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Dimesityldioxirane
Dimesityldioxirane is a substituted dioxirane with two mesityl groups attached to the dioxirane carbon. It is a colorless crystalline substance stable in its solid state around -20 °C. Structure The molecule possesses approximately C2 symmetry and the mesityl groups are twisted by 54.2°. The bulky mesityl groups cause steric strain which is reduced by increase in R1–C–R2 angle from 117° in dioxirane to 119.2° in dimesityldioxirane. The mesityl groups also rotate about the single bond, consequently reducing steric repulsions further. Synthesis and Uses Dimesityldioxirane was first isolated at room temperature in pure as well as in solution form in 1994. It was synthesised by irradiation of its diazo derivative in trichlorofluoromethane at 183K to form , followed by oxidation. The synthesis had a yield of 50%. It can mainly be used as an oxidizing agent but is less oxidizing than other dioxiranes due to its stability. See also * Difluorodioxirane *Dimethyldioxir ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dioxirane
In chemistry, dioxirane (systematically named dioxacyclopropane, also known as methylene peroxide or peroxymethane) is an organic compound with formula . The molecule consists of a ring with one methylene and two oxygen atoms. It is of interest as the smallest cyclic organic peroxide, but otherwise it is of little practical value. Synthesis Dioxirane is highly unstable and the majority of studies of it have been computational; it has been detected during the low temperature (–196 °C) reaction of ethylene and ozone, although even at these temperatures such a mixture can be explosive. Its formation is thought to be radical in nature, preceding via a Criegee intermediate. Microwave analysis has indicated C-H, C-O and O-O bond lengths of 1.090, 1.388 and 1.516 Å respectively. The very long and weak O-O bond (cf. hydrogen peroxide O-O = 1.47 Å) is the origin of its instability. Other dioxiranes Beyond the parent dioxirane, which is mainly of theoretical interest, more c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Difluorodioxirane
Difluorodioxirane (CF2O2) is a rare, stable member of the dioxirane family, known for a single oxygen-oxygen bond (O-O). Unlike most dioxiranes that decompose quickly, difluorodioxirane is surprisingly stable at room temperature, making it potentially useful for further research and applications. Synthesis Difluorodioxirane was first synthesised by Russo and DesMarteau in 1993 by treating fluorocarbonyl hypofluorite (FCOOF) with X2 (= F2, Cl2 or ClF) over pelletized CsF in a flow system. It also likely exists as a possible intermediate in reactions involving other fluorine-containing compounds. Properties Unlike most dioxiranes that decompose quickly, difluorodioxirane is surprisingly stable at room temperature due to the stabilising interacton of two fluorine atoms with the ring. This effect makes the O-O bond less reactive and more stable compared to other dioxiranes. The central F–C–F angle is 109°, approximately a tetrahedral angle. Difluorodioxirane is known fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dioxiranes
In chemistry, dioxirane (systematically named dioxacyclopropane, also known as methylene peroxide or peroxymethane) is an organic compound with formula . The molecule consists of a ring with one Methylene group, methylene and two oxygen atoms. It is of interest as the smallest cyclic organic peroxide, but otherwise it is of little practical value. Synthesis Dioxirane is highly unstable and the majority of studies of it have been computational chemistry, computational; it has been detected during the low temperature (–196 °C) reaction of ethylene and ozone, although even at these temperatures such a mixture can be explosive. Its formation is thought to be radical in nature, preceding via a Criegee intermediate. Microwave analysis has indicated C-H, C-O and O-O bond lengths of 1.090, 1.388 and 1.516 Å respectively. The very long and weak O-O bond (cf. hydrogen peroxide O-O = 1.47 Å) is the origin of its instability. Other dioxiranes Beyond the parent dioxirane, which i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mesitylene
Mesitylene or 1,3,5-trimethylbenzene is a derivative of benzene with three methyl substituents positioned symmetrically around the ring. The other two isomeric trimethylbenzenes are 1,2,4-trimethylbenzene (pseudocumene) and 1,2,3-trimethylbenzene (hemimellitene). All three compounds have the formula C6H3(CH3)3, which is commonly abbreviated C6H3Me3. Mesitylene is a colorless liquid with sweet aromatic odor. It is a component of coal tar, which is its traditional source. It is a precursor to diverse fine chemicals. The mesityl group (Mes) is a substituent with the formula C6H2Me3 and is found in various other compounds. Preparation Mesitylene is prepared by transalkylation of xylene over solid acid catalyst:Karl Griesbaum, Arno Behr, Dieter Biedenkapp, Heinz-Werner Voges, Dorothea Garbe, Christian Paetz, Gerd Collin, Dieter Mayer, Hartmut Höke “Hydrocarbons” in Ullmann's Encyclopedia of Industrial Chemistry 2002 Wiley-VCH, Weinheim. . :2 C6H4(CH3)2 ⇌ C6H ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C2-Symmetric Ligands
In homogeneous catalysis, ''C''2-symmetric ligands refer to ligands that lack mirror symmetry but have ''C''2 symmetry (two-fold rotational symmetry). Such ligands are usually bidentate and are valuable in catalysis. The ''C''2 symmetry of ligands limits the number of possible reaction pathways and thereby increases enantioselectivity, relative to asymmetrical analogues. ''C''2-symmetric ligands are a subset of chiral ligands. Chiral ligands, including ''C''2-symmetric ligands, combine with metals or other groups to form chiral catalysts. These catalysts engage in enantioselective chemical synthesis, in which chirality in the catalyst yields chirality in the reaction product. Examples An early ''C''2-symmetric ligand, diphosphine catalytic ligand DIPAMP, was developed in 1968 by William S. Knowles and coworkers of Monsanto Company, who shared the 2001 Nobel Prize in Chemistry. This ligand was used in the industrial production of -DOPA. : Some classes of ''C''2-symmetric li ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Steric Effects
Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is generally a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape (conformational isomerism, conformation) and chemical reaction, reactivity of ions and molecules. Steric effects complement electronic effects, which dictate the shape and reactivity of molecules. Steric repulsive forces between overlapping electron clouds result in structured groupings of molecules stabilized by the way that opposites attract and like charges repel. Steric hindrance Steric hindrance is a consequence of steric effects. Steric hindrance is the slowing of chemical reactions due to steric bulk. It is usually manifested in ''intermolecular reactions'', whereas discussion of steric effects often focus on ''intramolecular interactions''. Steric hindrance is often exploited to control selectivity, such as slowing unwanted side-reactions. Steric hindran ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diazo
In organic chemistry, the diazo group is an organic moiety consisting of two linked nitrogen atoms at the terminal position. Overall charge-neutral organic compounds containing the diazo group bound to a carbon atom are called diazo compounds or diazoalkanes and are described by the general structural formula . The simplest example of a diazo compound is diazomethane, . Diazo compounds () should not be confused with azo compounds () or with diazonium compounds (). Structure The electronic structure of diazo compounds is characterized by π electron density delocalized over the α-carbon and two nitrogen atoms, along with an orthogonal π system with electron density delocalized over only the terminal nitrogen atoms. Because all octet rule-satisfying resonance forms of diazo compounds have formal charges, they are members of a class of compounds known as 1,3-dipoles. Some of the most stable diazo compounds are α-diazo-β-diketones and α-diazo-β-diesters, in which the e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trichlorofluoromethane
Trichlorofluoromethane, also called freon-11, CFC-11, or R-11, is a chlorofluorocarbon (CFC). It is a colorless, faintly ethereal, and sweetish-smelling liquid that boils around room temperature. CFC-11 is a Class 1 ozone-depleting substance which damages Earth's protective stratospheric ozone layer. R-11 is not flammable at ambient temperature and pressure but it can become very combustible if heated and ignited by a strong ignition source. Historical use Trichlorofluoromethane was first widely used as a refrigerant. Because of its high boiling point compared to most refrigerants, it can be used in systems with a low operating pressure, making the mechanical design of such systems less demanding than that of higher-pressure refrigerants R-12 or R-22. Trichlorofluoromethane is used as a reference compound for fluorine-19 NMR studies. Trichlorofluoromethane was formerly used in the drinking bird novelty, largely because it has a boiling point of . The replacement, di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxidizing Agent
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ''electron donor''). In other words, an oxidizer is any substance that oxidizes another substance. The oxidation state, which describes the degree of loss of electrons, of the oxidizer decreases while that of the reductant increases; this is expressed by saying that oxidizers "undergo reduction" and "are reduced" while reducers "undergo oxidation" and "are oxidized". Common oxidizing agents are oxygen, hydrogen peroxide, and the halogens. In one sense, an oxidizing agent is a chemical species that undergoes a chemical reaction in which it gains one or more electrons. In that sense, it is one component in an oxidation–reduction (redox) reaction. In the second sense, an oxidizing agent is a chemical species that transfers electronegative atoms, usually oxygen, t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dimethyldioxirane
Dimethyldioxirane (DMDO) is the organic compound with the formula . It is the dioxirane derived from acetone and can be viewed as the monomer of acetone peroxide. It is a powerful selective oxidizing agent that finds some use in organic synthesis. It is known only in the form of a dilute solution, usually in acetone, and hence the properties of the pure material are largely unknown. Synthesis DMDO is not commercially available because of chemical instability. DMDO can be prepared as dilute solutions (~0.1 M) by treatment of acetone with potassium peroxymonosulfate , usually in the form of Oxone (2KHSO5·KHSO4·K2SO4). : The preparation of DMDO is rather inefficient (typical yields < 3%) and typically only yields a relatively dilute solution in acetone (only up to approximately 0.1 M). This is tolerable as preparation uses inexpensive substances: acetone, sodium bicarbonate, and oxone. Cold solutions (−10 to −20 °C) of DMDO are stable for days. Decomposition is accelerat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shi Epoxidation
The Shi epoxidation is a chemical reaction described as the asymmetric epoxidation of alkenes with oxone (potassium peroxymonosulfate) and a fructose-derived catalyst (1). This reaction is thought to proceed via a dioxirane intermediate, generated from the catalyst ketone by oxone (potassium peroxymonosulfate). The addition of the sulfate group by the oxone facilitates the formation of the dioxirane by acting as a good leaving group during ring closure. It is notable for its use of a non-metal catalyst and represents an early example of organocatalysis. History The reaction was first reported by Yian Shi (史一安, pinyin: Shǐ Yī-ān) is derived from D-fructose and has a stereogenic center close to the reacting center (ketone)- the rigid six-membered ring structure of the catalyst and adjacent quaternary ring group minimizes epimerization of this stereocenter. Oxidation by the active dioxirane catalyst takes place from the si-face, due to steric hindrance of the opposing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organic Peroxides
In organic chemistry, organic peroxides are organic compounds containing the peroxide functional group (). If the R′ is hydrogen, the compounds are called hydroperoxides, which are discussed in that article. The O−O bond of peroxides easily breaks, producing free radicals of the form (the dot represents an unpaired electron). Thus, organic peroxides are useful as radical initiator, initiators for some types of polymerization, such as the Acrylic resin, acrylic, unsaturated polyester, and vinyl ester resins used in glass-reinforced plastics. methyl ethyl ketone peroxide, MEKP and benzoyl peroxide are commonly used for this purpose. However, the same property also means that organic peroxides can explosively combust. Organic peroxides, like their inorganic counterparts, are often powerful bleaching agents. Types of organic peroxides Organic peroxides are classified (i) by the presence or absence of a hydroxyl () terminus and (ii) by the presence of alkyl vs acyl substituents. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
