Quadrupolar splitting constants

In solution, the quadrupolar coupling constant is not measured directly. Instead, the quadrupolar splitting constant is obtained from relaxation time measurements. The QSC is related to x according to equation 10 ... 

A function closely related to QCC is the Li quadrupolar splitting constant (QSC), defined as QSC = (1 -h/7 /3) x( Li), where r is the asymmetry parameter. The Li QSC values can be estimated from the Li and C(para) spin-lattice relaxation times. The QSC values are correlated with the effects of structure, solvent and temperature on association in solution for aryllithium compounds (155, 171, 172). Conclusions can be drawn about the structure of the associated species in cases where no supporting XRD evidence is available. ... 

TABLE 7. "Li quadrupolar coupling and splitting constants of substituted aryllithium -... 

The conformations of flexible chain molecules incorporated in a nematic environment are investigated. Proton-proton and carbon-carbon dipolar coupling constant measurements are attempted for 1,2-dimethoxyethane and 1,2-diphenoxyethane, in addition to 2H NMR observations of quadrupolar splittings. These conformation-dependent properties are analyzed according to the RIS scheme. Studies are further extended to a mixture of 1,2-diphenoxyethane with a nematic liquid crystal, 4,4 -azoxyanisole. 

A spectrum of perdeuterated potassium laurate in oriented soap-water multilayers (5) is presented in Figure 2. The measured quadrupolar coupling constants are much smaller than those of a static C-D bond, which are about 167 kHz (6) the residual quadrupolar splittings... 

Table 6.1 IS I order parameters as a function of temperature and position in the sn-1 chain of DM PC. The values were calculated from the quadrupolar splittings taken from ref. 100, using a deuteron quadrupolar coupling constant of 167 kHz according to ref. 101...

The analysis of the splitting pattern can afford the isotropic J value and also the value. Furthermore one can consider that the interplay of the quadrupolar, dipolar and indirect coupling also affects the spinning sideband manifolds. Each component of the sextet will have its own effective anisotropy, and, with the same assumption of the perturbation approach, the effective anisotropy evaluated by the analysis of the SSB manifolds affords the ZY value and the value of the quadrupolar coupling constant %. Furthermore, if the Mn-P intemuclear distance is known by X-ray diffraction, the A/ value can be readily extracted [58]. By using the perturbation approach, the interaction of with metal nuclei having spin 5/2 C Mo, Ru) [61,62], 7/2 ( Co) [58] and 9/2 ( Nb) [63] has been investigated. 

Finally, we mention that Li T measurements have been used to study the rate of interconversion between tight and loose ion pairs of lithium fluorenide [44]. The quadrupolar relaxation contribution was derived from Li and Li T data, and a change of the Li quadrupole splitting constant, QSC, obtained via Li quadrupolar and dipolar relaxation rates (see Section 4) with ion pair structure, was indicated. 

It has been long appreciated that a chiral environment may differentiate any physical property of enantiomeric molecules. NMR spectroscopy is a sensitive probe for the occurrence of interactions between chiral molecules [4]. NMR spectra of enantiomers in an achiral medium are identical because enantiotopic groups display the same values of NMR parameters. Enantiodifferentiation of the spectral parameters (chemical shifts, spin-spin coupling constants, relaxation rates) requires the use of a chiral medium, such as CyDs, that converts the mixture of enantiomers into a mixture of diastereomeric complexes. Other types of chiral systems used in NMR spectroscopy include chiral lanthanide chemical shift reagents [61, 62] and chiral liquid crystals [63, 64). These approaches can be combined. For example, CyD as a chiral solvating medium was used for chiral recognition in the analysis of residual quadrupolar splittings in an achiral lyotropic liquid crystal [65]. 

As comparison of Tables 2 and 4 indicates, the changes in volume and entropy at the NI transition obtained for the mainchain dimer and trimer liquid crystals are much larger than those reported for conventional monomer liquid crystals [112]. In Tables 2 and 3, the constant-volume transition entropies (AStr)v are expressed in terms of joules per mole per kelvin. The conformational entropy changes estimated on the basis of the NMR quadrupolar splitting data observed in the LC state are as follows = 13.3... 

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