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Weinreb Amide
The Weinreb–Nahm ketone synthesis is a chemical reaction used in organic chemistry to make carbon–carbon bonds. It was discovered in 1981 by Steven M. Weinreb and Steven Nahm as a method to synthesize ketones. The original reaction involved two subsequent nucleophilic acyl substitutions: the conversion of an acid chloride with N,O-Dimethylhydroxylamine, to form a Weinreb–Nahm amide, and subsequent treatment of this species with an organometallic reagent such as a Grignard reagent or organolithium reagent. Nahm and Weinreb also reported the synthesis of aldehydes by reduction of the amide with an excess of lithium aluminum hydride (see amide reduction). The major advantage of this method over addition of organometallic reagents to more typical acyl compounds is that it avoids the common problem of over-addition. For these latter reactions, two equivalents of the incoming group add to form an alcohol rather than a ketone or aldehyde. This occurs even if the equivalents o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Steven M
Stephen or Steven is a common English first name. It is particularly significant to Christians, as it belonged to Saint Stephen ( grc-gre, Στέφανος ), an early disciple and deacon who, according to the Book of Acts, was stoned to death; he is widely regarded as the first martyr (or "protomartyr") of the Christian Church. In English, Stephen is most commonly pronounced as ' (). The name, in both the forms Stephen and Steven, is often shortened to Steve or Stevie. The spelling as Stephen can also be pronounced which is from the Greek original version, Stephanos. In English, the female version of the name is Stephanie. Many surnames are derived from the first name, including Stephens, Stevens, Stephenson, and Stevenson, all of which mean "Stephen's (son)". In modern times the name has sometimes been given with intentionally non-standard spelling, such as Stevan or Stevon. A common variant of the name used in English is Stephan ; related names that have found some curr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equivalent (chemistry)
An equivalent (symbol: officially equiv; unofficially but often Eq) is the amount of a substance that reacts with (or is ''equivalent'' to) an arbitrary amount (typically one mole) of another substance in a given chemical reaction. It is an archaic unit of measurement that was used in chemistry and the biological sciences (see '). The mass of an equivalent is called its equivalent weight. Formula : ''milligrams to = mg x V / MW'' :: Example for elemental compounds: (mg element / elemental compound mass fraction) x V / MV : '' to milligrams = mEq x MW / V'' Common examples mEq to milligram Milligram to mEq Formal definition In a more formal definition, the ''equivalent'' is the amount of a substance needed to do one of the following: * react with or supply one mole of hydrogen ions () in an acid–base reaction * react with or supply one mole of electrons in a redox reaction. The "hydrogen ion" and the "electron" in these examples are respectively called the "reaction ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Work-up (chemistry)
In chemistry, work-up refers to the series of manipulations required to isolate and purify the product(s) of a chemical reaction. Typically, these manipulations may include: * quenching a reaction to deactivate any unreacted reagents. * cooling the reaction mixture or adding an ''antisolvent'' to induce precipitation, and collecting or removing the solids by filtration, decantation, or centrifugation * removal of solvents by evaporation * separating the reaction mixture into organic and aqueous layers by liquid-liquid extraction * purification by chromatography, distillation or recrystallization For example, the Grignard reaction between phenylmagnesium bromide and carbon dioxide in the form of dry ice gives the conjugate base of benzoic acid. The desired product, benzoic acid, is obtained by the following work-up:{{cite book , title = Introduction to Organic Laboratory Techniques: A Small Scale Approach , author = Donald L. Pavia , year = 2004 , publisher = Thomson Brooks ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Methoxy
In organic chemistry, a methoxy group is the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula . On a benzene ring, the Hammett equation classifies a methoxy substituent at the ''para'' position as an electron-donating group, but as an electron-withdrawing group if at the ''meta'' position. At the ''ortho'' position, steric effects are likely to cause a significant alteration in the Hammett equation prediction which otherwise follows the same trend as that of the ''para'' position. Occurrence The simplest of methoxy compounds are methanol and dimethyl ether. Other methoxy ethers include anisole and vanillin. Many alkoxides contain methoxy groups, e.g. tetramethyl orthosilicate and titanium methoxide. Such compounds are often classified as methoxides. Esters with a methoxy group can be referred to as methyl esters, and the —COOCH3 substituent is called a methoxycarbonyl. Biosynthesis In nature, methoxy groups are found on nucleosi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chelation
Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a Denticity, polydentate (multiple bonded) ligand and a single central metal atom. These ligands are called chelants, chelators, chelating agents, or sequestering agents. They are usually organic compounds, but this is not a necessity, as in the case of zinc and its use as a maintenance therapy to prevent the absorption of copper in people with Wilson's disease. Chelation is useful in applications such as providing nutritional supplements, in chelation therapy to remove toxic metals from the body, as contrast medium, contrast agents in MRI, MRI scanning, in manufacturing using homogeneous catalysts, in chemical water treatment to assist in the removal of metals, and in fertilizers. Chelate effect The chelate effect is the greater affinity of chelating ligands for a metal ion than that of similar nonchelating (monodentate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleophilic Addition
In organic chemistry, a nucleophilic addition reaction is an addition reaction where a chemical compound with an electrophilic double or triple bond reacts with a nucleophile, such that the double or triple bond is broken. Nucleophilic additions differ from electrophilic additions in that the former reactions involve the group to which atoms are added accepting electron pairs, whereas the latter reactions involve the group donating electron pairs. Addition to carbon–heteroatom double bonds Nucleophilic addition reactions of nucleophiles with electrophilic double or triple bond (π bonds) create a new carbon center with two additional single, or σ, bonds.March Jerry; (1985). Advanced Organic Chemistry reactions, mechanisms and structure (3rd ed.). New York: John Wiley & Sons, inc. Addition of a nucleophile to carbon–heteroatom double or triple bonds such as >C=O or -C≡N show great variety. These types of bonds are polar (have a large difference in electronegativity betwe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetrahedral Intermediate
A tetrahedral intermediate is a reaction intermediate in which the bond arrangement around an initially double-bonded carbon atom has been transformed from trigonal to tetrahedral. Tetrahedral intermediates result from nucleophilic addition to a carbonyl group. The stability of tetrahedral intermediate depends on the ability of the groups attached to the new tetrahedral carbon atom to leave with the negative charge. Tetrahedral intermediates are very significant in organic syntheses and biological systems as a key intermediate in esterification, transesterification, ester hydrolysis, formation and hydrolysis of amides and peptides, hydride reductions, and other chemical reactions. History One of the earliest accounts of the tetrahedral intermediate came from Rainer Ludwig Claisen in 1887. In the reaction of benzyl benzoate with sodium methoxide, and methyl benzoate with sodium benzyloxide, he observed a white precipitate which under acidic conditions yields benzyl benzoate, methyl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reaction Mechanism
In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs. A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of an overall chemical reaction. The detailed steps of a reaction are not observable in most cases. The conjectured mechanism is chosen because it is thermodynamically feasible, and has experimental support in isolated intermediates (see next section) or other quantitative and qualitative characteristics of the reaction. It also describes each reactive intermediate, activated complex, and transition state, and which bonds are broken (and in what order), and which bonds are formed (and in what order). A complete mechanism must also explain the reason for the reactants and catalyst used, the stereochemistry observed in reactants and products, all products formed and the amount of each. The electron or arrow pushing method is often used in i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weinreb Ketone Synthesis
The Weinreb–Nahm ketone synthesis is a chemical reaction used in organic chemistry to make carbon–carbon bonds. It was discovered in 1981 by Steven M. Weinreb and Steven Nahm as a method to synthesize ketones. The original reaction involved two subsequent nucleophilic acyl substitutions: the conversion of an acid chloride with N,O-Dimethylhydroxylamine, to form a Weinreb–Nahm amide, and subsequent treatment of this species with an organometallic reagent such as a Grignard reagent or organolithium reagent. Nahm and Weinreb also reported the synthesis of aldehydes by reduction of the amide with an excess of lithium aluminum hydride (see amide reduction). The major advantage of this method over addition of organometallic reagents to more typical acyl compounds is that it avoids the common problem of over-addition. For these latter reactions, two equivalents of the incoming group add to form an alcohol rather than a ketone or aldehyde. This occurs even if the equivalents o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organic Letters
''Organic Letters'' is a biweekly peer-reviewed scientific journal covering research in organic chemistry. It was established in 1999 and is published by the American Chemical Society. In 2014, the journal moved to a hybrid open access publishing model. The founding editor-in-chief was Amos Smith. Since 2019, Erick M. Carreira serves as the editor-in-chief. The journal is abstracted and indexed in: the Science Citation Index Expanded, Scopus, Academic Search Premier, BIOSIS Previews, Chemical Abstracts Service, EMBASE, and MEDLINE MEDLINE (Medical Literature Analysis and Retrieval System Online, or MEDLARS Online) is a bibliographic database of life sciences and biomedical information. It includes bibliographic information for articles from academic journals covering medic .... References External links * American Chemical Society academic journals Biweekly journals Organic chemistry journals Publications established in 1999 English-language journals {{chem-journ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Natural Product
A natural product is a natural compound or substance produced by a living organism—that is, found in nature. In the broadest sense, natural products include any substance produced by life. Natural products can also be prepared by chemical synthesis (both semisynthesis and total synthesis) and have played a central role in the development of the field of organic chemistry by providing challenging synthetic targets. The term natural product has also been extended for commercial purposes to refer to cosmetics, dietary supplements, and foods produced from natural sources without added artificial ingredients. Within the field of organic chemistry, the definition of natural products is usually restricted to organic compounds isolated from natural sources that are produced by the pathways of primary or secondary metabolism. Within the field of medicinal chemistry, the definition is often further restricted to secondary metabolites. Secondary metabolites (or specialized metabolites ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
