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Silylidene
Silylene is a chemical compound with the formula SiH2. It is the silicon analog of methylene, the simplest carbene. Silylene is a stable molecule as a gas but rapidly reacts in a bimolecular manner when condensed. Unlike carbenes, which can exist in the singlet or triplet state, silylene (and all of its derivatives) are singlets. Silylenes are formal derivatives of silylene with its hydrogens replaced by other substituents. Most examples feature amido (NR2) or alkyl/aryl groups. Silylenes have been proposed as reactive intermediates. They are carbene analogs. Synthesis and properties Silylenes are generally synthesized by thermolysis or photolysis of polysilanes, by silicon atom reactions (insertion, addition or abstraction), by pyrolysis of silanes, or by reduction of 1,1-dihalosilane. It has long been assumed that the conversion of metallic Si to tetravalent silicon compounds proceeds via silylene intermediates: :Si + Cl2 → SiCl2 :SiCl2 + Cl2 → SiCl4 Similar considera ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element is therefore not a compound. A compound can be transformed into a different substance by a chemical reaction, which may involve interactions with other substances. In this process, bonds between atoms may be broken and/or new bonds formed. There are four major types of compounds, distinguished by how the constituent atoms are bonded together. Molecular compounds are held together by covalent bonds; ionic compounds are held together by ionic bonds; intermetallic compounds are held together by metallic bonds; coordination complexes are held together by coordinate covalent bonds. Non-stoichiometric compounds form a disputed marginal case. A chemical formula specifies the number of atoms of each element in a compound molecule, using the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Methyl Chloride
Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound with the chemical formula . One of the haloalkanes, it is a colorless, odorless, flammable gas. Methyl chloride is a crucial reagent in industrial chemistry, although it is rarely present in consumer products, and was formerly utilized as a refrigerant. Occurrence Chloromethane is an abundant organohalogen, anthropogenic or natural, in the atmosphere. Marine Laboratory cultures of marine phytoplankton (''Phaeodactylum tricornutum'', ''Phaeocystis'' sp., ''Thalassiosira weissflogii'', ''Chaetoceros calcitrans'', ''Isochrysis'' sp., ''Porphyridium'' sp., ''Synechococcus'' sp., ''Tetraselmis'' sp., ''Prorocentrum'' sp., and ''Emiliana huxleyi'') produce CH3Cl, but in relatively insignificant amounts. An extensive study of 30 species of polar macroalgae revealed the release of significant amounts of CH3Cl in only ''Gigartina skottsbergii'' and ''Gymnogongrus antarcticus''. Biogenesis T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a light, volatile, colourless, flammable liquid with a distinctive alcoholic odour similar to that of ethanol (potable alcohol). A polar solvent, methanol acquired the name wood alcohol because it was once produced chiefly by the destructive distillation of wood. Today, methanol is mainly produced industrially by hydrogenation of carbon monoxide. Methanol consists of a methyl group linked to a polar hydroxyl group. With more than 20 million tons produced annually, it is used as a precursor to other commodity chemicals, including formaldehyde, acetic acid, methyl tert-butyl ether, methyl benzoate, anisole, peroxyacids, as well as a host of more specialised chemicals. Occurrence Small amounts of methanol are present in normal, healthy hu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microsecond
A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is equal to 1000 nanoseconds or of a millisecond. Because the next SI prefix is 1000 times larger, measurements of 10−5 and 10−4 seconds are typically expressed as tens or hundreds of microseconds. Examples * 1 microsecond (1 μs) – cycle time for frequency (1 MHz), the inverse unit. This corresponds to radio wavelength 300 m (AM medium wave band), as can be calculated by multiplying 1 μs by the speed of light (approximately ). * 1 microsecond – the length of time of a high-speed, commercial strobe light flash (see air-gap flash). * 1 microsecond – protein folding takes place on the order of microseconds. * 1.8 microseconds – the amount of time subtracted from the Earth's day as a result of the 2011 Japanese earthquake. * 2 m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable atoms survive. The term is also used more generally to characterize any type of exponential decay, exponential (or, rarely, rate law, non-exponential) decay. For example, the medical sciences refer to the biological half-life of drugs and other chemicals in the human body. The converse of half-life (in exponential growth) is doubling time. The original term, ''half-life period'', dating to Ernest Rutherford's discovery of the principle in 1907, was shortened to ''half-life'' in the early 1950s. Rutherford applied the principle of a radioactive chemical element, element's half-life in studies of age determination of rocks by measuring the decay period of radium to lead-206. Half-life is constant over the lifetime of an exponentially decaying ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
UV Spectroscopy
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules. Short-wave ultraviolet light damages DNA and sterilizes surfaces with which it comes into contact. For huma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flash Photolysis
Flash photolysis is a pump-probe laboratory technique, in which a sample is first excited by a strong pulse of light from a pulsed laser of nanosecond, picosecond, or femtosecond pulse width or by another short-pulse light source such as a flash lamp. This first strong pulse is called the pump pulse and starts a chemical reaction or leads to an increased population for energy levels other than the ground state within a sample of atoms or molecules. Typically the absorption of light by the sample is recorded within short time intervals (by a so-called test or probe pulses) to monitor relaxation or reaction processes initiated by the pump pulse. Flash photolysis was developed shortly after World War II as an outgrowth of attempts by military scientists to build cameras fast enough to photograph missiles in flight. The technique was developed in 1949 by Manfred Eigen, Ronald George Wreyford Norrish and George Porter, who won the 1967 Nobel Prize in Chemistry for this invention. O ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decamethylsilicocene
Decamethylsilicocene, (C5Me5)2Si, is a group 14 sandwich compound. It is an example of a main-group cyclopentadienyl complex; these molecules are related to metallocenes but contain p-block elements as the central atom. It is a colorless, air sensitive solid that sublimes under vacuum. Synthesis The first synthesis of decamethylsilicocene was reported by Jutzi and coworkers in 1986. It involved reduction of bis(pentamethylcyclopentadienyl)silicon(IV) dichloride with two equivalents of sodium naphthalenide to generate decamethylsilicocene, naphthalene, and sodium chloride. Generation of the sterically crowded bis(pentamethylcyclopentadienyl)silicon(IV) dichloride required several steps, beginning with double deprotonation of (C5Me4H)2SiCl2 using ''tert''-butyllithium, followed by treatment of the resultant (C5Me4Li)2SiCl2 with methyl iodide. Decamethylsilicocene is soluble in aprotic solvents such as hexane, benzene, and chlorinated solvents. Molecular weight determinations sho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Michael K
''Life & Times of Michael K'' is a 1983 novel by South African-born writer J. M. Coetzee. The novel won the Booker Prize for 1983. The novel is a story of a man named Michael K, who makes an arduous journey from Cape Town to his mother's rural birthplace, amid a fictitious civil war during the apartheid era, in the 1970-80s. Plot summary The novel is split into three parts. The novel begins with Michael K, a poor man with a cleft lip who has spent his childhood in institutions and works as a gardener in Cape Town. Michael tends to his mother who works as a domestic servant to a wealthy family. The country descends into civil war and martial law is imposed, and Michael's mother becomes very sick. Michael decides to quit his job and escape the city to return his mother to her birthplace, which she says was Prince Albert. Michael finds himself unable to obtain the proper permits for travel out of the city so he builds a shoddy rickshaw to carry his mother, and they go on their ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
N-heterocyclic Silylene
An ''N''-Heterocyclic silylene (NHSi) is an uncharged Heterocyclic compound, heterocyclic Chemical compounds, chemical compound consisting of a Silylene, divalent silicon atom bonded to two nitrogen atoms. The isolation of the first stable NHSi, also the first stable dicoordinate silicon compound, was reported in 1994 by Michael Denk and Robert West (chemist), Robert West three years after Anthony Joseph Arduengo III, Anthony Arduengo first isolated an N-heterocyclic carbene, the lighter Congener (chemistry), congener of NHSis. Since their first isolation, NHSis have been synthesized and studied with both saturated and unsaturated central rings ranging in size from 4 to 6 atoms. The stability of NHSis, especially 6π aromatic unsaturated five-membered examples, make them useful systems to study the structure and reactivity of silylenes and low-valent main group elements in general. Though not used outside of academic settings, complexes containing NHSis are known to be competent ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
