This review is concerned with the structure and properties of liquid crystals. We do not discuss lyotropic systems, but only thermotropic liquid crystalline mesophases. Classification, identification method, and structural characteristics of thermotropic liquid crystals are described. Fundamental physical properties such as order parameter, dielectric anisotropy, birefringence and so on are also explained. The relation between molecular structure and liquid crystalline properties is discussed in detail. We showed that the examination of the mesomorphic behavior for the compounds incorporating an angular linkage is important for the study of the relation. The relation between molecular structure and the different physical properties is also reviewed.
Liquid crystalline compounds are one of a few examples of organic chemicals that are used in electronics in active mode. Since the discovery of an electro-optical effect of liquid crystals was first announced in 1968, numerous efforts have been made to result in a wide-spread applications of liquid crystal displays for calculators and watches which are commonly used nowadays because of their low power consumption and thinness. As the technology of micro-electronics is advanced, new applications of liquid crystal display for OA instruments, car instrument panels, flat TV's etc. have been developed and new display modes have been reported one after another. In this article, recent advances in liquid crystal applications (nematic, color display, cholesteric, smectic and polymeric) are described.
Certain types of metal oxides such as MgO, CaO, SrO, BaO, La2O3, CeO2, Y2O3, ThO2, ZrO2, and ZnO act as solid base catalysts for several types of reactions. This review describes the generation of the basic sites on thier surfaces, the catalytic characteristics in the reactions, and the structure of active sites. For generation of the basic sites, pretreatment of the metal oxides at elevated temperatures is required to remove strongly adsorbed H2O, CO2, and O2 from the surfaces. The catalytic behaviors of the solid base catalysts for the following reactions are explained ; double bond migration of olefins, alkynes, allenes, allylamines, and allyl ethers, hydrogenation of olefins, addition of amines to conjugated dienes, dehydrogenation and dehydration of alcohols, dehydrogenation and deamination of amines, dehydrogen halide of halogen compouds, alkylation of phenol, N-methylation of aniline, esterification of benzaldehyde, decomposition of diacetone alcohol, H2-D2 equilibration, and D exchange of olefins. A plausible structure of catalytically active sites is presented as surface cation-anion pairs in low coordinations.
Application of ultrafine metal particles, 10-1000 Å in diameter, to organic syntheses are reviewed as reagents and catalysts. Ultrafine magnesium particles are effectively reactive to organic compounds with rather poor reactivities such as fluorobenzenes and bromobenzenes, yielding the Grignard reagents. Ultrafine zinc particles also react with less reactive bromobenzenes under mild conditions. Ultrafine particles of palladium, platinum, rhodium, ruthenium, copper, and others show high catalytic activity and selectivity in various organic syntheses. The selective catalytic reactions involve 1) hydrogenation of C-C double bonds, nitro groups, and aromatic rings, 2) hydrogenation of dienes to the corresponding monoenes, 3) hydrogenolysis of cystine to cysteine, 4) hydration of acrylonitrile to acrylamide, and 5) hydration of C-C double bond, followed by dehydrogenation of the resulting alcohol. The features of ultrafine metal particles used in organic syntheses are discussed.
Utilizations of polymers for photoenergy conversion were reviewed with 156 references.Polymers can provide effective reaction fields in solution as well as in solid state for photoinduced charge separation and catalysis. Water photolysis with polymeric colloids was described. Possibilities of constructing photocells with polymer materials were discussed. A new type of photodiode based on photoinduced electron transfer was proposed.
This article describes a variety of C-C bond fission reactions of a cyclobutane ring formed by photoaddition of heteroaromatics containing an α, β-unsaturated carbonyl system in their ring systems to alkenes and other π2 components. The reactions are assisted by the strain involved in the four-membered ring and provide unique methods either for introduction of a variety of carbon chains or for annelation to heteroaromatic compounds.
Arachidonic acid is converted into biologically important substances, one of the most conspicuous being thromboxane A2 because of its outsanding potent platelet aggregating and smooth muscle contracting activities. Since thromboxane A2 is extremely labile, the synthesis of natural thromboxane A2 has not been reported yet. This review focuses the synthesis of thromboxane A2 analogs having the agonistic and antagonistic activities.