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Organotellurium
Organotellurium chemistry describes the synthesis and properties of chemical compounds containing a carbon-tellurium chemical bond. Organotellurium chemistry is a lightly studied area, in part because of the few applications. Functional groups The Te analogues of common organosulfur and organoselenium functional groups are known. Tellurols are however unstable with respect to oxidation to the ditellurides. Commonly encountered organotellurium compounds are diorganomono- and ditellurides, R2Te and (RTe)2, respectively. Two other families of organoTe(IV) compounds are well developed: R4−xTeClx and the telluroxides (R2TeO). Synthesis and reactions Reduced organoTe compounds Reduced organoTe compounds are commonly obtained from NaHTe and lithium telluride: :Li2Te + 2 RBr → R2Te + 2 LiBr A direct route to organolithium compounds starts from reactions of organolithium or Grignard reagents and Te: :Te + ArLi → ArTeLi Butyl lithium gives the telluride similarly: :Te + B ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tellurium
Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally found in native form as elemental crystals. Tellurium is far more common in the Universe as a whole than on Earth. Its extreme rarity in the Earth's crust, comparable to that of platinum, is due partly to its formation of a volatile hydride that caused tellurium to be lost to space as a gas during the hot nebular formation of Earth.Anderson, Don L.; "Chemical Composition of the Mantle" in ''Theory of the Earth'', pp. 147-175 Tellurium-bearing compounds were first discovered in 1782 in a gold mine in Kleinschlatten, Transylvania (now Zlatna, Romania) by Austrian mineralogist Franz-Joseph Müller von Reichenstein, although it was Martin Heinrich Klaproth who named the new element in 1798 after the Latin 'earth'. Gold telluride minerals ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organoselenium Compound
Organoselenium compounds (or seleno-organic) are chemical compounds containing carbon-to-selenium chemical bonds. Organoselenium chemistry is the corresponding science exploring their properties and reactivity. Selenium belongs with oxygen and sulfur to the group 16 elements or chalcogens, and similarities in chemistry are to be expected. Organoselenium compounds are found at trace levels in ambient waters, soils and sediments. Selenium can exist with oxidation state −2, +2, +4, +6. Se(II) is the dominant form in organoselenium chemistry. Down the group 16 column, the bond strength becomes increasingly weaker (234 kJ/ mol for the C−Se bond and 272 kJ/mol for the C−S bond) and the bond lengths longer (C−Se 198 pm, C−S 181 pm and C−O 141 pm). Selenium compounds are more nucleophilic than the corresponding sulfur compounds and also more acidic. The p''K''a values of XH2 are 16 for oxygen, 7 for sulfur and 3.8 for selenium. In contrast to sulfoxides, the corresponding sel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tellurol
Tellurols are analogues of alcohols and phenols where tellurium replaces oxygen. Tellurols, selenols, and thiols have similar properties, but tellurols are the least stable. Although they are fundamental representatives of organotellurium compounds, tellurols are lightly studied because of their instability. Tellurol derivatives include telluroesters (RC(O)TeR') and tellurocyanates (RTeCN). Properties Alkyltellurols are colorless liquids with strong odors. Samples usually appear yellowish owing to the presence of dialkylditelluride impurities. Near room temperature, methanetellurol degrades with loss of elemental tellurium. It is reported to ignite in air. Aryltellurols are more robust and have been obtained as colorless crystals. Some of the most stable tellurols are the bulky silylated derivatives of tris(trimethylsilyl)methane and analogues. One series of readily isolable tellurols is , , and . Acid–base properties The acidity of tellurols can be inferred by the acidity ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telluroxide
A telluroxide is a type of organotellurium compound with the formula R2TeO. These compounds are analogous to sulfoxides in some respects. Reflecting the decreased tendency of Te to form multiple bonds, telluroxides exist both the monomer and the 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 a ..., which are favored in solution and the solid state, respectively:Jens Beckmann, Dainis Dakternieks, Andrew Duthie, François Ribot, Markus Schürmann, and Naomi A. Lewcenko "New Insights into the "Structures of Diorganotellurium Oxides. The First Polymeric Diorganotelluroxane p-MeOC6H4)2TeOsub>n" Organometallics, 2003, volume 22, 3257–3261. :(R2TeO)n {{Eqm n R2TeO Telluroxides are prepared from the telluroethers by halogenation followed by base hydrolysis: :R2Te + Br2 → ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Selenoxide Oxidation
Organoselenium compounds (or seleno-organic) are chemical compounds containing carbon-to-selenium chemical bonds. Organoselenium chemistry is the corresponding science exploring their properties and reactivity. Selenium belongs with oxygen and sulfur to the group 16 elements or chalcogens, and similarities in chemistry are to be expected. Organoselenium compounds are found at trace levels in ambient waters, soils and sediments. Selenium can exist with oxidation state −2, +2, +4, +6. Se(II) is the dominant form in organoselenium chemistry. Down the group 16 column, the bond strength becomes increasingly weaker (234 kJ/ mol for the C−Se bond and 272 kJ/mol for the C−S bond) and the bond lengths longer (C−Se 198 pm, C−S 181 pm and C−O 141 pm). Selenium compounds are more nucleophilic than the corresponding sulfur compounds and also more acidic. The p''K''a values of XH2 are 16 for oxygen, 7 for sulfur and 3.8 for selenium. In contrast to sulfoxides, the corresponding sel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Selenoxide
Organoselenium compounds (or seleno-organic) are chemical compounds containing carbon-to-selenium chemical bonds. Organoselenium chemistry is the corresponding science exploring their properties and reactivity. Selenium belongs with oxygen and sulfur to the group 16 elements or chalcogens, and similarities in chemistry are to be expected. Organoselenium compounds are found at trace levels in ambient waters, soils and sediments. Selenium can exist with oxidation state −2, +2, +4, +6. Se(II) is the dominant form in organoselenium chemistry. Down the group 16 column, the bond strength becomes increasingly weaker (234 kJ/ mol for the C−Se bond and 272 kJ/mol for the C−S bond) and the bond lengths longer (C−Se 198 pm, C−S 181 pm and C−O 141 pm). Selenium compounds are more nucleophilic than the corresponding sulfur compounds and also more acidic. The p''K''a values of XH2 are 16 for oxygen, 7 for sulfur and 3.8 for selenium. In contrast to sulfoxides, the corresponding se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diphenyl Ditelluride
Diphenylditelluride is the chemical compound with the formula (C6H5Te)2, abbreviated Ph2Te2 This orange-coloured solid is the oxidized derivative of the unstable benzenetellurol, PhTeH. Ph2Te2 is used as a source of the PhTe unit in organic synthesis and as a catalyst for redox reactions. Preparation Ph2Te2 is prepared by the oxidation of tellurophenolate, which is generated via the Grignard reagent:Crich, D.; Yao, Q. "Diphenyl Ditelluride" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. {{doi, 10.1002/047084289X.rd416. : PhMgBr + Te → PhTeMgBr :2PhTeMgBr + 0.5 O2 + H2O → Ph2Te2 + 2 MgBr(OH) The molecule has ''C2'' symmetry Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definit .... References Phenyl compounds O ... [...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] |
Stille Reaction
The Stille reaction is a chemical reaction widely used in organic synthesis. The reaction involves the coupling of two organic groups, one of which is carried as an organotin compound (also known as organostannanes). A variety of organic electrophiles provide the other coupling partner. The Stille reaction is one of many palladium-catalyzed coupling reactions.Hartwig, J. F. ''Organotransition Metal Chemistry, from Bonding to Catalysis''; University Science Books: New York, 2010. Stille, J. K. '' Angew. Chem. Int. Ed. Engl.'' 1986, ''25'', 508–524.ReviewFarina, V.; Krishnamurthy, V.; Scott, W. J. ''Org. React.'' 1998, ''50'', 1–652.Review : + \ \ce \ \overbrace^ + \!-\! :*\!,\ : Allyl, alkenyl, aryl, benzyl,acyl :*: halides (Cl, Br, I), pseudohalides (, OPO(OR)2), OAc The R1 group attached to the trialkyltin is normally sp2-hybridized, including vinyl, and aryl groups. These organostannanes are also stable to both air and moisture, and many of these reagents either are c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, and Biological Chemistry'. 1232 pages. Two general types of monoalkenes are distinguished: terminal and internal. Also called α-olefins, terminal alkenes are more useful. However, the International Union of Pure and Applied Chemistry (IUPAC) recommends using the name "alkene" only for acyclic hydrocarbons with just one double bond; alkadiene, alkatriene, etc., or polyene for acyclic hydrocarbons with two or more double bonds; cycloalkene, cycloalkadiene, etc. for cyclic ones; and "olefin" for the general class – cyclic or acyclic, with one or more double bonds. Acyclic alkenes, with only one double bond and no other functional groups (also known as mono-enes) form a homologous series of hydrocarbons with the general formula with '' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Selenoxide Elimination
Selenoxide elimination (also called α-selenation) is a method for the chemical synthesis of alkenes from selenoxides. It is most commonly used to synthesize α,β-unsaturated carbonyl compounds from the corresponding saturated analogues. It is mechanistically related to the Cope reaction. Mechanism and stereochemistry After the development of sulfoxide elimination as an effective method for generating carbon–carbon double bonds, it was discovered that selenoxides undergo a similar process, albeit much more rapidly. Most selenoxides decompose to the corresponding alkenes at temperatures between −50 and 40 °C. Evidence suggests that the elimination is ''syn''; however, epimerization at both carbon and selenium (both of which are stereogenic) may occur during the reaction. As selenoxides can be readily prepared from nucleophilic carbonyl derivatives (enols and enolates), selenoxide elimination has grown into a general method for the preparation of α,β-unsaturated carbo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sigmatropic Rearrangement
A sigmatropic reaction in organic chemistry is a pericyclic reaction wherein the net result is one σ-bond is changed to another σ-bond in an uncatalyzed intramolecular reaction. The name ''sigmatropic'' is the result of a compounding of the long-established sigma designation from single carbon–carbon bonds and the Greek word ''tropos'', meaning turn. In this type of rearrangement reaction, a substituent moves from one part of a π-bonded system to another part in an intramolecular reaction with simultaneous rearrangement of the π system. True sigmatropic reactions are usually uncatalyzed, although Lewis acid catalysis is possible. Sigmatropic reactions often have transition-metal catalysts that form intermediates in analogous reactions. The most well-known of the sigmatropic rearrangements are the ,3Cope rearrangement, Claisen rearrangement, Carroll rearrangement, and the Fischer indole synthesis. Overview of sigmatropic shifts Woodward–Hoffman sigmatropic shift nomencla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
