Crystal compounds

A Hquid crystal compound in more cases than not takes on more than one type of mesomorphic stmcture as the conditions of temperature or solvent are changed. In thermotropic Hquid crystals, transitions between various phases occur at definite temperatures and are usually accompanied by a latent heat. 

The covalent compounds of graphite differ markedly from the crystal compounds. They are white or lightly colored electrical insulators, have Hi-defined formulas and occur in but one form, unlike the series typical of the crystal compounds. In the covalent compounds, the carbon network is deformed and the carbon atoms rearrange tetrahedraHy as in diamond. Often they are formed with explosive violence. 

A. R. Ubbelohde and F. A. Lewis, Graphite and Its Crystal Compounds, Oxford University Press, London, 1960. 

Telluradiazolines are thermally stable crystal compounds, but they are very sensitive to light. When exposed to daylight, telluradiazolines undergo rapid decomposition, even in the solid state. By heating degassed solutions of telluradiazoline 79a in deuterochloroform or benzene, telluroketone 85 and alkenes 81 and 82 are formed in almost quantitative yield (93JA7019). 

The free selenazole hydrazines are solids, sometimes well crystallized compounds. They show the typical properties of hydrazines. Thus they reduce Fehling s solution on warming and liberate silver, even in the cold, from ammoniacal silver nitrate solution. Further, they react with carbonyl compounds for example, benzylidene hydrazones are formed with benzaldehyde. These are identical with the hydrazones formed by direct condensation from benzaldehyde selenosemicarbazone and the corresponding a-halogenocarbonyl compound. 2-Hydrazino-4-phenylselenazole has also been reacted with acetophenone. The 2-a-methylbenzylidenehydrazone of 4-phenyl-selenazole (2, K = CJl, R" = H, R" = NH—N CMe-aH ) forms golden yellow plates mp 171°C. ... 

Ubbelode AR, Lewis FA (1960) Graphite and its crystal compounds, Oxford Univ. Press... 

The formation of surface defects of a crystal lattice. It was observed while using crystal compounds of transition metals as catalysts [e.g. as was shown by Arlman (171, 173), for a TiCl3 surface defects appear on the lateral faces of the crystal]. In this case low surface concentration of the propagation centers should be expected, as is illustrated in the case of polymerization by titanium dichloride (158). The observed... 

Ul. Ubbelohde, A. R., and Lewis, F. A., "Graphite and its Crystal Compounds Oxford Univ. Press (Clarendon) London and New York, 1960. 

Visual inspechon frequently cannot differenhate between an amorphous or crystalline material, e.g. at Pfizer medicinal chemists were required to submit only crystalline and not amorphous compounds to an automated thermodynamic solubility assay. In prachce half the white powders that they produced for the assay and that they thought were crystalline were actually amorphous. Prior to 2000 the vast majority of these medicinal chemistry labs had no melting point equipment and it was only in 2000 that the pharmaceuhcal sciences department started a workshop to teach medicinal chemists the importance of solid state properhes, how to crystallize compounds and the importance of salt forms. 

Fig. 7 Microphotograph of the crystal compounds under three channels LSCM beams (see Procedure). Excitation by wavelengths 488, 543 nm and 633 nm. Chlorophyll or carotenoids are a sum of chlorophylls a and b or a sum of carotenoids from pea leaves purified on silicagel.

By using slightly different words, approximants are translationally normal crystal compounds generally with large unit cells that contain condensed, highly symmetric building blocks such as dodecahedra and icosahedra and have compositions close to those of related quasicrystals. 

Compound solution b crystal Compound solution b crystal... 

Rubidium cobalt sulfate (Rb SO CoSO 6HjO) is an example of several double sulfates that rubidium has the ability to form. Rubidium cobalt sulfate is a combined rubidium-cobalt compound in the form of ruby-red crystals. Other rubidium sulfate crystal compounds and their colors are rubidium + copper = white rubidium + iron = dark green and rubidium + magnesium = colorless. 

The solid product is seldom pure when obtained from a chemical reaction, being contaminated with various impurities, reagents and byproducts. For purification, the process of crystallization, sometimes called recrystallization, is generally employed When dealing with large quantity formulas, the utmost care should be taken to obtain the maximum yield of a pure crystallized compound. 

X-ray crystallography is the most accurate method for structural elucidation of flavonoids in the solid state. The method can only be applied to crystallized compounds, which has limited the number of flavonoid crystal structures reported. 

Title Polymerizable Liquid-Crystal Compound, Liquid-Crystal Composition, Optical Anisotropic Material, and Optical Element... 

Polymerizable Liquid-Crystal Compound, Liquid-Crystal Composition... 

Nematic phase this is the simplest structure. It is the most disordered mesophase and therefore very fluid. It is called N. In the nematic phase, the molecules are ordered mainly in one dimension with their long axes parallel, and they are free to move parallel to this axis (there is no long-range order). Nematic liquid crystal mixtures, containing various amounts of different liquid crystal compounds, are used in electro-optic display systems such as flat-panel displays. 

The redox chemistries of di-, tri and tetra-nuclear Mo—S cyanide complexes have been discussed in relation to their electronic structures.135 Passage of oxygen into an aqueous solution of [Mo2S2(CN)s]6 leads to the formation of a dark violet mixed-crystal compound of the composition K4+J,[Mo2(S02)(S2)(CN)8] [Mo2(S02)(S2)(CN)8]1 -4H20 (x = 0.3). In the crystal the two anions, whilst structurally similar, are located at crystallographically independent positions each involves both molybdenum atoms surrounded by an approximately... 

Organic Adsorbents. (a) Organic crystal compounds (e.g., benzophenone on firebrick, anthraquinone on graphitized carbon black, phthalic anhydride and/or phthalic acid isomers on Chromo-sorb G). (b) Liquid phases below their melting point (e.g.,... 

Due to the large number of known liquid crystal compounds, some common structure... 

The ability of the boron atom of 59 to engage in a donor-acceptor interaction was illustrated with DMAP and DABCO (DABCO = diazabi-cyclo-[2.2.2]-octane) that readily formed the corresponding Lewis adducts. Interestingly, a similar behavior was retained after coordination of the phosphorus atom to palladium. The formation of the Lewis base adducts 66a and 66b of complex 65 (Scheme 38) was supported by solid-state 31P and nB CP/MAS-NMR spectroscopy (<5 1 B = 5-6 ppm), although the occurrence of decomposition and/or dissociation processes impeded spectroscopic characterization in solution and recrystallization to obtain X-ray quality crystals. Compounds 66a and 66b substantiate the ability of ambiphilic compounds to engage concomitantly into the coordination of donor and acceptor moieties. Such a dual behavior opens interesting perspectives for the preparation of metallo-polymers and multimetallic complexes. 

Methods for the synthesis of calcium hydroxyapatite have been reported in the past,1,2 but all of them produced either poorly crystallized or somewhat impure products. The following procedure produces a very well-crystallized compound which has a high degree of purity. The reaction is simply the hydrolysis of calcium monohydrogen phosphate to hydroxyapatite in a closed system. The major disadvantage is the small amount of material obtained from each hydrolysis because of the small capacity of the bombs used. Larger reaction vessels would minimize this objection. 

Another example of a different type of correlation of structural to photophysical properties is shown in a study of a unique terbium compound [63]. This compound will be briefly discussed and is depicted in Figure 7.9 with its nonlinear emission properties with excitation at 800 nm. The photophysical properties are atypical and rather extraordinary due to the unusual molecular structure of the co-crystallization compound (4) of the organic chromophore and the terbium salt This compound shows both multiphoton absorption induced green f-f emission from the terbium ion as well as second-harmonic generation. However, unlike previously... 

We have found that nearly all of the compounds that stabilize MTs also stabilize the 2-D crystals. Compounds that have been used include paclitaxel, epothilone-A and B, discodermolide and eleutherobin. Laulimalide, however, disrupts the sheets and causes them to reform into MTs. Microtubule destabilizing compounds have also been found to disrupt the crystals. 

Uses Alachlor is a colorless to yellow crystal compound.111 13 Alachlor is an aniline herbicide used to control annual grasses and broadleaf weeds in field corn, soybeans, and peanuts. It is a selective systemic herbicide, absorbed by germinating shoots and roots. It works by interfering with a plant s ability to produce protein and by interfering with root elongation. This compound is one of the most extensively used herbicides. The USEPA categorizes alachlor under restricted use pesticides (RUP), and it should be purchased and used only by certified applicators. 

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