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Encyclopedia > Organoselenium compounds

Organoselenium chemistry is the corresponding science exploring the properties and reactivity of organoselenium compoundschemical compounds containing carbon to selenium bonds.[1][2][3] Selenium belongs with oxygen and sulfur to the group 16 elements and similarities in chemistry are to be expected. A chemical compound is a chemical substance formed from two or more elements, with a fixed ratio determining the composition. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... SE redirects here. ... A chemical bond is the physical phenomenon of chemical substances being held together by attraction of atoms to each other through sharing, as well as exchanging, of electrons or electrostatic forces. ... The chalcogens are the name for the periodic table group 16 (old-style: VIB or VIA) in the periodic table. ...


Selenium can exist with oxidation state +2 to -6. Down the column the bond strength becomes increasingly weaker (234 KJ/mole for the C-Se bond and 272 KJ/mole for the C-S bond) and the bond lengths longer (C-Se 198pm, C-S 181 pm and C-0 141 pm). Selenium compounds are more nucleophilic than the corresponding sulfur compounds and also more acidic. The pKa values of XH2 are 16 for oxygen, 7 for sulfur and 3.8 for selenium. In contrast to sulfoxides the corresponding selenoxides are unstable in the presence of β-protons and this property is utilized in many organic reactions of selenium, notably in selenoxide oxidations and in selenoxide eliminations. In chemistry, the oxidation state is a measure of the degree of oxidation of an atom in a chemical compound. ... In chemistry, bond strength is measured between two atoms joined in a chemical bond. ... KJ KJ (Born August 3 in Chicago, Illinois) is a singer and actor. ... Mole may mean: Mole (animal), a small burrowing mammal Mole (espionage), a spy working under deep cover Mole (sauce), a Mexican sauce made from chile peppers and other spices, including chocolate Mole (skin marking), a small spot of darkened pigment on the skin Mole (unit) is the SI unit for... Bond length or bond distance in molecular geometry is the distance between two bonded atoms in a molecule. ... In chemistry, a nucleophile (literally nucleus lover) is a reagent which is attracted to centres of positive charge. ... In chemistry and biochemistry, acid dissociation constant, the acidity constant, or the acid-ionization constant () is a specific type of equilibrium constant that indicates the extent of dissociation of hydrogen ions from an acid. ... A sulfoxide is a chemical compound containing a sulfinyl functional group with a sulfur oxygen double bond attached to two carbon atoms. ... Organic reactions are chemical reactions between organic compounds. ...

Contents


Selenium compounds

Selenols R-Se-H are the selenium equivalents of alcohols and thiols. These compounds are toxic and generally have an unpleasant smell. Phenylselenol or selenophenol is more acidic (pKa 5.9) than thiophenol (pKa 6.5) and also oxidizes more readily to the diselene. One synthetic procedure for selenophenol starts from phenylmagnesium bromide and elemental selenium with aqueous acidic workup. In chemistry, an alcohol is any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom of an alkyl or substituted alkyl group. ... In organic chemistry, a thiol is a compound that contains the functional group composed of a sulfur atom and a hydrogen atom (-SH). ... A Grignard Reagent is an alkyl- or aryl- magnesium halide. ...


Diselenes R-Se-Se-R are the selenium equivalents of peroxides and disulfides and used in organic chemistry as starting compounds for selenols and selenenyl halides R-Se-Cl or R-Se-Br. To meet Wikipedias quality standards, this article or section may require cleanup. ... In chemistry, a disulfide is an ion formed by sulfur atoms. ...


Selenides R-Se-R are the selenium equivalents of ethers and thioethers and the organic counterparts of inorganic Selenides. These compounds are ambiphilic on account of the identical electronegativities of carbon and selenium and can react as a nucleophile or an electrophile. They react as nucleophiles with alkyl halides R'-X to trivalent selenonium salts R'RRSe+X- but as electrophiles with organolithium reagents R'Li to the ate complex R'RRSe-Li+ in which the lone pair carbanion is stabilized by the unfilled selenium 4d orbital. This ate complex collapses back to a selenide but with exchange of ligands as in R'-se-Se. Ether is the general name for a class of chemical compounds which contain an ether group — an oxygen atom connected to two (substituted) alkyl groups. ... A thioether (also known as a sulfide) is a functional group in organic chemistry that has the structure R-S-R, where R is any organic group. ... The selenide ion is Se2-. A selenide is a chemical compound in which selenium serves as a anion with oxidation number of -2, much as sulfur does in a sulfide. ... Electronegativity is a measure of the ability of an atom or molecule to attract electrons in the context of a chemical bond. ... In chemistry, a nucleophile (literally nucleus lover) is a reagent which is attracted to centres of positive charge. ... In chemistry, an electrophile (literally electron-lover) is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile. ... In chemistry, an alkyl halide is an organic molecule of the form R_X, where X is a halide and R contains a carbon atom bonded to other functional groups or hydrogens. ... An organolithium reagent is an organometallic compound with a direct bond between a carbon and a lithium atom. ... A lone pair is an electron pair without bonding or sharing with other atoms. ... A carbanion is an anion in which carbon has an unshared pair of electrons and bears a negative charge usually with three substituents for a total of eight valence electrons. ...


Selenoxides R-Se=O-R are the selenium equivalents of sulfoxides which can be further oxidized to selenones R-SO2-R, sulfones with sulfur replaced again by selenium. A sulfoxide is a chemical compound containing a sulfinyl functional group with a sulfur oxygen double bond attached to two carbon atoms. ... A sulfone is a chemical compound containing a sulfonyl functional group attached to two carbon atoms. ...


Selenoxide oxidations

Allylic oxidation is an organic oxidation converting an allylic methylene group into an allylic alcohol or an ketone. This chemical transformation is an important organic reaction. Selenium dioxide is one representative of a group of oxidizing agents that can bring about this reaction. Organic reductions or organic oxidations or organic redox reactions are redox reactions that take place with organic compounds. ... An allyl group is an alkene hydrocarbon group with the formula H2C=CH-CH2-. It is made up of a vinyl group, CH2=CH-, attached to a methylene -CH2. ... In chemistry, methylene is a divalent functional group CH2 derived formally from methane. ... Allyl alcohol or 2-propen-1-ol is an organic compound. ... Ketone group A ketone is either the functional group characterized by a carbonyl group linked to two other carbon atoms or a chemical compound that contains this functional group. ... Organic reactions are chemical reactions between organic compounds. ... R-phrases , , S-phrases , , , , U.S. Permissible Exposure Limit 5 ppm IDLH (NIOSH) 100 ppm Flash point non-flammable RTECS number WS4550000 Supplementary data page Structure and properties n, εr, etc. ... European Union Chemical hazard symbol for oxidizing agents Dangerous goods label for oxidising agents An oxidizing agent is a compound that oxidizes another substance in electrochemistry or redox chemical reactions. ...

This type of reaction often involves free radicals but in some cases a pericyclic concerted reaction mechanism is found for selenium oxide oxidations. The first step is an ene reaction, transferring the allylic proton to the selenium oxide, and the second step is a [2,3] sigmatropic reaction. Image File history File links SeleniumdioxideOxidation. ... For other uses, see radical. ... In organic chemistry, a pericyclic reaction is a type of reaction where the transition state of molecule has a cyclic geometry, and the reaction progresses in a concerted reactions fashion. ... In chemistry, a concerted reaction is one that takes place in a single step. ... In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs. ... Ene reactions are Group transfer reactions between an alkyne or alkene, or similar double bonded species and an allyl-like species. ... A Sigmatropic reaction is a pericyclic reaction where the net result is one sigma bond being changed to another sigma bond. ...


Oxidations involving selenium dioxide are often carried out with catalytic amounts of the selenium compound and in presence of a sacrificial catalyst or co-oxidant such as hydrogen peroxide or disodium hydrogen phosphate. Selenious acid (H2SeO3) and pyridinium chlorochromate are other oxidizing reagents. A catalytic cycle in chemistry is a concept that appreciates the notion that in a chemical reaction a catalyst is often first consumed and then regenerated in the course of a catalytic reaction sequence thereby elaborating on the classical view that of a catalyst not taking part in the reaction... Hydrogen peroxide (H2O2) is a very pale blue liquid which appears clear in a dilute solution, slightly more viscous than water. ... Pyridinium chlorochromate, a reddish orange solid reagent, is used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones. ...


The type of substrate can be extended to α-carbonyl compounds such as ketones converting them to diketones Ketone group A ketone is either the functional group characterized by a carbonyl group linked to two other carbon atoms or a chemical compound that contains this functional group. ...


Selenoxide eliminations

In presence of a β-proton, a selenide will give an elimination reaction after oxidation to an alkene and leaving a selenol. In the elimination reaction all five participating reaction centers a coplanar and therefore the reaction mode is syn. oxidizing agents are hydrogen peroxide, ozone or MCPBA. This reaction type is often used with ketones leading to enones. An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a one or two-step mechanism. ... An alkene in organic chemistry is an unsaturated hydrocarbon containing at least one carbon to carbon double bond. ... A set of points is said to be coplanar if and only if they lie on the same geometric plane. ... Hydrogen peroxide (H2O2) is a very pale blue liquid which appears clear in a dilute solution, slightly more viscous than water. ... For other uses, see Ozone (disambiguation). ... A peroxy acid, is an acid in which an acidic -OH group has been replaced by an -OOH group. ... Ketone group A ketone is either the functional group characterized by a carbonyl group linked to two other carbon atoms or a chemical compound that contains this functional group. ... An enone is an unsaturated chemical compound or functional group consisting of a conjugated system of an alkene and a ketone. ...

Scheme 2. Selenoxide elimination of carbonyl compounds

The Grieco elimination is a similar selenoxide elimination with o-nitrophenylselenocyanate and tributylphosphine. The Grieco elimination is an organic reaction describing the elimination reaction of an aliphatic primary alcohol through a selenide to a terminal alkene . ...


See also

The chalcogens are the name for the periodic table group 16 (old-style: VIB or VIA) in the periodic table. ... This page is a candidate for speedy deletion, because: no useful content If you disagree with its speedy deletion, please explain why on its talk page or at Wikipedia:Speedy deletions. ...

External links

Cycloheptatriene Cycloheptatriene (CHT), or 1,3,5-cycloheptatriene, is a clear, yellow to brown, flammable liquid with melting point -80 °C and boiling point 116 °C, insoluble in water. ... A huge KDP crystal grown at LLNL to be cut into slices and used on the National Ignition Facility. ... Organic Syntheses is a scientific journal that Since 1921 has provided the chemistry community with annual collections of detailed and checked procedures for the organic synthesis of organic compounds. ... The chemical compound pinene is a bicyclic terpene known as a monoterpene. ... Organic Syntheses is a scientific journal that Since 1921 has provided the chemistry community with annual collections of detailed and checked procedures for the organic synthesis of organic compounds. ... Cyclohexanone is six-carbon cyclic molecule with a ketone functional group. ... Organic Syntheses is a scientific journal that Since 1921 has provided the chemistry community with annual collections of detailed and checked procedures for the organic synthesis of organic compounds. ... Paraldehyde is the cyclic form of three acetaldehyde molecules (a trimer). ... Glyoxal is an organic compound. ... Organic Syntheses is a scientific journal that Since 1921 has provided the chemistry community with annual collections of detailed and checked procedures for the organic synthesis of organic compounds. ... Sodium hydride is a highly flammable, and corrosive chemical compound with formula NaH and CAS number 7646-69-7. ... Organic Syntheses is a scientific journal that Since 1921 has provided the chemistry community with annual collections of detailed and checked procedures for the organic synthesis of organic compounds. ... A Grignard Reagent is an alkyl- or aryl- magnesium halide. ... Organic Syntheses is a scientific journal that Since 1921 has provided the chemistry community with annual collections of detailed and checked procedures for the organic synthesis of organic compounds. ... Bromobenzene are a group of halogenobenzenes formed in a substitution reaction between bromine and benzene with a hydrogen benzene biproduct. ... Organic Syntheses is a scientific journal that Since 1921 has provided the chemistry community with annual collections of detailed and checked procedures for the organic synthesis of organic compounds. ...

References

  1.   A. Krief, L. Hevesi, Organoselenium Chemistry I. Functional Group Transformations., Springer, Berlin, 1988 ISBN 0-387-18629-8
  2.   S. Patai, Z. Rappoport (Eds.), The Chemistry of Organic Selenium and Tellurium Compounds, John. Wiley and Sons, Chichester, Vol. 1, 1986 ISBN 0-471-90425-2
  3.   Paulmier, C. Selenium Reagents and Intermediates in Organic Synthesis; Baldwin, J. E., Ed.; Pergamon Books Ltd.: New York, 1986 ISBN 0-08-032484-3

 
 

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