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Xylylene
In organic chemistry, a xylylene (sometimes quinone-dimethide) is any of the constitutional isomers having the formula C6H4(CH2)2. These compounds are related to the corresponding quinones and quinone methides by replacement of the oxygen atoms by CH2 groups. ''ortho''- and ''para''-xylylene are best known, although neither is stable in solid or liquid form. The ''meta'' form is a diradical. Certain substituted derivatives of xylylenes are however highly stable, such as tetracyanoquinodimethane and the xylylene dichlorides. p-Xylylene ''p''-Xylylene forms upon pyrolysis of ''p''-xylene or, more readily, the α-substituted derivatives. ''p''-Xylylene dimerizes with moderate efficiency to give ''p''-cyclophane: Further heating of the ''p''-cyclophane gives poly(''para''-xylylene). o-Xylylenes o-Xylylenes (''o''-quinodimethanes) are often generated in situ, e.g., by the pyrolysis of the corresponding sulfone. Another method involves 1,4-elimination of ortho benzylic silanes. ...
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O-xylylene
In organic chemistry, a xylylene (sometimes quinone-dimethide) is any of the constitutional isomers having the formula C6H4(CH2)2. These compounds are related to the corresponding quinones and quinone methides by replacement of the oxygen atoms by CH2 groups. ''ortho''- and ''para''-xylylene are best known, although neither is stable in solid or liquid form. The ''meta'' form is a diradical. Certain substituted derivatives of xylylenes are however highly stable, such as tetracyanoquinodimethane and the xylylene dichlorides. p-Xylylene ''p''-Xylylene forms upon pyrolysis of ''p''-xylene or, more readily, the α-substituted derivatives. ''p''-Xylylene dimerizes with moderate efficiency to give ''p''-cyclophane: Further heating of the ''p''-cyclophane gives poly(''para''-xylylene). o-Xylylenes o-Xylylenes (''o''-quinodimethanes) are often generated in situ, e.g., by the pyrolysis of the corresponding sulfone. Another method involves 1,4-elimination of ortho benzylic silanes. ...
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Xylylene Dichloride
The chemical compound xylylene dichloride (C6H4(CH2Cl)2) is a white to light yellow sandlike solid. This compound can be classified as a benzyl halide. Xylylene dichloride is used as a vulcanizing agent to harden rubbers. It catalyzes the crosslinking of phenolic resins. Structure and reactivity The structure of xylylene dichloride is characterized by an benzene ring with two chloromethyl groups and four hydrogen atoms bound to it. The chloromethyl groups can be located on different sites on the ring, leading to a few different possible forms. These forms are: *''o''-xylylene dichloride: 1,2-bis(chloromethyl)benzene *''m''-xylylene dichloride: 1,3-bis(chloromethyl)benzene *''p''-xylylene dichloride: 1,4-bis(chloromethyl)benzene The reactive groups of xylylene dichloride are the two CH2Cl groups. Synthesis Xylylene dichloride can be synthesized from benzenedimethanol by reaction with hydrogen chloride. It has also been produced by photochemical chlorination of ortho-xylene ...
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Quinone
The quinones are a class of organic compounds that are formally "derived from aromatic compounds [such as benzene or naphthalene] by conversion of an even number of –CH= groups into –C(=O)– groups with any necessary rearrangement of double bonds, resulting in "a fully Conjugated system, conjugated cyclic diketone, dione structure". The archetypical member of the class is 1,4-benzoquinone or cyclohexadienedione, often called simply "quinone" (thus the name of the class). Other important examples are 1,2-benzoquinone (''ortho''-quinone), 1,4-naphthoquinone and anthraquinone, 9,10-anthraquinone. The name is derived from that of quinic acid (with the suffix "-one" indicating a ketone), since it is one of the compounds obtained upon oxidation of quinic acid. Quinic acid, like quinine is obtained from cinchona bark, called wikt:quinaquina, quinaquina in the indigenous languages of Peruvian tribes. Properties Quinones are oxidized derivatives of aromatic compounds and are often re ...
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Benzocyclobutene
Benzocyclobutene (BCB) is a benzene ring fused to a cyclobutane ring. It has chemical formula . BCB is frequently used to create photosensitive polymers. BCB-based polymer dielectrics may be spun on or applied to various Wafer (electronics), substrates for use in Micro Electro-Mechanical Systems (MEMS) and microelectronics processing. Applications include wafer bonding, optical interconnects, low-κ dielectrics, or even intracortical neural implants. Reactions Benzocyclobutene is a strained system which, upon heating to approximately 180 °C, causes the cyclobutene to undergo a conrotatory Cyclic_compound#Ring-opening_reactions, ring-opening reaction, forming o-xylylene, ''o''-xylylene. Since this process destroys the aromaticity of the benzene ring, the reverse reaction is highly favored. ''o''-Xylylenes generated in this way have been used prolifically in cycloaddition reactions, which restore the aromaticity to the benzene ring, while forming a new annulation, annulated ...
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Tetrabromo-o-xylene
α,α,α',α'-Tetrabromo-o-xylene is an organobromine compound with the formula C6H4(CHBr2)2. Three isomers of α,α,α',α'-Tetrabromoxylene exist, but the ortho derivative is most widely studied. It is an off-white solid. The compound is prepared by the photochemical reaction of o-xylene with elemental bromine: : Reaction of α,α,α',α'-tetrabromo-o-xylene with sodium iodide affords α,α'-dibromo-o-xylylene, which can be trapped with dienophiles to give naphthylene. In the absence of trapping agents, the xylylene relaxes to α,α'-dibromobenzocyclobutane: : : Cycloadditions of these xylylenes provides a pathway to acene In organic chemistry, the acenes or polyacenes are a class of organic compounds and polycyclic aromatic hydrocarbons made up of benzene () rings which have been linearly fused. They follow the general molecular formula . The larger representa ...s.{{cite journal , doi=10.1055/s-1986-31603, title=An Efficient Synthetic Strategy for Naphthalene Annel ...
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Superphane
.2.2.2.2.21,2,3,4,5,6)Cyclophane or superphane is a 6-fold bridged cyclophane with all arene positions in the benzene dimer taken up by ethylene spacers. The compound has been of some scientific interest as a model for testing aromaticity and was first synthesised by Virgil Boekelheide in 1979. Superphane is the base compound for a large group of derivatives with structural variations. The analogs with 2 to 5 bridges are also known compounds. The benzene rings have been replaced by other aromatic units, such as those based on ferrocene or stabilized cyclobutadiene. Numerous derivatives are known with variations in the type and length of the bridging units. Synthesis The first synthesis of superphane itself by Boekelheide involved forming pairs of bridging units. At each stage, two ''o''-chloromethyl toluene structures are pyrolyzed to form ''o''-xylylenes, either directly or via benzocyclobutene intermediates. Upon further pyrolysis, these each undergo electrocyclic ring-opening ...
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Cycloaddition
In organic chemistry, a cycloaddition is a chemical reaction in which "two or more Unsaturated hydrocarbon, unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of the Multiplicity (chemistry)#Molecules, bond multiplicity". The resulting reaction is a cyclization reaction. Many but not all cycloadditions are Concerted reaction, concerted and thus pericyclic. Nonconcerted cycloadditions are not pericyclic. As a class of addition reaction, cycloadditions permit carbon–carbon bond formation without the use of a nucleophile or electrophile. Cycloadditions can be described using two systems of notation. An older but still common notation is based on the size of linear arrangements of atoms in the reactants. It uses parentheses: where the variables are the numbers of linear atoms in each reactant. The product is a cycle of size . In this system, the standard Diels-Alder reaction is a (4 + 2)-cyc ...
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Electrocyclic Reaction
In organic chemistry, an electrocyclic reaction is a type of pericyclic rearrangement where the net result is one pi bond being converted into one sigma bond or vice versa. These reactions are usually categorized by the following criteria: * Reactions can be either photochemical or thermal. * Reactions can be either ring-opening or ring-closing (electrocyclization). * Depending on the type of reaction (photochemical or thermal) and the number of pi electrons, the reaction can happen through either a conrotatory or disrotatory mechanism. * The type of rotation determines whether the cis or trans isomer of the product will be formed. Classical examples The Nazarov cyclization reaction is a named electrocyclic reaction converting divinylketones to cyclopentenones. A classic example is the thermal ring-opening reaction of 3,4-dimethylcyclobutene. The cis isomer exclusively yields whereas the trans isomer gives the trans,trans diene: This reaction course can be explained in a sim ...
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1,3-butadiene
1,3-Butadiene () is the organic compound with the formula (CH2=CH)2. It is a colorless gas that is easily condensed to a liquid. It is important industrially as a precursor to synthetic rubber. The molecule can be viewed as the union of two vinyl groups. It is the simplest conjugated diene. Although butadiene breaks down quickly in the atmosphere, it is nevertheless found in ambient air in urban and suburban areas as a consequence of its constant emission from motor vehicles. The name butadiene can also refer to the isomer, 1,2-butadiene, which is a cumulated diene with structure H2C=C=CH−CH3. This allene has no industrial significance. History In 1863, the French chemist E. Caventou isolated butadiene from the pyrolysis of amyl alcohol. This hydrocarbon was identified as butadiene in 1886, after Henry Edward Armstrong isolated it from among the pyrolysis products of petroleum. In 1910, the Russian chemist Sergei Lebedev polymerized butadiene and obtained a material wit ...
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Iron Carbonyl
Iron pentacarbonyl, also known as iron carbonyl, is the compound with formula . Under standard conditions Fe( CO)5 is a free-flowing, straw-colored liquid with a pungent odour. Older samples appear darker. This compound is a common precursor to diverse iron compounds, including many that are useful in small scale organic synthesis. Properties Iron pentacarbonyl is a homoleptic metal carbonyl, where carbon monoxide is the only ligand complexed with a metal. Other examples include octahedral Cr(CO)6 and tetrahedral Ni(CO)4. Most metal carbonyls have 18 valence electrons, and Fe(CO)5 fits this pattern with 8 valence electrons on Fe and five pairs of electrons provided by the CO ligands. Reflecting its symmetrical structure and charge neutrality, Fe(CO)5 is volatile; it is one of the most frequently encountered liquid metal complexes. Fe(CO)5 adopts a trigonal bipyramidal structure with the Fe atom surrounded by five CO ligands: three in equatorial positions and two axially b ...
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Coordination Complex
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many metal-containing compounds, especially those that include transition metals (elements like titanium that belong to the Periodic Table's d-block), are coordination complexes. Nomenclature and terminology Coordination complexes are so pervasive that their structures and reactions are described in many ways, sometimes confusingly. The atom within a ligand that is bonded to the central metal atom or ion is called the donor atom. In a typical complex, a metal ion is bonded to several donor atoms, which can be the same or different. A polydentate (multiple bonded) ligand is a molecule or ion that bonds to the central atom through several of the ligand's atoms; ligands with 2, 3, 4 or even 6 bonds to the central atom are common. These compl ...
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Ligand (chemistry)
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs, often through Lewis bases. The nature of metal–ligand bonding can range from covalent to ionic. Furthermore, the metal–ligand bond order can range from one to three. Ligands are viewed as Lewis bases, although rare cases are known to involve Lewis acidic "ligands". Metals and metalloids are bound to ligands in almost all circumstances, although gaseous "naked" metal ions can be generated in a high vacuum. Ligands in a complex dictate the reactivity of the central atom, including ligand substitution rates, the reactivity of the ligands themselves, and redox. Ligand selection requires critical consideration in many practical areas, including bioinorganic and medicinal chemistry, homogeneous catalysis, and environmental chemist ...
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