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Polysilicon Halides
Polysilicon halides are silicon-backbone polymeric solids. At room temperature, the polysilicon fluorides are colorless to yellow solids while the chlorides, bromides, and iodides are, respectively, yellow, amber, and red-orange. Polysilicon dihalides (perhalo- polysilenes) have the general formula (Si''X''2)n while the polysilicon monohalides (perhalo- polysilynes) have the formula (Si''X'')''n'', where ''X'' is F, Cl, Br, or I and ''n'' is the number of monomer units in the polymer. Macromolecular structure The polysilicon halides can be considered structural derivatives of the polysilicon hydrides, in which the side-group hydrogen atoms are substituted with halogen atoms. In the monomeric silicon dihalide (aka dihalo-silylene and dihalosilene) molecule, which is analogous to carbene molecules, the silicon atom is divalent (forms two bonds). By contrast, in both the polysilicon dihalides and the polysilicon monohalides, as well as the polysilicon hydrides, the silicon atom i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Backbone Chain
In polymer science, the polymer chain or simply backbone of a polymer is the main chain of a polymer. Polymers are often classified according to the elements in the main chains. The character of the backbone, i.e. its flexibility, determines the properties of the polymer (such as the glass transition temperature). For example, in polysiloxanes (silicone), the backbone chain is very flexible, which results in a very low glass transition temperature of . The polymers with rigid backbones are prone to crystallization (e.g. polythiophenes) in thin films and in solution. Crystallization in its turn affects the optical properties of the polymers, its optical band gap and electronic levels. Organic polymers : Common synthetic polymers have main chains composed of carbon, i.e. C-C-C-C.... Examples include polyolefins such as polyethylene ((CH2CH2)n) and many substituted derivative ((CH2CH(R))n) such as polystyrene (R = C6H5), polypropylene (R = CH3), and acrylates (R = CO2R'). O ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lability
Lability refers to something that is constantly undergoing change or is likely to undergo change. Biochemistry In reference to biochemistry, this is an important concept as far as kinetics is concerned in metalloproteins. This can allow for the rapid synthesis and degradation of substrates in biological systems. Biology Cells Labile cells refer to cells that constantly divide by entering and remaining in the cell cycle. These are contrasted with "stable cells" and "permanent cells". An important example of this is in the epithelium of the cornea, where cells divide at the basal level and move upwards, and the topmost cells die and fall off. Proteins In medicine, the term "labile" means susceptible to alteration or destruction. For example, a heat-labile protein is one that can be changed or destroyed at high temperatures. The opposite of labile in this context is "stable". Soils Compounds or materials that are easily transformed (often by biological activity) are termed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polytetrafluoroethylene
Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. It is one of the best-known and widely applied PFAS. The commonly known brand name of PTFE-based composition is Teflon by Chemours, a spin-off from DuPont, which originally discovered the compound in 1938. Polytetrafluoroethylene is a fluorocarbon solid, as it is a high-molecular-weight polymer consisting wholly of carbon and fluorine. PTFE is hydrophobic: neither water nor water-containing substances wet PTFE, as fluorocarbons exhibit only small London dispersion forces due to the low electric polarizability of fluorine. PTFE has one of the lowest coefficients of friction of any solid. Polytetrafluoroethylene is used as a non-stick coating for pans and other cookware. It is non-reactive, partly because of the strength of carbon–fluorine bonds, so it is often used in containers and pipework for reactive and corrosive chemicals. Where used as a lubricant, PTFE ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trichlorosilane
Trichlorosilane is an inorganic compound with the formula HCl3Si. It is a colourless, volatile liquid. Purified trichlorosilane is the principal precursor to ultrapure silicon in the semiconductor industry. In water, it rapidly decomposes to produce a siloxane polymer while giving off hydrochloric acid. Because of its reactivity and wide availability, it is frequently used in the synthesis of silicon-containing organic compounds. Production Trichlorosilane is produced by treating powdered metallurgical grade silicon with blowing hydrogen chloride at 300 °C. Hydrogen is also produced, as described in the chemical equation: :Si + 3 HCl → HCl3Si + H2 Yields of 80-90% can be achieved. The main byproducts are silicon tetrachloride (chemical formula SiCl4), hexachlorodisilane (Si2Cl6) and dichlorosilane (H2SiCl2), from which trichlorosilane can be separated by distillation. It is also produced from silicon tetrachloride: :Si + 3 SiCl4 + 2 H2 → 4 HCl3Si Application ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Infrared Multiphoton Dissociation
Infrared multiple photon dissociation (IRMPD) is a technique used in mass spectrometry to fragment molecules in the gas phase usually for structural analysis of the original (parent) molecule. How it works An infrared laser is directed through a window into the vacuum of the mass spectrometer where the ions are. The mechanism of fragmentation involves the absorption by a given ion of multiple infrared photons. The parent ion becomes excited into more energetic vibrational states until a bond(s) is broken resulting in gas phase fragments of the parent ion. In the case of powerful laser pulses, the dissociation proceeds via inner-valence ionization of electrons. IRMPD is most often used in Fourier transform ion cyclotron resonance mass spectrometry. Infrared photodissociation spectroscopy By applying intense tunable IR lasers, like IR- OPOs or IR free electron lasers, the wavelength dependence of the IRMPD yield can be studied. This infrared photodissociation spectroscopy all ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disproportionation
In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can be applied to any desymmetrizing reaction of the following type, regardless of whether it is a redox or some other type of process: :2A -> A' + A'' Examples *Mercury(I) chloride disproportionates upon UV-irradiation: :Hg2Cl2 → Hg + HgCl2 *Phosphorous acid disproportionates upon heating to give phosphoric acid and phosphine: :4 → 3 H3PO4 + PH3 *Desymmetrizing reactions are sometimes referred to as disproportionation, as illustrated by the thermal degradation of bicarbonate: :2 → + H2CO3 :The oxidation numbers remain constant in this acid-base reaction. This process is also called autoionization. *Another variant on disproportionation is radical disproportionation, in which two radicals form an alkene and an alkane. : Reverse r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oligomer
In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relative molecular mass, the structure of which essentially comprises a small plurality of units derived, actually or conceptually, from molecules of lower relative molecular mass.'' The name is composed of Greek elements '' oligo-'', "a few" and '' -mer'', "parts". An adjective form is ''oligomeric''. The oligomer concept is contrasted to that of a polymer, which is usually understood to have a large number of units, possibly thousands or millions. However, there is no sharp distinction between these two concepts. One proposed criterion is whether the molecule's properties vary significantly with the removal of one or a few of the units. An oligomer with a specific number of units is referred to by the Greek prefix denoting that number, wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comproportionation
Comproportionation or synproportionation is a chemical reaction where two reactants containing the same element but with different oxidation numbers, form a compound having an intermediate oxidation number. It is the opposite of disproportionation.Shriver, D. F.; Atkins, P. W.; Overton, T. L.; Rourke, J. P.; Weller, M. T.; Armstrong, F. A. “Inorganic Chemistry” W. H. Freeman, New York, 2006. . Frost diagrams The tendency of two species to disproportionate or comproportionate can be determined by examining the Frost diagram of the oxidation states; if a species' value of Δ''G''/''F'' is lower than the line joining the two oxidation numbers on either side of it, then it is more stable and if in a solution, these two species will undergo comproportionation. A Frost Diagram is another way of displaying the reduction potentials for the various oxidation states of a given element, X. It shows nE against the oxidation number N: here, E is the reduction potential for the X(N)/X(0) c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disilene
Disilene is an inorganic compound with the chemical formula . The name ''disilene'', referring to the structure of a particular prototropic tautomer of the molecule. It is the simplest silene. Properties and bonding Disilene is a molecule with one Si=Si bond, and four equivalent Si-H bonds. Unlike ethylene, disilene is kinetically unstable with respect to tautomerisation. Disilene has two other tautomers, that are very close in energy: (μ2-''H'')disilene, and disilanylidene. Organodisilenes Disilenes bearing sterically bulky substituents are isolable and have been well characterized although they remain mainly of academic interest. The first stabilised disilene was tetramesityldisilene, (C6Me3H2)4Si2. The Si=Si distance in this molecule is 2.15 Å, about 10% shorter than a typical Si–Si single bond. The Si2C4 core is roughly planar. Such species are typically prepared by reduction of organosilicon halides: :2 R2SiCl2 + 4 Na → R2Si=SiR2 + 4 NaCl. An alternative synthesi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. Their consequently large molecular mass, relative to small molecule compounds, produces unique physical properties including toughness, high elasticity, viscoelasticity, and a tendency to form amorphous and semicrystalline structures rather than crystals. The term "polymer" derives from the Greek word πολύς (''polus'', meaning "many, much") and μέρος (''meros'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
