Projections of structure

FIGURE 1.41 The crystal structure of rutile, T102. (a) Unit cell, (b) parts of two chains of linked [TiOe] octahedra, and (c) projection of structure on base... 

Figure 4- Projection of structure of the a-dex-irin-h complex, (C H O h, 4H2O. Cage...

FIG. 19.3. (a) Chain of P atoms in BaPa (b) projection of structure of CCIP4 showing layers of linked P atoms which ate arranged around screw axes perpendicular to the plane of the paper. 

Figure 6.1 Different presentations of the ideal perovskite ABO3 structure and the projections of structure along [1 0 0], [1 1 0], and [1 1 1].

PROJECTIONS OF STRUCTURES OF -ALUMINAS ON TO llo SIZES OF ATOMS APPROXIMATELY TO SCALE. 

The "SIMON" Project ("On-line acoustic monitoring of structural integrity of critical power plant components operating at high temperatures") had a duration of 4 years (1.10.1993 -30.09.1997) the Project Consortium included CISE (Project Coordinator, I), MITSUI BABCOCK ENERGY (UK), HERIOT-WATT UNIVERSITY (IK), PROET / EDP (P) and ENEL (I). 

As was said in the introduction (Section 2.1), chemical structures are the universal and the most natural language of chemists, but not for computers. Computers woi k with bits packed into words or bytes, and they perceive neither atoms noi bonds. On the other hand, human beings do not cope with bits very well. Instead of thinking in terms of 0 and 1, chemists try to build models of the world of molecules. The models ai e conceptually quite simple 2D plots of molecular sti uctures or projections of 3D structures onto a plane. The problem is how to transfer these models to computers and how to make computers understand them. This communication must somehow be handled by widely understood input and output processes. The chemists way of thinking about structures must be translated into computers internal, machine representation through one or more intermediate steps or representations (sec figure 2-23, The input/output processes defined... 

Another problem is to determine the optimal number of descriptors for the objects (patterns), such as for the structure of the molecule. A widespread observation is that one has to keep the number of descriptors as low as 20 % of the number of the objects in the dataset. However, this is correct only in case of ordinary Multilinear Regression Analysis. Some more advanced methods, such as Projection of Latent Structures (or. Partial Least Squares, PLS), use so-called latent variables to achieve both modeling and predictions. 

SONNIA can be employed for the classification and clustering of objects, the projection of data from high-dimensional spaces into two-dimensional planes, the perception of similarities, the modeling and prediction of complex relationships, and the subsequent visualization of the underlying data such as chemical structures or reactions which greatly facilitates the investigation of chemical data. 

It IS no accident that sections of our chair cyclohexane drawings resemble saw horse projections of staggered conformations of alkanes The same spatial relationships seen m alkanes carry over to substituents on a six membered ring In the structure... 

Aldoses exist almost exclusively as their cyclic hemiacetals very little of the open chain form is present at equilibrium To understand their structures and chemical reac tions we need to be able to translate Fischer projections of carbohydrates into their cyclic hemiacetal forms Consider first cyclic hemiacetal formation m d erythrose To visualize furanose nng formation more clearly redraw the Fischer projection m a form more suited to cyclization being careful to maintain the stereochemistry at each chirality center... 

Fig. 16.4. Silicate structures, (a) The Si04 monomer, (b) The Si207 dimer with a bridging oxygen. ( ) A chain silicate. (d) A sheet silicate. Each triangle is the projection of on Si04 monomer.

The absolute eonfiguration, (25, 45, 55 as shown or 2R,4R,5R), eannot be dedueed by NMR. For larger structures the insertion of the shift values and the coupling constants in the stereo projection of the struetural formula, from whieh one ean eonstruet a Dreiding model, proves useful in providing an overview of the stereoehemieal relationships. 

Fischer projection formulas can be used to represent molecules with several stereogenic centers and are commonly used for caibohydrates. For other types of structures, a more common practice is to draw the molecule in an extended conformation witii the main chain horizontal. In this arrangement, each tetrahedral caibon has two additional substituents, one facing out and one in. The orientation is specified widi solid wedged bonds for substituents facing out and with dashed bonds for substituents that point in. 

Fig. 10. Analysis of the atomic lattice images of the lead compound entering CNTs by capillary forces (a)detailed view of the high resolution image of the filling material, (b)tetragonal PbO atomic arrangement, note the layered structure and (c)tetragonal PbO observed in the [111] direction, note that the distribution of lead atoms follows the contrast pattern observable in (a), (d)bidimensional projection of the deduced PbO filling orientation inside CNTs as viewed in the tube axis direction, note that PbO layers are parallel to the cylindrical CNT cavity.

Refer to the Fischer projection of D-(+)-xylose in Figure 25.2 (Section 25.4) and give structural formulas for... 

Plane projection of the slructure or/ B gH2]. The two decaborane units are fused at the S(7 > and 6(6 ) positions to give a non rTJmetric structure with Cj symmetry... 

Figure 16.1 Structures of various allotropes of selenium and the structure of crystalline tellurium (a) the Seg unit in a- fi- and y-red selenium (b) the helical Se chain along the c-axis in hexagonal grey selenium (c) the similar helical chain in crystalline tellurium shown in perspective and (d) projection of the tellurium structure on a plane perpendicular to the c-axis.

Fig. 5. The projection of crystal structure of 97 (IQ) along the c-axis (hydrogen bonds are shown with heavy broken lines).

Figure 2. (001) projection of (a) AbTi3 and (b) AlnTi structures. A model for island-like precipitates composed of the core AlsTi3 phase and the periphery AlnTi phase is shown in (c), and (d) shows a schematic illustration of commensurate AbTia (small solid circles) and AlijTi (small open circles) diffraction patterns [14],... 

Fischer projections of, 980 Dacron, structure of, 819 Danishefsky, Samuel, 1002 Darzens reaction. 913 DCC (dicyclohexylcarbodiimide),... 

R)-Glyceraldehyde. Fischer projection of, 976 molecular model of, 976, 977 Glyceric acid, structure of. 753 Glycerol, catabolism of, 1132-1133 s/i-Glycerol 3-phosphate, naming of, 1132... 

Fig. 30. Projection of NH4NbOF4 structure on the planes (001) and (010). Reproduced from [204], V. 1. Pakhomov, T.A. Kaidalova, Kristallografiya 19 (1974) 733, Copyright 1974, with permission of Nauka (Russian Academy of Sciences) publishing.

Fig. 38. Projection of Na Fa OsF2 (II) structure (after Chaminade and Pouhard [192]).

The increased speed of structure determination necessary for the structural genomics projects makes an independent validation of the structures (by comparison to expected properties) particularly important. Structure validation helps to correct obvious errors (e.g. in the covalent structure) and leads to a more standardised representation of structural data, e.g. by agreeing on a common atom name nomenclature. The knowledge of the structure quality is a prerequisite for further use of the structure, e.g. in molecular modelling or drug design. 

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