Orientation, atomic

The dielectric constant is a measure of the ease with which charged species in a material can be displaced to form dipoles. There are four primary mechanisms of polarization in glasses (13) electronic, atomic, orientational, and interfacial polarization. Electronic polarization arises from the displacement of electron clouds and is important at optical (ultraviolet) frequencies. At optical frequencies, the dielectric constant of a glass is related to the refractive index k =. Atomic polarization occurs at infrared frequencies and involves the displacement of positive and negative ions. 

There is another possible consequence of a collision between two fluorine atoms. The two atoms can remain together to form a molecule. Each atom has a valence electron in a half-filled orbital. We can imagine these two atoms orienting so that these half-filled" orbitals overlap in space. Then the half-filled" valence orbital of... 

The intensity of the EPR resonance absorption is a measure of the number of paramagnetic centres present [346], while the type of line observed and the measured g factor are indications of the interactions of the paramagnetic particles and of their distribution within the matrix. Such spectra are much more sensitive to changes in crystal field and atomic orientations than X-ray diffraction and are not dependent upon crystallinity [347]. The nature of the paramagnetic particles may be discerned from the superfine structure of the spectrum. 

Axial hydrogens the hydrogen atoms orient in a direction that is generally perpendicular to the average of the ring of carbon atoms. 

In the chemical deformation densities introduced by Schwarz and collaborators, the density and the orientation of the atoms is quantitatively defined by variation of the atomic orientation and orbital population such as to minimize the space integral over the squared deformation density (Schwarz et al. 1989, Mensching et al. 1989). 

Hirshfeld (1984) found the electrostatic charge balance at the F nuclei, based on the experimental deformation density, to be several times more repulsive (i.e., anti-bonding) than that of the promolecule. Very sharp dipolar functions at the exocyclic C, N, and F atoms, oriented along the local bonds, were introduced in a new refinement in which the coefficients of the sharp functions were constrained to satisfy the electrostatic Hellmann-Feynman theorem (chapter 4). The electrostatic imbalance was corrected with negligible changes in the other parameters of the structure. The model deformation maps were virtually unaffected, except for the innermost contour around the nuclear sites. 

A p orbital on the central atom, oriented perpendicular to the molecular plane. 

Six Charge Clouds Six charge clouds around an atom orient toward the six corners of a regular octahedron, a geometric solid whose eight faces are equilateral triangles. All six positions are equivalent, and the angle between any two adjacent positions is 90°. 

If the interpretation of the results, shown in Figure 16, is correct and the hydrogenolysis product of methyl gibberellate has a trans ring A/B fusion with the C-10a hydrogen atom -oriented then some recent results of ours (18) provide proof that the lactone is, in fact, -oriented. The argument is as follows (Figure 18) ... 

Syn selectivity in the epoxidation of allylic fluorides by peracids has been interpreted by electronic stabilization of the transition state with the electronegative fluorine atom oriented at the inside position304. 

Although other Fischer projections may be drawn by rotating the perspective view in other directions, the one shown is preferred because it has the longest chain of carbon atoms oriented on the vertical axis with the lowest numbered carbon at the top. 

Other multidentate ligands have been prepared and their structures determined. The bisphosphinine 64 crystallized with the two phosphinine planes almost orthogonal (91.59°), and the two phosphorus atoms oriented away from each other (P-P distance 5.8 A). However, even at low temperature (—95 °C) there was no evidence in either the 31P... 

Several forms of the superoxide 02 radical ion formed on the surface of ZnO, MgO, CoO/MgO and Si02 have been reported in [40, 83]. The species were differed by the orientation of the 0-0 residue relatively the surface and the metal ion Mn+. The correlation between distances and angles in the most probable structures with the experimentally measured gz values was found, and the dynamic behaviour observed in some cases was also discussed [83], Calculated EPR spectra of the adsorbed 02 for different charges of the metal ion Mn+ (2 < n < 6) showed that gz values are sensitive to the ionic charge and the increase of n+ causes the decrease of gz [83]. The z-axis of the tensor is usually in the direction of the internuclear axis and the x- direction is that of the mole-cular orbital hosting the unpaired electron. The data in Table 8.3 show that the dependen-ce of gz on n+ is, however, valid quantitatively not always because of rather many factors affecting the gz value (distances to the neighbouring atoms, orientation, local fields, etc.). Additional detailed information can be found in references cited in this section. 

Stereoregularity. The addition of monomer fixes the tacticity of the previous monomer unit. Syndiotactic structure has the adjacent chlorine atoms oriented to opposite sides of the carbon—carbon—carbon plane, whereas isotactic structure has the adjacent chlorine atoms oriented to same side of the carbon—carbon—carbon plane. The potential energy for syndiotactic conformation is 4.2—8.4 kj/mol (1—2 kcal/mol) lower than for isotactic conformation (74,75). Thus the ratio of propagation rates for syndiotactic to isotactic, kjk, must increase with decreasing temperature. Consequently, with decreasing polymerization temperature, the degree of syndiotacticity in PVC should increase. Measured amounts of syndiotacticity are illustrated in Figure 8... 

Figure 14 Schematic view of the framework of 10. Note the four -OH hydrogen atoms oriented into the cavity pairwise at the upper left and lower right of the structure.

Example Number of Groups of Electrons Number of Attached Atoms Orientation of Electron Groups Shape of Molecule... 

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