Mesomorphic property

The solubility of chitin is remarkably poorer than that of cellulose, because of the high crystallinity of chitin, supported by hydrogen bonds mainly through the acetamido group. Dimethylacetamide containing 5-9% liCl (DMAc/IiCl), and N-methyl-2-pyrrohdinone/LiCl are systems where chitin can be dissolved up to 5%. The main chain of chitin is rigid at room temperature, so that mesomorphic properties may be expected at a sufficiently high concentration [67,68]. 

Lateral monofluorination of the p-alkoxyphenyl isocyanide system [XAu (CNC6H40C H2 +i)] (X = C1, Br, I), in ortho-(3-F) (6a) and meta-(2-F) (6b) positions relative to the alkoxy chain was also studied [18]. None of the free fluorinated ligands is a LC, but their gold complexes display mesomorphic properties. This is a typical case of a promesogenic ligand which yields a mesogen upon coordination to a metal. 

Coco, S., Fernandez-Mayordomo, C., Falagan, S. and Espinet, P. (2003) Effect of alkoxy chains on the mesomorphic properties of (p-alkoxy)tetrafluoroarylgold(I) isocyanide complexes. Inorganica Chimica Acta, 350, 366-370. 

Zhang, S.-W., Ishii, R. and Takahashi, S. (1997) Syntheses and Mesomorphic Properties of Gold(I)-Carbene Complexes. Organometallics, 16, 20-26. 

Rod-like mononuclear derivatives have been prepared by the reaction of a polymeric alkynyl gold(I) complex with isocyanides. The mesomorphic properties of three types ofgold(I) acetylide complexes, namely, [Au(CC-Ar)(CN-Ar)J, [Au(CC-R)(CN-Ar)J and [Au(CC-Ar)(CN-R)] (Ar = aryl with aliphatic chain, R = alkyl chain), have been systematically examined. 

Liquid crystals, as the name implies, are condensed phases in which molecules are neither isotropically oriented with respect to one another nor packed with as high a degree of order as crystals they can be made to flow like liquids but retain some of the intermolecular and intramolecular order of crystals (i.e., they are mesomorphic). Two basic types of liquid crystals are known lyotropic, which are usually formed by surfactants in the presence of a second component, frequently water, and thermotropic, which are formed by organic molecules. The thermotropic liquid-crystalline phases are emphasized here they exist within well-defined ranges of temperature, pressure, and composition. Outside these bounds, the phase may be isotropic (at higher temperatures), crystalline (at lower temperatures), or another type of liquid crystal. Liquid-crystalline phases may be thermodynamically stable (enantiotropic) or unstable (monotropic). Because of their thermodynamic instability, the period during which monotropic phases retain their mesomorphic properties cannot be predicted accurately. For this reason it is advantageous to perform photochemical reactions in enantiotropic liquid crystals. 

In general, the following molecular moieties are helpful for the formation of mesomorphic properties ... 

TABLE 5. Mesomorphic properties of simple stilbene liquid crystals... 

Matsuda and coworkers investigated (1) the effect of a crown unit on the mesomorphic properties and (2) the behavior after complexation with suitable salts. These issues are still relevant today in current investigations. 

There have been only a few reports on crown ethers laterally attached to rod-like molecules in the last few years. Nevertheless, very interesting compounds have been synthesized in the past. The general problem of this compound class is the flexible crown ether itself that can destroy the mesomorphic properties when attached laterally. Making the rigid rod longer can circumvent this problem. Another way to obtain stable mesophases is the complexation with suitable salts. 

The most comprehensive studies on shape-persistent Hekates have been performed on stilbenoid star-shaped molecules. Structures and mesomorphic properties are collected in Table 1. Core building blocks with only one repeating unit per arm and one flexible chain 26a,b, 28a-d, 30a did not show any liquid crystal properties [56-58]. In the series of two chain derivatives 28e, 30b,c the formation of meso-phases depend on the core [57-59]. The electron deficient triazine and the dicyanopyridine building block induced obviously columnar mesophases. The pyridine derivative 30b showed only a crystalline phase [58]. In the series of nine chain stars 26c-g [60-62] and 28f-n [57], the compounds formed columnar phases depending on the chain length of the peripheral chains. Propyloxy chains are too short but hexyloxy and dodecyloxy chains are sufficient for the formation of liquid crystal phases by nanosegregation [60-62]. This can be rationalised by a dense... 

This method provides easy access to 4-alkylbenzoyl chlorides, which are useful intermediates in the preparation of diaryl esters that have mesomorphic properties.20 Benzoyl chlorides substituted in the 4-position also serve as starting materials for the preparation of aromatic aldehydes21 and nitriles,622 whereas the acids, derivable quantitatively from the acid chlorides, are good precursors via the Schmidt reaction to 4-substituted anilines.23... 

Independently of molecular mass and polydispersion degree, all cyclolinear carbosiloxane polymers with cyclic tetrasiloxane fragments (Table 15, polymers No 1 -6) and the ones with decamethylcyclo-hexasiloxane fragments (Table 15, polymers N°7-9) do not display mesomorphous properties. RSA data (Figure 14) indicate that polymers N°2 - 9 are amorphous, because their diffraction patterns are similar by type to these of amorphous polyorganosiloxanes. They contain two amorphous halos symmetrical intensive one at 20 (A 1/2 =1.8°) and diffuse low one at 20. 

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