of (13)C chemical shifts are compared. A gradual decrease in the order parameter is noticed for different molecular segments while traversing from the core to the aliphatic chain via the cyclohexyl ring. The notable decreasing trends of order parameters along the chain are observed similar to those of the corresponding phenyl cyclohexanes reported earlier.

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“…To study the temperature dependence of the order parameters over a wide temperature range, one can combine the PELF/OMAS results with 13 C chemical shift data, which are readily obtained from one-dimensional NMR experiments. Thus, the 2D PELF/OMAS experiments were performed at four temperatures to obtain the order parameters, which can be related to the 13 C chemical shifts through a semiempirical equation , for the both phenyl rings and C−H bonds in the aliphatic chains: where Δδ = δ LC − δ iso , and a and b are constants. The values of a and b obtained from linear least-squares fitting of the experimental data are listed in Tables and .…”

Section: Resultsmentioning

confidence: 99%

Determination of Long-Range Dipolar Couplings Using Mono-Deuterated Liquid Crystals

and

Fung

2000

J. Phys. Chem. B

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A new approach is presented for the determination of long-range dipolar couplings in liquid crystals. The strategy is the use of monodeuterated compounds to observe 2H−13C splittings in the 13C NMR spectra. As examples, the H−C dipolar coupling constants have been obtained from the spectra of 4‘-cyanobiphenyl 2-deutero- and 6-deuterohexanoate over the whole nematic range. In addition, the 2H NMR spectra of these compounds taken with 1H−H dipolar decoupling show quadrupolar splitting and 1H−H dipolar coupling. Besides the information obtained from the 1D spectra, one-bond and two-bond 1H−13C dipolar coupling constants of 4‘-cyanobiphenyl hexanoate were determined using the method of proton encoded local field (PELF) spectroscopy in combination with off-magic-angle spinning (OMAS). The order parameters were calculated from the 2D spectra, and some of the coupling constants are compared with the H−C coupling constants obtained from the 1D experiments.

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A database for the determination of orientational ordering of nine classes of liquid crystals using carbon-13 chemical shifts

Cited by 14 publications

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Experimental strategies for ¹³C–¹⁵N dipolar NMR spectroscopy in liquid crystals at the natural isotopic abundance

Experimental strategies for ¹³C–¹⁵N dipolar NMR spectroscopy in liquid crystals at the natural isotopic abundance

¹³C NMR investigations and the molecular order of 4-(trans-4′-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT)

Determination of Long-Range Dipolar Couplings Using Mono-Deuterated Liquid Crystals

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A database for the determination of orientational ordering of nine classes of liquid crystals using carbon-13 chemical shifts

Cited by 14 publications

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Experimental strategies for 13C–15N dipolar NMR spectroscopy in liquid crystals at the natural isotopic abundance

Experimental strategies for 13C–15N dipolar NMR spectroscopy in liquid crystals at the natural isotopic abundance

13C NMR investigations and the molecular order of 4-(trans-4′-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT)

Determination of Long-Range Dipolar Couplings Using Mono-Deuterated Liquid Crystals

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Experimental strategies for ¹³C–¹⁵N dipolar NMR spectroscopy in liquid crystals at the natural isotopic abundance

Experimental strategies for ¹³C–¹⁵N dipolar NMR spectroscopy in liquid crystals at the natural isotopic abundance

¹³C NMR investigations and the molecular order of 4-(trans-4′-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT)