Star-Like Compounds

Vorlander also had the idea to look for mesogenic properties in the cases of star-like or cross-like molecules, however, his coworker did not have any success in this area [5, 6]. About 1977, Chandrasekhar et al. [7] and Billard et al. [8] were, independently, able to prove that disk-like molecules can in fact form mesophases, called columnar phases. Since then, several hundred discotic compounds have been synthesized [9-14]. 

During his systematic investigations, Vorlander had already found liquid crystal- 

Vorlander also investigated the influence of the length of the molecules on their mesomorphic properties, and during these investigations he made the first observation of oligomeric or polymeric liquid crystals [17], Stimulated by the aim of producing superstrong fibres, polymer liquid crystals have been synthesized systematically since about 1967 [22], and at present many different varieties are known. 

The clear dependence of the mesomorphic properties on the geometrical shape of the molecule has allowed the derivation of simple models for describing the systems theoretically. 

Calamitic and discotic compounds can be described theoretically using the same basic model, i.e. the cylinder, by elongation or compression, respectively, of the central axis of the cylinder [23]. Of course, the cylinder model is a oversimplification of real mesogenic molecules. As most of the compounds contain ring systems, which are somewhat flat, it could be proposed that parallelepipeds provide better models. In fact, such models have been used for molecular-statistical theories, and these have allowed the description of, in addition to calamitic and discotic molecules, flat elongated (board-like, sanidic) molecules [24]. 

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A rise in the trifunctional unit content from 0 to 1.4 mol% in oligomethylethylsiloxanes leads to sharp growth of the kinematic viscosity. There is a great probability therewith of formation of star-like compounds, and lateral branch lengths exceed a definite critical point, thus resulting in a viscosity increase. A further rise in the trifunctional unit content up to 16.9 mol% results in a kinematic viscosity drop. 

Many micellar catalytic applications using low molecular weight amphiphiles have already been discussed in reviews and books and will not be the subject of this chapter [1]. We will rather focus on the use of different polymeric amphiphiles, that form micelles or micellar analogous structures and will summarize recent advances and new trends of using such systems for the catalytic synthesis of low molecular weight compounds and polymers, particularly in aqueous solution. The polymeric amphiphiles discussed herein are block copolymers, star-like polymers with a hyperbranched core, and polysoaps (Fig. 6.3). 

The first two compounds are greenish blue, the latter are light violet in colour. All are crystalline, and separate in star-like crystals. In concentrated solution the separation of the compounds is almost quantitative.5... 

Star-like tetraelement compounds (138 and 139) containing a central coordinatively unsaturated Ga or In atom attached to three dialkylelement groups in a planar environment were obtained by the oxidation of the corresponding anions with dry air (138)219 or by treatment of the tetraaryldiindium starting compound 58 with elemental lithium (139).124... 

An American psychedelic morning glory (Ipomoea violaceaj. This species includes plants popularly known as "Heavenly Blue, "Pearly Gates, "Wedding Bells, "Summer Skies and "Blue Star —all of which contain LSD-like compounds. 

Anderson, L. Bohlin, L. lorizzi, M. Riccio, R. Minale, L. Moreno-Lopez, W. Biologically Active Saponins and Saponin-Like Compounds from Starfish and Brittle-Stars. Toxicon. 1989, 27, 179-188. 

A similar condensation of a-dicarbonyl compounds with a 2,4,6-trisubstituted pyridine bearing three amidrazonyl fragments gave the star-like heterocyclic ensembles 214-218 (Figure 13) <1998TL8817>. 

Filippov, A. R Romanova, O. A. Vinogradova, L. V Molecular and hydrodynamical characteristics of star-like polystirenes with one or two molecules of fullerene C as branching center. High-Molecular Compounds. A, 2010,52(3), 371-377. 

Discotic architectures that use a central triphenylene core with six peripheral triphenylene units also exhibit colunmar mesophases, and these are commonly called star-like liquid crystals. Compoimd 28 is a very large molecule that uses flexible spacers to attach peripheral triphenylene units to a central discotic core in a star-like manner. The hexagonal columnar phase of compound 28 has been identified as hexagonal. Such stractmes are ohgomeric and could almost be considered polymeric (see Chapter 5). 

Many compounds with multiple active halogen atoms have been used to initiate bi- or multi-directional growth to form ABA block copolymers and star-like polymers and copolymers [158]. Active halogens can be incorporated at the chain ends of polymers... 

Cobalt-catalyzed cycloaddition reactions of symmetrical alkynes usually generate Cg-symmetric hexaphenylbenzenes (Pisula et al., 2004 Chebny et al., 2006). Synthesis of the star-shaped compound 14, which contains six ort/io-carborane clusters surrounding a hexaphenylbenzene core (Figure 26.3) was synthesized in a like manner. Heximer 14 was then decapitated in a methanolic sodium hydroxide solution to convert the neutral cZoio-carboranes into their corresponding [nido-C2B9H,o] cages, as shown for 15, imparting water solubility (Dash et al., 2009). 

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