|
Electrophilic Substitution Of Unsaturated Silanes
Electrophilic substitution of unsaturated silanes involves attack of an electrophile on an Allyl group, allyl- or vinylsilane. An allyl or vinyl group is incorporated at the electrophilic center after loss of the silyl group. Introduction In 1948, it was discovered that allyltrimethylsilane reacts with hydrobromic acid to give (2-bromopropyl)trimethylsilane. Six years later, the generation of (2-iodoethyl)trimethylsilane from vinylsilane and HI was observed. Since then, a number of studies have firmly established the mechanism of electrophilic attack on vinyl- and allylsilanes The electron-releasing strength of the carbon-silicon bond is large, and as a result, the position of silicon in the unsaturated silane controls the site of reaction and stereoselectivity. Formation of the new carbon-carbon bond is at the γ position of allyl silanes and the β position of vinylsilanes. The robustness of silanes makes them amenable to use in synthesis; however, because silicon is less electropo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrophile
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively Electric charge, charged, have an atom that carries a partial positive charge, or have an atom that does not have an octet of electrons. Electrophiles mainly interact with nucleophiles through Addition reaction, addition and Substitution reaction, substitution reactions. Frequently seen electrophiles in Organic synthesis, organic syntheses include cations such as Hydrogen ion, H+ and nitrosonium, NO+, polarized neutral molecules such as hydrogen chloride, HCl, alkyl halides, acyl halides, and carbonyl compounds, polarizable neutral molecules such as chlorine, Cl2 and bromine, Br2, oxidizing agents such as organic peracids, chemical species that do not satisfy the octet rule such as carbenes and Radical (chemistry), radicals, and some Lewis acids such as Borane, BH3 and Di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleophilic Catalysis
Enzyme catalysis is the increase in the rate of a process by an "enzyme", a biological molecule. Most enzymes are proteins, and most such processes are chemical reactions. Within the enzyme, generally catalysis occurs at a localized site, called the active site. Most enzymes are made predominantly of proteins, either a single protein chain or many such chains in a multi-subunit complex. Enzymes often also incorporate non-protein components, such as metal ions or specialized organic molecules known as cofactor (e.g. adenosine triphosphate). Many cofactors are vitamins, and their role as vitamins is directly linked to their use in the catalysis of biological process within metabolism. Catalysis of biochemical reactions in the cell is vital since many but not all metabolically essential reactions have very low rates when uncatalysed. One driver of protein evolution is the optimization of such catalytic activities, although only the most crucial enzymes operate near catalytic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diastereomer
In stereochemistry, diastereomers (sometimes called diastereoisomers) are a type of stereoisomer. Diastereomers are defined as non-mirror image, non-identical stereoisomers. Hence, they occur when two or more stereoisomers of a compound have different configurations at one or more (but not all) of the equivalent (related) stereocenters and are not mirror images of each other. When two diastereoisomers differ from each other at only one stereocenter, they are epimers. Each stereocenter gives rise to two different configurations and thus typically increases the number of stereoisomers by a factor of two. Diastereomers differ from enantiomers in that the latter are pairs of stereoisomers that differ in all stereocenters and are therefore mirror images of one another. Enantiomers of a compound with more than one stereocenter are also diastereomers of the other stereoisomers of that compound that are not their mirror image (that is, excluding the opposing enantiomer). Diastereomers ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Titanium Tetrachloride
Titanium tetrachloride is the inorganic compound with the formula . It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. is a volatile liquid. Upon contact with humid air, it forms thick clouds of titanium dioxide () and hydrochloric acid, a reaction that was formerly exploited for use in smoke machines. It is sometimes referred to as "tickle" or "tickle 4", as a phonetic representation of the symbols of its molecular formula (). Properties and structure is a dense, colourless liquid, although crude samples may be yellow or even red-brown. It is one of the rare transition metal halides that is a liquid at room temperature, being another example. This property reflects the fact that molecules of weakly self-associate. Most metal chlorides are polymers, wherein the chloride atoms bridge between the metals. Its melting point is similar to that of . has a "closed" electronic shell, with the same number of electrons as the nobl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epoxidation
In organic chemistry, an epoxide is a cyclic ether, where the ether forms a three-atom ring: two atoms of carbon and one atom of oxygen. This triangular structure has substantial ring strain, making epoxides highly reactive, more so than other ethers. They are produced on a large scale for many applications. In general, low molecular weight epoxides are colourless and nonpolar, and often volatile. Nomenclature A compound containing the epoxide functional group can be called an epoxy, epoxide, oxirane, and ethoxyline. Simple epoxides are often referred to as oxides. Thus, the epoxide of ethylene (C2H4) is ethylene oxide (C2H4O). Many compounds have trivial names; for instance, ethylene oxide is called "oxirane". Some names emphasize the presence of the epoxide functional group, as in the compound ''1,2-epoxyheptane'', which can also be called ''1,2-heptene oxide''. A polymer formed from epoxide precursors is called an ''epoxy''. However, few if any of the epoxy groups in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbonyl Group
In organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such as aldehydes, ketones and carboxylic acid), as part of many larger functional groups. A compound containing a carbonyl group is often referred to as a carbonyl compound. The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex (a metal carbonyl, e.g. nickel carbonyl). The remainder of this article concerns itself with the organic chemistry definition of carbonyl, such that carbon and oxygen share a double bond. Carbonyl compounds In organic chemistry, a carbonyl group characterizes the following types of compounds: Other organic carbonyls are urea and the carbamates, the derivatives of acyl chlorides, chloroformates and phosgene, carbonate esters, thioesters, lactones, lactams, hydroxama ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Halide
In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluoride, chloride, bromide, iodide, astatide, or theoretically tennesside compound. The alkali metals combine directly with halogens under appropriate conditions forming halides of the general formula, MX (X = F, Cl, Br or I). Many salts are halides; the ''hal-'' syllable in ''halide'' and '' halite'' reflects this correlation. A halide ion is a halogen atom bearing a negative charge. The common halide anions are fluoride (), chloride (), bromide (), and iodide (). Such ions are present in many ionic halide salts. Halide minerals contain halides. All these halide anions are colorless. Halides also form covalent bonds, examples being colorless TiF4, colorless TiCl4, orange TiBr4, and brown TiI4. The heavier members TiCl4, TiBr4 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stoichiometric
Stoichiometry () is the relationships between the masses of reactants and products before, during, and following chemical reactions. Stoichiometry is based on the law of conservation of mass; the total mass of reactants must equal the total mass of products, so the relationship between reactants and products must form a ratio of positive integers. This means that if the amounts of the separate reactants are known, then the amount of the product can be calculated. Conversely, if one reactant has a known quantity and the quantity of the products can be empirically determined, then the amount of the other reactants can also be calculated. This is illustrated in the image here, where the unbalanced equation is: : : However, the current equation is imbalanced. The reactants have 4 hydrogen and 2 oxygen atoms, while the product has 2 hydrogen and 3 oxygen. To balance the hydrogen, a coefficient of 2 is added to the product H2O, and to fix the imbalance of oxygen, it is also added ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isomer
In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the existence or possibility of isomers. Isomers do not necessarily share similar chemical property, chemical or physical property, physical properties. Two main forms of isomerism are structural isomerism, structural (or constitutional) isomerism, in which ''chemical bond, bonds'' between the atoms differ; and stereoisomerism (or spatial isomerism), in which the bonds are the same but the ''relative positions'' of the atoms differ. Isomeric relationships form a hierarchy. Two chemicals might be the same constitutional isomer, but upon deeper analysis be stereoisomers of each other. Two molecules that are the same stereoisomer as each other might be in different conformational forms or be different Isotopologue, isotopologues. The depth of analy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
