Crystal comparison

Amara N, Ratsimba B, Wilhelm A, Delmas H (2004) Growth rate of potash alum crystals comparison of silent and ultrasonic conditions. Utrason Sonochem 11 (1) 17—21... 

Chemical shifts for aromatic azoles are recorded in Tables 17 and 18. Fast tautomerism renders two of the 13C chemical shifts equivalent for the NH derivatives (Table 17a), as in the proton spectra (Table 8a). However, data for the N-methyl derivatives (Table 17b) clearly indicate that the carbon adjacent to a pyridine-type nitrogen shows a chemical shift at lower field than that adjacent to a pyrrole-type TV-methyl group (in contrast to the H chemical shift behaviour). Solid-state studies on imidazole (and pyrazole) show there are three distinct signals for the annular carbon atoms (imidazole C(2), 136.3 C(4), 126.8 C(5), 115.3 ppm). Proton exchange does not occur in the solid, hence the spectra describe the structure in the crystal. Comparison with the corresponding chemical shifts for 1-methylimidazole (137.6, 129.3, 119.7 ppm) implies that tautomerism has been frozen in the solid state <1981CC1207>. Solid-state examination of 2,2/-bis-17/-imidazole also reveals frozen tautomerism. 

Gas/crystal comparisons are as of yet mainly confined to registering structural differences. The interpretation of these results is at a qualitative initial stage. Further investigation of such differences will enhance our understanding of the intermolecular interactions in crystals. 

Uniaxial Single Crystals Comparison with Solution CD... 

As an example. Fig. 3 plots the phonon dispersion curves for three highly S5mimetric directions in the Brillouin zone of the perfect ZnO crystal. Comparison of the theoretical and experimental frequencies shows good agreement for the acoustic branches. The densities of phonon states of the perfect ZnO crystal calculated by integrating over the Brillouin zone are displayed in Fig. 4. Comparison of the results of our calculation and a calcu-... 

As for the polycrystalline-single crystal comparison, in the absence of data concerning the activity of the polycrystaiUne sample at low prenal pressures (10 3 torr), it is rather difficult to conclude regarding the influence of the structure upon the reaction. Nevertheless, this brief comparison between these two series of results emphasizes again the importance of the chemisorption mode of the molecule upon the reaction niechanism, product sdeciivity, and the deactivation of a catalytic surface. 

N. Le Calve, B. Pasquier Z. Ouafik (1997). Chem. Phys., 222, 299-313. Vibrational study by inelastic neutron scattering, infrared adsorption and Raman scattering of potassium, rubidium and cesium dihydrogen arsenate crystals . Comparison with thallium dihydrogen arsenate. 

M. D. Wewers, M. A. Casolaro, and R. G. Crystal. Comparison of alpha-1-antitrypsin levels and antineutrophil elastase capacity of blood and lung in a patient with the alpha-1-antitrypsin phenotype null-null before and during alpha-1-antitrypsin augmentation therapy. Am. Rev. Respir. Dis. 735 539 (1987). 

Geometries were optimized with HF/6-31G for gas phase and with ONIOM (HF/6-31G Dreiding) for crystal. >= Comparison between lines 1 and 2, and 3, and 4, respectively. ... 

Kundu, S., Melton, J.S., Sorensen, D.C., Phillips, G.N. Jr. Dynamics of proteins in crystals comparison of experiment with simple models, Biophys. J. 2002, 83, 723. 

Hulliger, J. Alaga-Bogdanovic, M. Bebie, H. Growth-induced effects of polarity in molecular crystals Comparison of Schottky-and Markov-type models with Monte Carlo simulations. J. Phys. Chem., B 2001. 36. 8504-8512. 

L. Cisse, P. Destruel, S. Archambeau, I. Seguy, P. Jolinat, H. Bock, E. Grelet, Measurement of the exciton diffusion length in discotic columnar liquid crystals comparison between homeotropically oriented and non-oriented samples. Chem. Phys. Lett. 476, 89-91 (2009)... 

H.R. Brand, C. Fradin, P.L. Finn, W. Pesch and RE. Cladis, Electroconvection in nematic liquid crystals comparison between experimental results and the hydrodynamic model, Phys. Lett. A 235(5), 508-514, (1998). 

J. A. Subirana. Elucidation of chain folding in polymer crystals Comparison with proteins. Trends in Pol. Sci., 5(10) 321-326, October 1997. 

Figure 3. Enantiomeric conformations in different crystals. Comparison of the conformations of the H-bonded rings in complexes 3b and c.

There is a fundamental problem. The extent to which X-rays are absorbed as they travel through a crystal depends on the path they take and the mass of the atoms they meet. This therefore affects the diffraction intensities that we measure, and the problem is exacerbated for crystals that have a very anisotropic shape. If the composition of the crystal (the total formula) is known, then the contributions of the atoms of each element can be summed to calculate the absorption coefficient /x (typically quoted in mm ), which represents the amount of radiation absorbed by a crystal of a certain length. Ideally, then, crystals of heavily absorbing compounds should be small and isotropically shaped in order to avoid very different absorptions for different X-ray paths. However, if the three-dimensional geometry of the crystal is known, the absorption can be calculated exactly for the known X-ray path for every reflection, and so the measured diffraction intensity can be corrected. This is called the numerical absorption correction. More often, the crystal dimensions are not known, but the absorption can still be estimated from the total set of measured reflections, as any one reflection can be measured many times using different orientations of the crystal. Comparison of the resulting intensities and fitting to a suitable model then yields the corrections. 

Fig. 246. NiClj-4 HjO single crystal. Comparison of the Fig. 247. NiClj 4H O single crystal. Magnetic phase dia-fitted susceptibility curves to the corresponding experi- gram for H c [74F2]. mental data and the resulting anisotropy [73M25].

P. Yang and K. N. Liou, Light scattering by hexagonal ice crystals comparison of finite-difference time domain and geometric optics models, J. Opt. Soc. Am. A 12 (1995), 162-176. 

Maschio L, Civalleri B, Ugliengo P, Gavezzotd A (2011) Intermolecular interaction energies in molecular crystals comparison and agreement of localized moller-plesset 2, dispersion-corrected density functional, and classical empirical two-body calculations. J Phys Chem A 115 11179... 

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