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Macrocycle
Macrocycles are often described as molecules and ions containing a ring of twelve or more atoms. Classical examples include the crown ethers, calixarenes, porphyrins, and cyclodextrins. Macrocycles describe a large, mature area of chemistry. Synthesis The formation of macrocycles by ring-closure is called macrocyclization. The central challenge to macrocyclization is that ring-closing reactions do not favor the formation of large rings. Instead, medium sized rings or polymers tend to form. Early macrocyclizations were achieved ketonic decarboxylations for the preparation of terpenoid macrocycles. So, while Ružička was able to produce various macrocycles, the yields were low. This kinetic problem can be addressed by using high-dilution reactions, whereby intramolecular processes are favored relative to polymerizations. Reactions amenable to high dilution include Dieckmann condensation and related based-induced reactions of esters with remote halides. Some macrocyc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Porphyrin
Porphyrins ( ) are heterocyclic, macrocyclic, organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (). In vertebrates, an essential member of the porphyrin group is heme, which is a component of hemoproteins, whose functions include carrying oxygen in the bloodstream. In plants, an essential porphyrin derivative is chlorophyll, which is involved in light harvesting and electron transfer in photosynthesis. The parent of porphyrins is porphine, a rare chemical compound of exclusively theoretical interest. Substituted porphines are called porphyrins. With a total of 26 π-electrons the porphyrin ring structure is a coordinated aromatic system. One result of the large conjugated system is that porphyrins absorb strongly in the visible region of the electromagnetic spectrum, i.e. they are deeply colored. The name "porphyrin" derives . Structure Porphyrin complexes consist of a square planar MN4 core. The p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ring-closing Metathesis
Ring-closing metathesis (RCM) is a widely used variation of olefin metathesis in organic chemistry for the synthesis of various Saturated and unsaturated compounds, unsaturated rings via the intramolecular olefin metathesis, metathesis of two terminal alkenes, which forms the cycloalkene as the ''E-'' or ''Z-'' isomers and Volatility (chemistry), volatile ethylene.Carey, F. A.; Sunburg, R. J. Reactions Involving Transition Metals. ''Advanced Organic Chemistry: Reaction and Synthesis'', 5th Ed.; Part B; Springer: New York, 2010, pp. 761-767.Monfette, S.; Fogg, D. E. (2009). "Equilibrium Ring-Closing Metathesis". ''Chem. Rev.'' 109 (8): 3783-3816. . The most commonly synthesized ring sizes are between 5-7 atoms;Deiters, A.; Martin, S. F. (2004). “Synthesis of Oxygen- and Nitrogen-Containing Heterocycles by Ring-Closing Metathesis”. ''Chem. Rev.'' 104 (5): 2199-2238. . however, reported syntheses include 45- up to 90- membered macroheterocycles.Cain, M. F.; Forrest, W. P.; Pery ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Calixarene
A calixarene is a macrocycle or cyclic oligomer based on a methylene-linked phenols. With hydrophobic cavities that can hold smaller molecules or ions, calixarenes belong to the class of cavitands known in host–guest chemistry. Nomenclature Calixarene nomenclature is straightforward and involves counting the number of repeating units in the ring and including it in the name. A calix rene has 4 units in the ring and a calix rene has 6. A substituent in the meso position Rb is added to the name with a prefix C- as in C-methylcalix rene The word calixarene is derived from the Greek calix or chalice because this type of molecule resembles a vase (or cup) and from the word arene that refers to the aromatic building block. Synthesis Calixarenes are generally produced by condensation of two components: an electron-rich aromatic compound, classically a 4-substituted phenol, and an aldehyde, classically formaldehyde. *The scope for the aromatic component is broad diverse. The ke ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyclodextrin
Cyclodextrins are a family of cyclic oligosaccharides, consisting of a macrocycle, macrocyclic ring of glucose subunits joined by α-1,4 glycosidic bonds. Cyclodextrins are produced from starch by enzyme, enzymatic conversion. They are used in food, pharmaceutical, drug delivery, and chemical industries, as well as agriculture and environmental engineering. Cyclodextrins are composed of 5 or more α-D-glucoPyranose, pyranoside units linked 1 → 4, as in amylose (a fragment of starch). Typical cyclodextrins contain a number of glucose monomers ranging from six to eight units in a ring, creating a cone shape: * α-Cyclodextrin, α (alpha)-cyclodextrin: 6 glucose subunits * β-Cyclodextrin, β (beta)-cyclodextrin: 7 glucose subunits * γ-Cyclodextrin, γ (gamma)-cyclodextrin: 8 glucose subunits The largest well-characterized cyclodextrin contains 32 1,4-anhydroglucopyranoside units. Poorly-characterized mixtures, containing at least 150-membered cyclic oligosaccharides are also ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transannular
In organic chemistry, annulation (; occasionally annelation) is a chemical reaction in which a new ring is constructed on a molecule. : Examples are the Robinson annulation, Danheiser annulation and certain cycloadditions. Annular molecules are constructed from side-on condensed cyclic segments, for example helicenes and acenes. In transannulation a bicyclic molecule is created by intramolecular carbon-carbon bond formation in a large monocyclic ring. An example is the samarium(II) iodide induced ketone - alkene cyclization of ''5-methylenecyclooctanone'' which proceeds through a ketyl intermediate: : Benzannulation The term benzannulated compounds refers to derivatives of cyclic compounds (usually aromatic) which are fused to a benzene ring. Examples are listed in the table below: In contemporary chemical literature, the term benzannulation also means "construction of benzene rings from acyclic precursors". upright=1.4, Protonation of atrane.html" ;"title="Verkade base ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crown Ether
In organic chemistry, crown ethers are cyclic chemical compounds that consist of a ring containing several ether groups (). The most common crown ethers are cyclic oligomers of ethylene oxide, the repeating unit being ethyleneoxy, i.e., . Important members of this series are the tetramer (''n'' = 4), the pentamer (''n'' = 5), and the hexamer (''n'' = 6). The term "crown" refers to the resemblance between the structure of a crown ether bound to a cation, and a crown sitting on a person's head. The first number in a crown ether's name refers to the number of atoms in the cycle, and the second number refers to the number of those atoms that are oxygen. Crown ethers are much broader than the oligomers of ethylene oxide; an important group are derived from catechol. Crown ethers strongly bind certain cations, forming complexes. The oxygen atoms are well situated to coordinate with a cation located at the interior of the ring, whereas the exterior of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organic Chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistry''. Oxford University Press. pp. 1–15. . Study of structure determines their structural formula. Study of properties includes Physical property, physical and Chemical property, chemical properties, and evaluation of Reactivity (chemistry), chemical reactivity to understand their behavior. The study of organic reactions includes the organic synthesis, chemical synthesis of natural products, drugs, and polymers, and study of individual organic molecules in the laboratory and via theoretical (in silico) study. The range of chemicals studied chemistry includes hydrocarbons (compounds containing only carbon and hydrogen) as well as compounds based on carbon, but a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
High-dilution Reaction
In organic chemistry, the high dilution principle is a strategy for some macrocyclization reactions, i.e. the synthesis of macrocycles. Unlike the synthesis of 5- and 6-membered rings, the preparation of larger rings competes unfavorably with polymerization reactions. Polymers arise from coupling of long chain precursors. Such reactions are disfavored when the acyclic compounds are dilute. Although high dilution reactions can be conducted in a batch reactor with large volumes of solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ..., an alternative practical implementation entails slow addition of reactants, under conditions that the reactants are more rapidly consumed than the rate of addition. Typically, additions use one or more syringe pumps. Illustrative is the synthesis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Conformational Isomerism
In chemistry, rotamers are chemical species that differ from one another primarily due to rotations about one or more single bonds. Various arrangements of atoms in a molecule that differ by rotation about single bonds can also be referred to as conformations. Conformers/rotamers differ little in their energies, so they are almost never separable in a practical sense. Rotations about single bonds are subject to small energy barriers. When the time scale for interconversion is long enough for isolation of individual rotamers (usually arbitrarily defined as a half-life of interconversion of 1000 seconds or longer), the species are termed atropisomers (''see:'' atropisomerism). The Ring flip, ring-flip of substituted cyclohexanes constitutes a common form of conformers. The study of the energetics of bond rotation is referred to as conformational analysis. In some cases, conformational analysis can be used to predict and explain product selectivity, mechanisms, and rates of reaction ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Template Reaction
In chemistry, a template reaction is any of a class of ligand-based reactions that occur between two or more adjacent coordination sites on a metal center. In the absence of the metal ion, the same organic reactants produce different products. The term is mainly used in Complex (chemistry), coordination chemistry. The template effects emphasizes the pre-organization provided by the coordination sphere, although the coordination modifies the electronic properties (acidity, electrophilicity, etc.) of ligands. An early example is the dialkylation of a nickel dithiolate: : The corresponding alkylation in the absence of a metal ion would yield polymers. Crown ethers arise from dialkylations that are templated by alkali metals. Other template reactions include the Mannich reaction, Mannich and Schiff base condensations. The condensation of formaldehyde, ammonia, and tris(ethylenediamine)cobalt(III) to give a clathrochelate complex is one example. The phosphorus analogue of an aza cr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
