Spatial orientation

Space isomerism or stereo-isomerism, due to differences only in the spatial orientation of the atoms in the molecule. 

Figure C3.4.1. Example of the spatial orientation of tlrree major vectors / Aaird R, unit vectors of tire donor...

T is a rotational angle, which determines the spatial orientation of the adiabatic electronic functions v / and )/ . In triatomic molecules, this orientation follows directly from symmetry considerations. So, for example, in a II state one of the elecbonic wave functions has its maximum in the molecular plane and the other one is perpendicular to it. If a treatment of the R-T effect is carried out employing the space-fixed coordinate system, the angle t appearing in Eqs. (53)... 

The representation of molecular properties on molecular surfaces is only possible with values based on scalar fields. If vector fields, such as the electric fields of molecules, or potential directions of hydrogen bridge bonding, need to be visualized, other methods of representation must be applied. Generally, directed properties are displayed by spatially oriented cones or by field lines. 

Each set of p orbitals has three distinct directions or three different angular momentum m-quantum numbers as discussed in Appendix G. Each set of d orbitals has five distinct directions or m-quantum numbers, etc s orbitals are unidirectional in that they are spherically symmetric, and have only m = 0. Note that the degeneracy of an orbital (21+1), which is the number of distinct spatial orientations or the number of m-values. 

The funetions with m quantum numbers ean be eombined in pairs to give the spatially oriented funetions with whieh most ehemists are familiar ... 

When writing the constitution of a molecule it is not necessary to concern your self with the spatial orientation of the atoms There are many other correct ways to represent the constitution shown What is important is to show the connectiv ity OCCN (or its equivalent NCCO) and to have the correct number of hydrogens on each atom... 

Table 4.14 Spatial Orientation of Common Hybrid Bonds Figure 4.1 Crystal Lattice Types Table 4.15 Crystal Structure...

TABLE 4.14 Spatial Orientation of Common Hybrid Bonds... 

Retention of configuration (Section 6.13) Stereochemical pathway observed when a new bond is made that has the same spatial orientation as the bond that was broken. 

The aromatic portion of the molecules discussed in this chapter is frequently, if not always, an essential contributor to the intensity of their pharmacological action. It is, however, usually the aliphatic portion that determines the nature of that action. Thus it is a common observation in the practice Ilf medicinal chemistry that optimization of potency in these drug classes requires careful attention to the correct spatial orientation of the functional groups, their overall electronic densities, and the contribution that they make to the molecule s solubility in biological fluids. These factors are most conveniently adjusted by altering the substituents on the aromatic ring. 

Two pictures of two spatial (three-dimensional) models can represent the same structural formula without representing the same stereoformula they describe the same structural formula if they exhibit the same relationships (if they are topologically congruent, i.e., they satisfy conditions (I), (II), (III)). In order to describe the same stereoformula they must display the same relationships and the same spatial orientation [they satisfy (I), (II), (III), and in addition (IV) (with A ), that is, be spatially congruent]. If two formulas viewed as stereoformulas are equal then they are certainly equal when they are treated as structural formulas. Consequently there are at least as many stereoisomers as there are structural isomers. This fact is reflected by (2.8). It is true particularly for paraffins and monosubstituted paraffins. 

Conformational isomers are represented in two ways, as shown in Figure 3.6. A sawhorse representation views the carbon-carbon bond from an oblique angle and indicates spatial orientation by showing all C-Tl bonds. A Newman projection views the carbon-carbon bond directly end-on and represents the two carbon atoms by a circle. Bonds attached to the front carbon are represented by lines to the center of the circle, and bonds attached to the rear carbon are represented by lines to the edge of the circle. 

Unlike the constitutional isomers butane and isobutane (Section 3.2), which have their atoms connected in a different order, the two 1,2-dimethyl-cyclopropanes have the same order of connections but differ in the spatial orientation of the atoms. Such compounds, which have their atoms connected in the same order but differ in three-dimensional orientation, are called stereochemical isomers, or stereoisomers. 

The physical and chemical properties of complex ions and of the coordination compounds they form depend on the spatial orientation of ligands around the central metal atom. Here we consider the geometries associated with the coordination numbers 2,4, and 6. With that background, we then examine the phenomenon of geometric isomerism, in which two or more complex ions have the same chemical formula but different properties because of their different geometries. 

Two or more species with different physical and chemical properties but the same formula are said to be isomers of one another. Complex ions can show many different kinds of isomerism, only one of which we will consider. Geometric isomers are ones that differ only in the spatial orientation of ligands around the central metal atom. Geometric isomerism is found in square planar and octahedral complexes. It cannot occur in tetrahedral complexes where all four positions are equivalent... 

The hippocampus, which got its name from the Greek word for seahorse, due to its form, is a nucleus in the depth of the temporal lobe. The hippocampus is important for the integration of sensory information, for spatial orientation and for memory formation. The hippocampal formation contains the CA (cornu ammonis) regions, the dentate gyms and the subiculum. 

This separation is an impressive example of an entropically driven distribution system where the normally random movements of the solute molecules are restricted to different extents depending on the spatial orientation of the substituent groups. For further information the reader is directed to an excellent review of chiral separations by LC (Taylor and Maher (12)) and a monograph on CYCLOBOND materials from ASTEC Inc. (13). 

The dependence of the j3-deuterium effect on the spatial orientation of the isotopic bond with respect to the developing -orbital, on the a-carbon atom was elegantly demonstrated by Shiner and Humphrey (1963). This work will not be discussed in detail here suffice it to say the suggestion is made that j8-deuterium effects are better correlated by the postulate of hyperconjugation and its angular dependence than by the simple steric model (Shiner and Humphrey, 1963). 

A planar complex of the type [Pt(NH3)2Cl2] can exist in two forms depending upon the relative spatial orientation of the two chloride ligands. They can be at 90° to each other to give the cis form (1.1), or at 180° to give the trans isomer (1.2). 

Monosaccharides can differ in their formulas, their ring sizes, and the spatial orientations of their hydroxyl groups. To analyze the differences between two monosaccharides, begin with structural drawings of the molecules, oriented so the ether linkages are in comparable positions. Then examine the stmctures to locate differences in constituents and bond orientations. 

The elimination of HX(X = SOCH3, SCHj) from the [M-STol]- and [MH-HSTol] cations (Tol = CHjCgH ) from 5-9 under electron impact and chemical ionization depends strongly on the spatial orientation of the vicinal substituents . The intensity of the [M — STol] ion is appreciably higher when X and Y are cis than when they are trans. The stereochemistry of the sulfoxide group is not important since 7 and 8 exhibit very similar spectra. The elimination of HSOCHj occurs more easily from 7 and 8... 

Protein arrays may offer advantages over libraries. The array format provides a precise spatially oriented grid that allows side-by-side comparison of assay results for all of the proteins on the array. The spatial arrangement also permits immediate identification of a clone that tests positive in an assay based on its location on the array. Therefore, less effort is required to identify the protein responsible for an interaction than with a library screen. A disadvantage of a protein array, however, is that fewer proteins can be efficiently arrayed and screened ( 104) versus a library ( 109). Therefore, the number of elements that can be effectively arrayed and assayed currently limits protein arrays. 

Figure 7 (A) Spatial orientation of intercellular junctions within an epithelial cell mono-...

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