Electron-diffraction analysis

The electron diffraction analysis of l,2-bis(methylsulfonyl)ethane, CH3S02CH2CH2S02CH338, yielded a limited amount of structural information. However, this substance has also been studied by X-ray crystallography5, 52, and the two sets of data offer a possibility for comparison. The molecular model is shown in Figure 14. 

The success of the gas phase electron diffraction analysis of cis-and /ra 5-decalin (123) is another example of the use of MM calculations as an auxiliary technique. Minimum energy conformations and vibrational ampUtudes were calculated by both the Lifson and Boyd force fields (30,31) and were used as the starting values for refinement of the geometrical and vibrational parameters for the least-squares analysis. The results revealed no appreciable strain in cj5-decalin (123) other than that expected from gauche interactions. 

Electron diffraction analysis started early in Moscow... 

Zvyagin B.B. (1967) Electron diffraction analysis of clay mineral structures. New-York, Plenum. 

The vapor sample under investigation may not eontain only one kind of speeies. It is desirable to learn as mueh as possible about the vapor composition from independent sources, but here the different experimental conditions need to be taken into account. For this reason, the vapor composition is yet another unknown to be determined in the electron diffraction analysis. Impurities may hinder the analysis in varying degrees depending on their own ability to scatter electrons and on the distribution of their own intemuclear distances. In case of a conformational equilibrium of, say, two conformers of the same molecule may make the analysis more difficult but the results more rewarding at the same time. The analysis of ethane-1,2-dithiol data collected at the temperature of 343 kelvin revealed the presence of 62% of the anti form and 38% of the gauche form as far as the S-C-C-S framework was concerned. The radial distributions calculated for a set of models and the experimental distribution in Figure 6 serve as illustration. 

In addition to the complementary role of these techniques in collecting experimental information, strong and useful interplay is possible in the interpretation of results obtained by these methods. The interrelationship of electron diffraction with mass spectrometry and vibrational spectroscopy is sketched in Fig. 2. This scheme was compiled from the viewpoint of the electron diffraction analysis. Some examples of appUcation will be discussed below. 

Fig. IS. The molecular model of bis(cyclopentadienyl)-titanium boiohydride from an electron diffraction analysis ) as projected in two planes The angles P, and Q are indicated P = 0° and Q = 0° when the apexes of the rings are projected onto the Ti-B bond...

Initial attempts to prepare Cf metal using metallothermic reduction methods (Section II,A) were less than successful due to the high vapor pressure of Cf metal 28, 46). Reduction of californium oxide with La metal (Section II,B) and collection of the product Cf metal on a fused silica fiber (in the apparatus shown schematically in Fig. 15), were found to give metal with usable X-ray diffraction patterns (5). Later, the same method was used to collect Cf metal both on a fused silica fiber for X-ray diffraction analysis and on an electron microscopy grid for electron diffraction analysis 56). As more Cf became available, preparations via this method were carried out on 0.4-1.0-mg samples of californium oxide (55), using fibers of quartz. Be, or C (suitable for direct X-ray diffraction analysis) to collect the product Cf metal. 

Concurrent with our investigation on nitrosamine photochemistry (11), we also initiated an investigation of the ground and excited state chemistry of nitrosamides because of a wide discrepancy in the chemical behavior of these two classes of nitroso compounds. For nitrosamines, the presence of extensive delocalization of the unshared electron pair and the tt electrons of the N=0 group as in VI and VII has been well supported by i) n.m.r. evidence of the restricted rotation about the N-N bond (12), ii) electron diffraction analysis revealing the rather short N-N bond... 

Recently, introduction of amino substituents on the silicon atom resulted in an epoch-making breakthrough in this field, that is, the synthesis of stable silylenes such as 122-125 (Scheme 14.56). ° Although these silylenes are all well characterized by either X-ray crystallographic analysis or electron-diffraction analysis,... 

Electron diffraction analysis for these carbon tubes revealed that the tube wall consists of cylindrically stacked carbon layers. The lattice image for the carbon tubes with a diameter of 30 nm is shown in Figure 10.1.7, where at least four tubes cross each other. The thickness of the walls is about 10 nm, and consequently the carbon has a hollow with a diameter as small as 10 nm. Many small lines, which correspond to 002 lattice planes, are observed in the cross section of the walls for each tube. 

Combined X-ray and electron diffraction analysis led to an orthorhombic unit-cell, with a = 2.468 mn, 1) = 1.152 nm, and c = 1.054 nm. The space group is P2,2,21. Two parallel chains are related, pairwise, by a two-fold screw-axis parallel to the chain axis, and pairs of chains pack in an antiparallel array. The (110) growth planes ol the crystal are parallel to the direction of highest atomic densities. The transformation CTA II cellulose II was discussed. The R factor is 30% with the X-ray diffraction data, and 26% with the electron diffraction data. 

The specific surface areas, Sg, of the carbides were determined chromatographically from the thermal desorption of nitrogen. The phase composition of the samples was checked by X-ray and electron diffraction analyses. X-ray analysis was carried out using an URS-55a X-ray unit with CuKa (Ni-filtered) radiation. Electron diffraction analysis was performed using an EG-100A diffractometer unit. The chemical composition of the carbides samples was determined by chemical analysis. The results obtained are summarized in Table 16.1. 

The organic matrix follows the same pattern. By means of electron diffraction analysis it can be shown that the protein matrix is and remains crystalline and that the structural order of the diffraction pattern is that of a microcrystalline film of gold (Fig. 23)224). It is remarkable that the matrix proteins in other species also produce a single crystal spot pattern. This implies that isolated pieces of organic matrix which are in the order of a few microns thick represent single crystals. Whatever the term single crystal" may mean to the various researchers43, in the context... 

At lower temperatures, molecular AsC12F3 is unstable with respect to the non-molecular substance AsCl AsFg. Complete electron diffraction analysis could not be performed for the whole range of molecules. However, full vibrational spectra were obtained guided by the results for PC1 F5 , the force constants thus extracted showed that the AsC1 F5 have the same structures. This illustrates the point that vibrational spectra can often be obtained in situations where diffraction data cannot. 

Experimental results. Some carbon fibre specimens reveal several orders of 001 particularly in electron diffraction patterns Figure 15 shows a plot of (3 against l2, equation (3), for an electron diffraction pattern from the skin region of a high-modulus material. L(oOl)> usually referred to as Lc, is 3.5 nm and a = 2%. A full description of electron-diffraction analysis in several similarly heterogeneous carbon fibres has been published (23). Figure 15 also includes a plot from the 001 electron diffraction profiles of a carbon whisker, an exceptionally perfect graphite material. This specimen, with an Lc of 10 nm, has zero distortion, and represents the only case where we have found no distortion in a fibrous specimen. 

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