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Tert-Butyldiphenylsilyl
''tert''-Butyldiphenylsilyl, also known as TBDPS, is a protecting group for alcohols. Its formula is C16H19Si-. Development The ''tert''-butyldiphenylsilyl group was first suggested as a protecting group by Hanessian and Lavallée in 1975. It was designed to supersede the use of Corey's ''tert''-butyldimethylsilyl as a protecting group for alcohols: The novel features that they highlight are the increased resistance to acidic hydrolysis and increased selectivity towards protection of primary hydroxyl groups. The group is unaffected by treatment with 80% acetic acid, which catalyses the deprotection of O-tetrapyranyl, O-trityl and O-tert-butyldimethylsilyl ethers. It is also unaffected by 50% trifluoroacetic acid (TFA), and survives the harsh acidic conditions used to install and remove isopropylidene or benzylidene acetals. Applications in chemical synthesis The TBDPS group is prized for its increased stability towards acidic conditions and nucleophilic species over the othe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TBDPS Tert-Butyldiphenylsilyl
''tert''-Butyldiphenylsilyl, also known as TBDPS, is a protecting group for alcohols. Its formula is C16H19Si-. Development The ''tert''-butyldiphenylsilyl group was first suggested as a protecting group by Hanessian and Lavallée in 1975. It was designed to supersede the use of Corey's ''tert''-butyldimethylsilyl as a protecting group for alcohols: The novel features that they highlight are the increased resistance to acidic hydrolysis and increased selectivity towards protection of primary hydroxyl groups. The group is unaffected by treatment with 80% acetic acid, which catalyses the deprotection of O-tetrapyranyl, O-trityl and O-tert-butyldimethylsilyl ethers. It is also unaffected by 50% trifluoroacetic acid (TFA), and survives the harsh acidic conditions used to install and remove isopropylidene or benzylidene acetals. Applications in chemical synthesis The TBDPS group is prized for its increased stability towards acidic conditions and nucleophilic species over the othe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silyl Ether
Silyl ethers are a group of chemical compounds which contain a silicon atom covalently bonded to an alkoxy group. The general structure is R1R2R3Si−O−R4 where R4 is an alkyl group or an aryl group. Silyl ethers are usually used as protecting groups for alcohols in organic synthesis. Since R1R2R3 can be combinations of differing groups which can be varied in order to provide a number of silyl ethers, this group of chemical compounds provides a wide spectrum of selectivity for protecting group chemistry. Common silyl ethers are: trimethylsilyl (TMS), ''tert''-butyldiphenylsilyl (TBDPS), ''tert''-butyldimethylsilyl (TBS/TBDMS) and triisopropylsilyl (TIPS). They are particularly useful because they can be installed and removed very selectively under mild conditions. Common silyl ethers Formation Commonly silylation of alcohols requires a silyl chloride and an amine base. One reliable and rapid procedure is the Corey protocol in which the alcohol is reacted with a silyl chlori ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triisopropylsilyl
Silyl ethers are a group of chemical compounds which contain a silicon atom covalently bonded to an alkoxy group. The general structure is R1R2R3Si−O−R4 where R4 is an alkyl group or an aryl group. Silyl ethers are usually used as protecting groups for alcohols in organic synthesis. Since R1R2R3 can be combinations of differing groups which can be varied in order to provide a number of silyl ethers, this group of chemical compounds provides a wide spectrum of selectivity for protecting group chemistry. Common silyl ethers are: trimethylsilyl (TMS), ''tert''-butyldiphenylsilyl (TBDPS), ''tert''-butyldimethylsilyl (TBS/TBDMS) and triisopropylsilyl (TIPS). They are particularly useful because they can be installed and removed very selectively under mild conditions. Common silyl ethers Formation Commonly silylation of alcohols requires a silyl chloride and an amine base. One reliable and rapid procedure is the Corey protocol in which the alcohol is reacted with a silyl chlori ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silver Nitrate
Silver nitrate is an inorganic compound with chemical formula . It is a versatile precursor to many other silver compounds, such as those used in photography. It is far less sensitive to light than the halides. It was once called ''lunar caustic'' because silver was called ''luna'' by ancient alchemists who associated silver with the moon. In solid silver nitrate, the silver ions are three- coordinated in a trigonal planar arrangement. Synthesis and structure Albertus Magnus, in the 13th century, documented the ability of nitric acid to separate gold and silver by dissolving the silver. Indeed silver nitrate can be prepared by dissolving silver in nitric acid followed by evaporation of the solution. The stoichiometry of the reaction depends upon the concentration of nitric acid used. :3 Ag + 4 HNO3 (cold and diluted) → 3 AgNO3 + 2 H2O + NO :Ag + 2 HNO3 (hot and concentrated) → AgNO3 + H2O + NO2 The structure of silver nitrate has been examined by X-ray crystallography sever ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radical (chemistry)
In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron. With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spontaneously dimerize. Most organic radicals have short lifetimes. A notable example of a radical is the hydroxyl radical (HO·), a molecule that has one unpaired electron on the oxygen atom. Two other examples are triplet oxygen and triplet carbene (꞉) which have two unpaired electrons. Radicals may be generated in a number of ways, but typical methods involve redox reactions. Ionizing radiation, heat, electrical discharges, and electrolysis are known to produce radicals. Radicals are intermediates in many chemical reactions, more so than is apparent from the balanced equations. Radicals are important in combustion, atmospheric chemistry, polymerization, plasma chemistry, biochemistry, and many other chemical processes. A majority of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrophile
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carries a partial positive charge, or have an atom that does not have an octet of electrons. Electrophiles mainly interact with nucleophiles through addition and substitution reactions. Frequently seen electrophiles in organic syntheses include cations such as H+ and NO+, polarized neutral molecules such as HCl, alkyl halides, acyl halides, and carbonyl compounds, polarizable neutral molecules such as Cl2 and Br2, oxidizing agents such as organic peracids, chemical species that do not satisfy the octet rule such as carbenes and radicals, and some Lewis acids such as BH3 and DIBAL. Organic chemistry Addition of halogens These occur between alkenes and electrophiles, often halogens as in halogen addition reactions. Common reactions i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleophile
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases. ''Nucleophilic'' describes the affinity of a nucleophile to bond with positively charged atomic nuclei. Nucleophilicity, sometimes referred to as nucleophile strength, refers to a substance's nucleophilic character and is often used to compare the affinity of atoms. Neutral nucleophilic reactions with solvents such as alcohols and water are named solvolysis. Nucleophiles may take part in nucleophilic substitution, whereby a nucleophile becomes attracted to a full or partial positive charge, and nucleophilic addition. Nucleophilicity is closely related to basicity. History The terms ''nucleophile'' and ''electrophile'' were introduced by Christopher Kelk Ingold in 1933, replacing the terms ''anionoid'' and ''cationoid' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxidising Agent
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxidizer is any substance that oxidizes another substance. The oxidation state, which describes the degree of loss of electrons, of the oxidizer decreases while that of the reductant increases; this is expressed by saying that oxidizers "undergo reduction" and "are reduced" while reducers "undergo oxidation" and "are oxidized". Common oxidizing agents are oxygen, hydrogen peroxide and the halogens. In one sense, an oxidizing agent is a chemical species that undergoes a chemical reaction in which it gains one or more electrons. In that sense, it is one component in an oxidation–reduction (redox) reaction. In the second sense, an oxidizing agent is a chemical species that transfers electronegative atoms, usually oxygen, to a substrate. Combus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reducing Agent
In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth metals, formic acid, oxalic acid, and sulfite compounds. In their pre-reaction states, reducers have extra electrons (that is, they are by themselves reduced) and oxidizers lack electrons (that is, they are by themselves oxidized). This is commonly expressed in terms of their oxidation states. An agent's oxidation state describes its degree of loss of electrons, where the higher the oxidation state then the fewer electrons it has. So initially, prior to the reaction, a reducing agent is typically in one of its lower possible oxidation states; its oxidation state increases during the reaction while that of the oxidizer decreases. Thus in a redox reaction, the agent whose oxidation state increases, that "loses/Electron donor, donates electrons ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hexamethylphosphoramide
Hexamethylphosphoramide, often abbreviated HMPA, is a phosphoramide (an amide of phosphoric acid) with the formula This colorless liquid is a useful reagent in organic synthesis. Structure and reactivity HMPA is the oxide of the highly basic tertiary phosphine hexamethylphosphorous triamide (HMPT), P(NMe2)3. Like other phosphine oxides (such as triphenylphosphine oxide), the molecule has a tetrahedral core and a P=O bond that is highly polarized, with significant negative charge residing on the oxygen atom. Compounds containing a nitrogen–phosphorus bond typically are degraded by hydrochloric acid to form a protonated amine and phosphate. It dissolves alkali metal salts and alkali metals, forming blue solutions which are stable for a few hours. Solvated electrons are present in these blue solutions. Applications HMPA is a specialty solvent for polymers, gases, and organometallic compounds. It improves the selectivity of lithiation reactions by breaking up the oligomers of lit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sodium Hydride
Sodium hydride is the chemical compound with the empirical formula Na H. This alkali metal hydride is primarily used as a strong yet combustible base in organic synthesis. NaH is a saline (salt-like) hydride, composed of Na+ and H− ions, in contrast to molecular hydrides such as borane, methane, ammonia, and water. It is an ionic material that is insoluble in organic solvents (although soluble in molten Na), consistent with the fact that H− ions do not exist in solution. Because of the insolubility of NaH, all reactions involving NaH occur at the surface of the solid. Basic properties and structure NaH is produced by the direct reaction of hydrogen and liquid sodium.Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. . Pure NaH is colorless, although samples generally appear grey. NaH is ca. 40% denser than Na (0.968 g/cm3). NaH, like LiH, KH, RbH, and CsH, adopts the NaCl crystal structure. In this motif, each Na+ ion is surrounded by six H ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TASF Reagent
The TASF reagent or tris(dimethylamino)sulfonium difluorotrimethylsilicate is a reagent in organic chemistry with structural formula (CH3)2N)3Ssup>+ 2Si(CH3)3sup>−. It is an anhydrous source of fluoride and is used to cleave silyl ether protective groups. Many other fluoride reagents are known, but few are truly anhydrous, because of the extraordinary basicity of "naked" F−. In TASF, the fluoride is masked as an adduct with the weak Lewis acid trimethylsilylfluoride (FSi(CH3)3). The sulfonium cation ((CH3)2N)3S+ is unusually non-electrophilic due to the electron-donating properties of the three (CH3)2N substituents. This compound is prepared from sulfur tetrafluoride: :3 (CH3)2NSi(CH3)3 + SF4 → 2 (CH3)3SiF + (CH3)2N)3Ssup>+ 2Si(CH3)3sup>− The colorless salt precipitates from the reaction solvent, diethyl ether. Structure The cation (CH3)2N)3Ssup>+ is a sulfonium ion. The S-N distances are 1.612 and 1.675 pm. The N-S-N angles are 99.6°. The anion is 2Si(CH ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
