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W. Clark Still
William Clark Still (born 1946) is an American organic chemistry, organic chemist. As a distinguished professor at Columbia University, Clark Still made significant contributions to the field of organic chemistry, particularly in the areas of natural product synthesis, reaction development, conformational analysis, macrocyclic stereocontrol, and computational chemistry. Still and coworkers also developed the purification technique known as flash column chromatography which is widely used for the purification of organic compounds. Major contributions Total synthesis Periplanone B In 1979, Still reported the first total synthesis of periplanone B, the potent sex pheromone of the American cockroach. Although the structural connectivity of this compound had been established spectroscopically, Still's synthesis confirmed the relative stereochemical relationships present in this natural product. A key step in this synthesis makes use of an anionic oxy-Cope rearrangement to form th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Augusta, Georgia
Augusta ( ), officially Augusta–Richmond County, is a consolidated city-county on the central eastern border of the U.S. state of Georgia. The city lies across the Savannah River from South Carolina at the head of its navigable portion. Georgia's third-largest city after Atlanta and Columbus, Augusta is located in the Fall Line section of the state. According to the U.S. Census Bureau, Augusta–Richmond County had a 2020 population of 202,081, not counting the unconsolidated cities of Blythe and Hephzibah. It is the 116th largest city in the United States. The process of consolidation between the City of Augusta and Richmond County began with a 1995 referendum in the two jurisdictions. The merger was completed on July 1, 1996. Augusta is the principal city of the Augusta metropolitan area. In 2020 it had a population of 611,000, making it the second-largest metro area in the state. It is the 95th largest metropolitan area in the United States. Augusta was established ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
18-crown-6
18-Crown-6 is an organic compound with the formula 2H4Osub>6 and the IUPAC name of 1,4,7,10,13,16-hexaoxacyclooctadecane. It is a white, hygroscopic crystalline solid with a low melting point. Like other crown ethers, 18-crown-6 functions as a ligand for some metal cations with a particular affinity for potassium cations (binding constant in methanol: 106 M−1). The point group of 18-crown-6 is S6. The dipole moment of 18-crown-6 varies in different solvent and under different temperature. Under 25 °C, the dipole moment of 18-crown-6 is in cyclohexane and in benzene. The synthesis of the crown ethers led to the awarding of the Nobel Prize in Chemistry to Charles J. Pedersen. Synthesis This compound is prepared by a modified Williamson ether synthesis in the presence of a templating cation: It can be also prepared by the oligomerization of ethylene oxide: :(CH2OCH2CH2Cl)2 + (CH2OCH2CH2OH)2 + 2 KOH → (CH2CH2O)6 + 2 KCl + 2 H2O It can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organotin
Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents. Organotin chemistry is part of the wider field of organometallic chemistry. The first organotin compound was diethyltin diiodide (), discovered by Edward Frankland in 1849. The area grew rapidly in the 1900s, especially after the discovery of the Grignard reagents, which are useful for producing Sn–C bonds. The area remains rich with many applications in industry and continuing activity in the research laboratory. Structure Organotin compounds are generally classified according to their oxidation states. Tin(IV) compounds are much more common and more useful. Organic derivatives of tin(IV) The tetraorgano derivatives are invariably tetrahedral. Compounds of the type SnRR'R''R have been resolved into individual enantiomers. Organotin halides Organotin chlorides have the formula for values of ''n'' up to 3. Bromides, iodides, and fluorides are also known but less important. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
2,3-sigmatropic Rearrangement
2,3-Sigmatropic rearrangements are a type of sigmatropic rearrangements and can be classified into two types. Rearrangements of allylic sulfoxides, amine oxides, selenoxides are neutral. Rearrangements of carbanions of allyl ethers are anionic. The general scheme for this kind of rearrangement is: Atom Y may be sulfur, selenium, or nitrogen. If Y is nitrogen, the reaction is referred to as the Sommelet–Hauser rearrangement if a quaternary ammonium salt is involved or the aza-Wittig reaction if an alpha-metalated tertiary amine is involved; if Y is oxygen, then it is called a 2,3-Wittig rearrangement (not to be confused with the well-known Wittig reaction, which involves a phosphonium ylide). If Y is sulfur, the product can be treated with a thiophil to generate an allylic alcohol in what is known as the Mislow–Evans rearrangement. A ,3rearrangement may result in carbon-carbon bond formation. It can also be used as a ring-expansion reaction.''Ring expansion by 2, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
2,3-Wittig Rearrangement
The ,3Wittig rearrangement is the transformation of an allylic ether into a homoallylic alcohol via a concerted, pericyclic process. Because the reaction is concerted, it exhibits a high degree of stereocontrol, and can be employed early in a synthetic route to establish stereochemistry. The Wittig rearrangement requires strongly basic conditions, however, as a carbanion intermediate is essential. ,2Wittig rearrangement is a competitive process. Introduction ,3Sigmatropic rearrangements occur for a variety of groups X and Y (see below). When X is a carbanion and Y an alkoxide, the rearrangement is called the ,3Wittig rearrangement and the products are pent-1-en-5-ols. The ,2Wittig rearrangement, which produces isomeric pent-5-en-1-ols, is a competitive process that takes place at high temperatures. Because of the high atom economy and stereoselectivity of the ,3rearrangement, it has gained considerable synthetic utility. The carbanion is generated by direct lithiation of m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Para-toluenesulfonic Acid
''p''-Toluenesulfonic acid (PTSA or ''p''TsOH) or tosylic acid (TsOH) is an organic compound with the formula CH3 C6H4 SO3H. It is a white extremely hygroscopic solid that is soluble in water, alcohols, and other polar organic solvents. The CH3C6H4SO2 group is known as the tosyl group and is often abbreviated as Ts or Tos. Most often, TsOH refers to the monohydrate, TsOH.H2O. As with other aryl sulfonic acids, TsOH is a strong organic acid. It is about one million times stronger than benzoic acid. It is one of the few strong acids that is solid and therefore is conveniently weighed and stored. Preparation and uses TsOH is prepared on an industrial scale by the sulfonation of toluene. Common impurities include benzenesulfonic acid and sulfuric acid. TsOH monohydrate contains an amount of water. To estimate the total moisture present as impurity, the Karl Fischer method is used. Impurities can be removed by recrystallization from its concentrated aqueous solution followed by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Still Monensin
A still is an apparatus used to distill liquid mixtures by heating to selectively boil and then cooling to condense the vapor. A still uses the same concepts as a basic distillation apparatus, but on a much larger scale. Stills have been used to produce perfume and medicine, water for injection (WFI) for pharmaceutical use, generally to separate and purify different chemicals, and to produce distilled beverages containing ethanol. Application Since ethanol boils at a much lower temperature than water, simple distillation can separate ethanol from water by applying heat to the mixture. Historically, a copper vessel was used for this purpose, since copper removes undesirable sulfur-based compounds from the alcohol. However, many modern stills are made of stainless steel pipes with copper linings to prevent erosion of the entire vessel and lower copper levels in the waste product (which in large distilleries is processed to become animal feed). Copper is the preferred material ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cram-Felkin-Anh
In stereochemistry, asymmetric induction (also enantioinduction) describes the preferential formation in a chemical reaction of one enantiomer or diastereoisomer over the other as a result of the influence of a chiral feature present in the substrate, reagent, catalyst or environment. Asymmetric induction is a key element in asymmetric synthesis. Asymmetric induction was introduced by Hermann Emil Fischer based on his work on carbohydrates. Several types of induction exist. Internal asymmetric induction makes use of a chiral center bound to the reactive center through a covalent bond and remains so during the reaction. The starting material is often derived from chiral pool synthesis. In relayed asymmetric induction the chiral information is introduced in a separate step and removed again in a separate chemical reaction. Special synthons are called chiral auxiliaries. In external asymmetric induction chiral information is introduced in the transition state through a catalyst of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lithium Diisopropylamide
Lithium diisopropylamide (commonly abbreviated LDA) is a chemical compound with the molecular formula . It is used as a strong base and has been widely utilized due to its good solubility in non-polar organic solvents and non-nucleophilic nature. It is a colorless solid, but is usually generated and observed only in solution. It was first prepared by Hamell and Levine in 1950 along with several other hindered lithium diorganylamides to effect the deprotonation of esters at the α position without attack of the carbonyl group. Preparation and structure LDA is commonly formed by treating a cooled (0 to −78 °C) mixture of tetrahydrofuran and diisopropylamine with ''n''-butyllithium. When dissociated, the diisopropylamide anion can become protonated to form diisopropylamine. Diisopropylamine has a p''K''a value of 36. Therefore, its conjugate base is suitable for the deprotonation of compounds with greater acidity, importantly, such weakly acidic compounds (carbon acids) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aldol Reaction
The aldol reaction is a means of forming carbon–carbon bonds in organic chemistry. Discovered independently by the Russian chemist Alexander Borodin in 1869 and by the French chemist Charles-Adolphe Wurtz in 1872, the reaction combines two carbonyl compounds (the original experiments used aldehydes) to form a new β-hydroxy carbonyl compound. These products are known as '' aldols'', from the ''ald''ehyde + alcoh''ol'', a structural motif seen in many of the products. Aldol structural units are found in many important molecules, whether naturally occurring or synthetic. For example, the aldol reaction has been used in the large-scale production of the commodity chemical pentaerythritol and the synthesis of the heart disease drug Lipitor ( atorvastatin, calcium salt). The aldol reaction unites two relatively simple molecules into a more complex one. Increased complexity arises because up to two new stereogenic centers (on the α- and β-carbon of the aldol adduct, marked w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monensin
Monensin is a polyether antibiotic isolated from ''Streptomyces cinnamonensis''. It is widely used in ruminant animal feeds. The structure of monensin was first described by Agtarap et al. in 1967, and was the first polyether antibiotic to have its structure elucidated in this way. The first total synthesis of monensin was reported in 1979 by Yoshito Kishi, Kishi et al. Mechanism of action Monensin A is an ionophore related to the crown ethers with a preference to form complexes with monovalent cations such as: Li+, Na+, K+, Rb+, Ag+, and Tl+. Monensin A is able to transport these cations across lipid membranes of cells in an electroneutral (i.e. non-depolarizing) exchange, playing an important role as an Na+/H+ antiporter. Recent studies have shown that monensin may transport sodium ion through the membrane in both electrogenic and electroneutral manner. This approach explains ionophoric ability and in consequence antibacterial properties of not only parental monensin, but also ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sarett Oxidation
The Sarett oxidation is an organic reaction that oxidizes primary and secondary alcohols to aldehydes and ketones, respectively, using chromium trioxide and pyridine. Unlike the similar Jones oxidation, the Sarett oxidation will not further oxidize primary alcohols to their carboxylic acid form, neither will it affect carbon-carbon double bonds. Use of the original Sarett oxidation has become largely antiquated however, in favor of other modified oxidation techniques. The unadulterated reaction is still occasionally used in teaching settings and in small scale laboratory research. History First appearance The reaction is named after the American chemist Lewis Hastings Sarett (1917–1999). The first description of its use appears in a 1953 article co-authored by Sarett that relates to the synthesis of adrenal steroids. The paper proposes the use of the pyridine chromium complex CrO3-2C5H5N to oxidize primary and secondary alcohols. The complex would later become known as the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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