Planar structure orientation

Here, however, it is possible to obtain stabilization of the low-dense lattice build-up of bulky molecules via intermolecular adhesion and orientation forces. Molecules with planar structural elements are advantageous in this respect since they are apt to support the lattice aggregate, and at the same time they are able to partition off cavities effectively. It is very convenient to use aromatic units. 

A complete analysis of the IR spectra of thienothiophenes 1 and 2 in the gaseous, liquid, and crystalline states was carried out by Kimel feld et a/. The following isotopically substituted compounds were also studied 2-deuterothieno[2,3-h]thiophene (l-2d), 2-deuterothieno[3,2-I)]-thiophene (2-2d), 2,5-dideuterothieno[2,3-h]thiophene (l-2,5-d2), and 2,5-dideuterothieno[3,2-h]thiophene (2-2,5-dj). The IR spectra of oriented polycrystalline films of all compounds were measured in polarized light, and Raman spectra of liquid thienothiophenes 1, l-2d, and 1-2,5-dj, of crystals of thienothiophenes 2 and 2-2,5-d2 and melts of thienothiophenes 2 and 2-2d were analyzed. The planar structure of point-group Cj, for thienothiophene 1 in the liquid and gaseous states was assumed. Then the thirty vibrations of compounds 1 and l-2,5-d2 can be divided into four symmetry classes Aj (11), Bj (10), A2 (4), and B2 (5) the vibrations of molecule (l-2d) (C, symmetry) are divided into two classes A (21) and A" (9). 

Three distinct structural types are available for a tetracoordinated fragment a square planar structure of symmetry, a nonplanar square pyramid with C4t> symmetry, a nonplanar structure with Cjv symmetry (which would result from the removal of two cis ligands from an octahedral MLg), and the tetrahedral structure of symmetry Td- These are shown in Figure 13.5 in the standard orientation. The orbitals of the Z>4/, structure... 

The carbon chain is in a planar zigzag orientation and forms an orthorhombic lattice with interpenetration of adjacent chains.61 As a result of this structure, ETFE has an exceptionally low creep, high tensile strength, and high modulus compared to other thermoplastic fluoropolymers. Interchain forces hold this matrix until the alpha transition occurs at about 110°C (230°F), where the physical properties of ETFE begin to decline and more closely resemble perfluoropolymers properties at the same temperature. Other transitions occur at -120°C (-184°F) (gamma) and about -25°C (-13°F) (beta).62... 

Table 3 shows the Tg values and solubility of some selected polyimides among those prepared from monomers of Tables 1 and 2. The combination of non-pla-nar dianhydrides and non-planar, raefa-oriented aromatic diamines containing flexible linkages provides the structural elements needed for solubility and melt processability. Some aromatic polyimides marketed as thermoplastic materials are based on these statements [9,57-60]. 

The C-H and C-C cr-bonds are all trigonal sp hybrids, with 120° bond angles. The two unhybridized p-orbitals form a 7r-bond, which gives the molecule its rigid planar structure. The two carbon atoms are connected by a double bond, consisting of one o and one tt. The third canonical form of 5/ -hybridization occurs in C-C triple bonds, for example, acetylene (ethyne). Here, two of the p AO s on each carbon remain unhybridized and can form two n -bonds, in addition to two (r-bonds. Acetylene H-C=C-H is a linear molecule, as shown below, since the p-hybrids are oriented 180° apart. 

It has been proposed that simple non-carbohydrate analogues containing the carboxylate and the acetylamino groups attached to a cyclic backbone spacer would be suflSdent to generate lead compoimds for further elaboration as NA inhibitors. The spacer would need to orient correctly these groups as found in bound DANA. It has been also required thad such compounds adopt a planar structure near the carboxylate to mimic the transition state and be able to present additional side-chain functionality for interaction with other conserved amino acid residues in the sialic acid binding site. 

The probable explanation of this distortion is that it permits an approximation to the staggered orientation about four of the five carbon-carbon bonds (see Ethane, plate 17). The planar structure would involve the unstable orientation for all five bonds. 

---