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Trisoxazolines
Trisoxazolines (Often abbreviated TRISOX or TOX) are a class of tridentate, chiral ligands composed of three oxazoline rings. Despite being neutral they are able to form stable complexes with high oxidation state metals, such as rare earths, due to the chelate effect. The ligands have been investigated for molecular recognition and their complexes are used in asymmetric catalysts and polymerisation. Synthesis Trisoxazolines can either be synthesised directly, from suitable tripodal starting materials, or built up in a modular manner. These approaches can be used to give ligands of differing symmetries, with the direct synthesis route giving homochiral ligands with C3 rotational symmetry and the modular approach typically being used to give asymmetric compounds (C1 symmetry), which are either heterochiral or possess a mix of both chiral and achiral groups. These differences in symmetry can significantly effect the coordination chemistry of the ligands and the catalytic activity of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bisoxazoline Ligand
In chemistry, bis(oxazoline) ligands (often abbreviated BOX ligands) are a class of privileged chiral ligands containing two oxazoline rings. They are typically C2‑symmetric and exist in a wide variety of forms; with structures based around CH2 or pyridine linkers being particularly common (often generalised BOX and PyBOX respectively). The coordination complexes of bis(oxazoline) ligands are used in asymmetric catalysis. These ligands are examples of C2-symmetric ligands. Synthesis The synthesis of oxazoline rings is well established and in general proceeded via the cyclisation of a 2‑amino alcohol with any of a number of suitable functional groups. In the case of bis(oxazoline)s, synthesis is most conveniently achieved by using bi-functional starting materials; as this allows both rings to be produced at once. Of the materials suitable, dicarboxylic or dinitrile compounds are the most commonly available and hence the majority bis(oxazoline) ligands are produced from the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxazoline
Oxazoline is a five-membered heterocyclic organic compound with the formula . It is the parent of a family of compounds called oxazolines (emphasis on plural), which contain non-hydrogenic substituents on carbon and/or nitrogen. Oxazolines are the unsaturated analogues of oxazolidines, and they are isomeric with isoxazolines, where the N and O are directly bonded. Two isomers of oxazoline are known, depending on the location of the double bond. Oxazoline itself has no applications however oxazolines have been widely investigated for potential applications. These applications include use as ligands in asymmetric catalysis, as protecting groups for carboxylic acids and increasingly as monomers for the production of polymers. Isomers Synthesis The synthesis of 2-oxazoline rings is well established and in general proceeds via the cyclisation of a 2-amino alcohol (typically obtained by the reduction of an amino acid) with a suitable functional group. The overall mechanism is usual ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TBuLi
''tert''-Butyllithium is a chemical compound with the Chemical formula, formula (CH3)3CLi. As an organolithium compound, it has applications in organic synthesis since it is a strong Base (chemistry), base, capable of deprotonating many carbon molecules, including benzene. ''tert''-Butyllithium is available commercially as hydrocarbon solutions; it is not usually prepared in the laboratory. Preparation ''tert''-Butyllithium is produced commercially by treating ''tert''-butyl chloride with lithium metal. Its synthesis was first reported by R. B. Woodward in 1941. Structure and bonding : Like other organolithium compounds, ''tert''-butyllithium is a cluster compound. Whereas n-Butyllithium, ''n''-butyllithium exists both as a hexamer and a tetramer, ''tert''-butyllithium exists exclusively as a tetramer with a cubane-type cluster, cubane structure. Bonding in organolithium clusters involves Three-center two-electron bond, sigma delocalization and significant Li−Li bonding. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alpha-olefin
In organic chemistry, alpha-olefins (or α-olefins) are a family of organic compounds which are alkenes (also known as olefins) with a chemical formula , distinguished by having a double bond at the primary or alpha (α) position.''Petrochemicals in Nontechnical Language'', 3rd Edition, Donald L. Burdick and William L. Leffler, This location of a double bond enhances the reactivity of the compound and makes it useful for a number of applications. Classification There are two types of alpha-olefins, branched and linear (or normal). The chemical properties of branched alpha-olefins with a branch at either the second (vinylidene) or the third carbon number are significantly different from the properties of linear alpha-olefins and those with branches on the fourth carbon number and further from the start of the chain. Examples of linear alpha-olefins are propene, 1-butene and 1-decene. An example of a branched alpha-olefin is isobutylene. Production A variety of methods are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymerization
In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many forms of polymerization and different systems exist to categorize them. In chemical compounds, polymerization can occur via a variety of reaction mechanisms that vary in complexity due to the functional groups present in the reactants and their inherent steric effects. In more straightforward polymerizations, alkenes form polymers through relatively simple radical reactions; in contrast, reactions involving substitution at a carbonyl group require more complex synthesis due to the way in which reactants polymerize. Alkanes can also be polymerized, but only with the help of strong acids. As alkenes can polymerize in somewhat straightforward radical reactions, they form useful compounds such as polyethylene and polyvinyl chloride (PVC), w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Steric Bulk
Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivity of ions and molecules. Steric effects complement electronic effects, which dictate the shape and reactivity of molecules. Steric repulsive forces between overlapping electron clouds result in structured groupings of molecules stabilized by the way that opposites attract and like charges repel. Steric hindrance Steric hindrance is a consequence of steric effects. Steric hindrance is the slowing of chemical reactions due to steric bulk. It is usually manifested in ''intermolecular reactions'', whereas discussion of steric effects often focus on ''intramolecular interactions''. Steric hindrance is often exploited to control selectivity, such as slowing unwanted side-reactions. Steric hindrance between adjacent groups can also affect torsional ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Enantioselectivity
In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical antipode – is one of two stereoisomers that are non-superposable onto their own mirror image. Enantiomers are much like one's right and left hands, when looking at the same face, they cannot be superposed onto each other. No amount of reorientation will allow the four unique groups on the chiral carbon (see Chirality (chemistry)) to line up exactly. The number of stereoisomers a molecule has can be determined by the number of chiral carbons it has. Stereoisomers include both enantiomers and diastereomers. Diastereomers, like enantiomers, share the same molecular formula and are non-superposable onto each other however, they are not mirror images of each other. A molecule with chirality rotates plane-polarized light. A mixture of equals amo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solvent Effects
In chemistry, solvent effects are the influence of a solvent on chemical reactivity or molecular associations. Solvents can have an effect on solubility, stability and reaction rates and choosing the appropriate solvent allows for thermodynamic and kinetic control over a chemical reaction. A solute dissolves in a solvent when solvent-solute interactions are more favorable than solute-solute interaction. Effects on stability Different solvents can affect the equilibrium constant of a reaction by differential stabilization of the reactant or product. The equilibrium is shifted in the direction of the substance that is preferentially stabilized. Stabilization of the reactant or product can occur through any of the different non-covalent interactions with the solvent such as H-bonding, dipole-dipole interactions, van der Waals interactions etc. Acid-base equilibria The ionization equilibrium of an acid or a base is affected by a solvent change. The effect of the solvent is not on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Enantiomeric Excess
In stereochemistry, enantiomeric excess (ee) is a measurement of purity used for chiral substances. It reflects the degree to which a sample contains one enantiomer in greater amounts than the other. A racemic mixture has an ee of 0%, while a single completely pure enantiomer has an ee of 100%. A sample with 70% of one enantiomer and 30% of the other has an ee of 40% (70% − 30%). Definition Enantiomeric excess is defined as the absolute difference between the mole fraction of each enantiomer: :\ ee = , F_R - F_S, where :\ F_R + F_S = 1 In practice, it is most often expressed as a percent enantiomeric excess. The enantiomeric excess can be determined in another way if we know the amount of each enantiomer produced. If one knows the moles of each enantiomer produced then: Enantiomeric excess is used as one of the indicators of the success of an asymmetric synthesis. For mixtures of diastereomers, there are analogous definitions and uses for diastereomeric exces ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Indole
Indole is an aromatic heterocyclic organic compound with the formula C8 H7 N. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indole is widely distributed in the natural environment and can be produced by a variety of bacteria. As an intercellular signal molecule, indole regulates various aspects of bacterial physiology, including spore formation, plasmid stability, resistance to drugs, biofilm formation, and virulence. The amino acid tryptophan is an indole derivative and the precursor of the neurotransmitter serotonin. General properties and occurrence Indole is a solid at room temperature. It occurs naturally in human feces and has an intense fecal odor. At very low concentrations, however, it has a flowery smell, and is a constituent of many perfumes. It also occurs in coal tar. The corresponding substituent is called indolyl. Indole undergoes electrophilic substitution, mainly at position 3 (see diagr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Friedel–Crafts Reaction
The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring. Friedel–Crafts reactions are of two main types: alkylation reactions and acylation reactions. Both proceed by electrophilic aromatic substitution. Alkylation With alkyl halides Friedel–Crafts alkylation involves the alkylation of an aromatic ring. Traditionally, the alkylating agents are alkyl halides. Many alkylating agents can be used instead of alkyl halides. For example, enones and epoxides can be used in presence of protons. Traditionally also, the reaction employs a strong Lewis acid, such as aluminium chloride as catalyst. This reaction suffers from the disadvantage that the product is more nucleophilic than the reactant because alkyl groups are activators for the Friedel–Crafts reaction. Consequently, overalkylation can occur. Steric hindrance can be exploited to limit the number of alkylations, as in the ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
