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Section: Photoredox enabled biocatalysis. Recently, photoredox catalysis has been applied to biocatalysis, enabling unique, previously inaccessible transformations. Photoredox chemistry relies upon light to generate free radical intermediates. These radical intermediates are achiral thus racemic mixtures of product are... | Wikipedia - Biocatalysis - Photoredox enabled biocatalysis | 340 | 1,564 | null |
Section: Didanosine. In 2014 the technique was used to produce the HIV drug didanosine: a simpler molecule was identified that can be converted into didanosine when subjected to a specific chemical transformation in the presence of a specific enzyme. The gene that creates the enzyme was then "copied", adding random mut... | Wikipedia - Bioretrosynthesis - Didanosine | 225 | 1,047 | null |
Section: Overview. A blocked isocyanate can be added to materials that would normally react with the isocyanate such as polyols. They do not react at normal ambient room temperature. A formulation containing a blocked isocyanate is a single component material (and thus usually considered more convenient) but reacts lik... | Wikipedia - Blocked isocyanates - Overview | 234 | 1,182 | null |
Section: Uses. Apart from uses in coatings and adhesives they are also used to enhance the performance of polyester tire cord. Other uses include Powder coatings, Coil Coatings, Cationic Electrocoating and primers. Blocked isocyanates have also been used in tertiary oilfield recovery techniques. A blocked isocyanate is... | Wikipedia - Blocked isocyanates - Uses | 166 | 758 | null |
Article: Bolaamphiphile. In chemistry, bolaamphiphiles (also known as bolaform surfactants, bolaphiles, or alpha-omega-type surfactants) are amphiphilic molecules that have hydrophilic groups at both ends of a sufficiently long hydrophobic hydrocarbon chain. Compared to single-headed amphiphiles, the introduction of a ... | Wikipedia - Bolaamphiphile - Summary | 169 | 687 | null |
Article: Branching (polymer chemistry). In polymer chemistry, branching is the regular or irregular attachment of side chains to a polymer's backbone chain. It occurs by the replacement of a substituent (e.g. a hydrogen atom) on a monomer subunit by another covalently-bonded chain of that polymer; or, in the case of a ... | Wikipedia - Branching (polymer chemistry) - Summary | 329 | 1,498 | null |
In fact, preventing branching to produce linear polyethylene requires special methods. Because of the way polyamides are formed, nylon would seem to be limited to unbranched, straight chains. But "star" branched nylon can be produced by the condensation of dicarboxylic acids with polyamines having three or more amino g... | Wikipedia - Branching (polymer chemistry) - Summary | 169 | 688 | null |
Section: Special types of branched polymer. A graft polymer molecule is a branched polymer molecule in which one or more of the side chains are different, structurally or configurationally, from the main chain. A star-shaped polymer molecule is a branched polymer molecule in which a single branch point gives rise to mu... | Wikipedia - Branching (polymer chemistry) - Special types of branched polymer | 230 | 1,143 | null |
Section: In radical polymerization. In free radical polymerization, branching occurs when a chain curls back and bonds to an earlier part of the chain. When this curl breaks, it leaves small chains sprouting from the main carbon backbone. Branched carbon chains cannot line up as close to each other as unbranched chains... | Wikipedia - Branching (polymer chemistry) - In radical polymerization | 347 | 1,671 | null |
Section: Branching index. The branching index measures the effect of long-chain branches on the size of a macromolecule in solution. It is defined as g = ⟨ s b 2 ⟩ ⟨ s l 2 ⟩ {\displaystyle g={\frac {\langle s_{b}^{2}\rangle }{\langle s_{l}^{2}\rangle }}} where sb is the mean square radius of gyration of the branched ma... | Wikipedia - Branching (polymer chemistry) - Branching index | 159 | 571 | null |
Article: Meta-selective C–H functionalization. Meta-selective C–H functionalization refers to the regioselective reaction of a substituted aromatic ring on the C–H bond meta to the substituent. Substituted aromatic ring is an important type of substructure in pharmaceuticals and industrial compounds. Thus, synthetic me... | Wikipedia - Meta-selective C–H functionalization - Summary | 333 | 1,654 | null |
Thus, while ortho-selectivity has been achieved by numerous catalytic systems, meta- and para-selectivity remains a challenge. In recent years, new strategies that override the electronic and steric bias have been developed to address meta-C–H functionalization. However, before these discoveries, synthesis of meta-subs... | Wikipedia - Meta-selective C–H functionalization - Summary | 224 | 1,169 | null |
Section: Recently-developed meta-selective C–H activation strategies > Copper catalyzed meta-selective C–H arylation. In 2009, Gaunt's group reported a copper catalyzed meta-selective C–H arylation reaction on anilide derivatives. Despite the intrinsic ortho-/para- selectivity of the amido group, the arylation occurs e... | Wikipedia - Meta-selective C–H functionalization - Recently-developed meta-selective C–H activation strategies > Copper catalyzed meta-selective C–H arylation | 326 | 1,408 | null |
The power of the meta-selectivity overrides the electronic effect of different substituents, including the strong ortho/para-directing m-methoxy group. Although the copper catalyzed meta-selective C–H arylation is quite successful, the mechanism behind the meta-selectivity is not completely understood. There are genera... | Wikipedia - Meta-selective C–H functionalization - Recently-developed meta-selective C–H activation strategies > Copper catalyzed meta-selective C–H arylation | 330 | 1,377 | null |
Section: Recently-developed meta-selective C–H activation strategies > Meta-selective C-H functionalization assisted by a remote "end-on" template. In 2012, Yu and co-workers reported a pioneering meta-selective C-H olefination using nitrile-containing templates to deliver the palladium to the meta-position via a macro... | Wikipedia - Meta-selective C–H functionalization - Recently-developed meta-selective C–H activation strategies > Meta-selective C-H functionalization assisted by a remote "end-on" template | 325 | 1,337 | null |
Section: Recently-developed meta-selective C–H activation strategies > Mechanism. The mechanistic study of the palladium-catalyzed meta-selective C–H bond activation with a nitrile-containing template was done by Yu, Wu, Houk and their co-workers. The DFT calculations suggest that the regioselectivity is achieved in th... | Wikipedia - Meta-selective C–H functionalization - Recently-developed meta-selective C–H activation strategies > Mechanism | 218 | 902 | null |
Section: Recently-developed meta-selective C–H activation strategies > Meta-alkylation achieved by remote ortho-ruthenation and electrophilic-type substitution. Originally discovered by Frost and co-workers, the meta selective sulfonation of 2-phenylpyridine using a sulfonyl chloride coupling partner, utilising a ruthe... | Wikipedia - Meta-selective C–H functionalization - Recently-developed meta-selective C–H activation strategies > Meta-alkylation achieved by remote ortho-ruthenation and electrophilic-type substitution | 216 | 904 | null |
Section: Properties. Similar to hydrogen bonds, a C–H···O interaction involves interactions of dipoles and therefore has directionality. The directionality of a C–H···O interaction is usually defined by the angle α between the С, Н and О atoms, and the distance d between the O and C atoms. In a С–Н···О interaction, the... | Wikipedia - C–H···O interaction - Properties | 266 | 1,047 | null |
Article: Carboboration. In organic chemistry, carboboration is an addition of both a carbon and a boron moiety to certain carbon-containing double and triple bonds, such as alkenes, alkynes, and allenes. In the synthesis of organic compounds, this chemical reaction is used to install a new carbon-carbon bond and carbon... | Wikipedia - Carboboration - Summary | 267 | 1,236 | null |
Section: 1,1 Carboboration. 1,1 carboboration delivers both the carbon-carbon bond and the carbon-boron bond to the same carbon in the substrate. It requires a 1,2-migration of a substituent from one carbon to the other in the double bond. The Wrackmeyer reaction is typically credited as being the pioneering example of... | Wikipedia - Carboboration - 1,1 Carboboration | 197 | 811 | null |
Section: 1,1 Carboboration > Mechanism. Wrackmeyer-type 1,1 carboboration is proposed to go through a zwitterionic intermediate, and this intermediate has been isolated and characterized in some cases. However, the mechanism can be highly substrate and reagent dependent. In a borane, the compound typically adopts a tri... | Wikipedia - Carboboration - 1,1 Carboboration > Mechanism | 295 | 1,267 | null |
Section: 1,2 Carboboration > Mechanism. The mechanism of carboboration depends highly on the substrate and reagents utilized in the reaction. Shown below are examples of two types of Pd-catalyzed alkene 1,2 carboborations, Heck-type and the Wacker-type. However, the Cu- and Ni-catalyzed reactions can proceed through si... | Wikipedia - Carboboration - 1,2 Carboboration > Mechanism | 300 | 1,308 | null |
Article: Carbodiimide. In organic chemistry, a carbodiimide (systematic IUPAC name: methanediimine) is a functional group with the formula RN=C=NR. On Earth they are exclusively synthetic, but in interstellar space the parent compound HN=C=NH has been detected by its maser emissions. A well known carbodiimide is dicycl... | Wikipedia - Carbodiimide - Summary | 176 | 721 | null |
Section: Structure and bonding. From the perspective of bonding, carbodiimides are isoelectronic with carbon dioxide. Three principal resonance structures describe carbodiimides: RN=C=NR ↔ RN+≡C-N−R ↔ RN−-C≡N+R The N=C=N core is relatively linear and the C-N=C angles approach 120°. In the case of C(NCHPh2)2, the centra... | Wikipedia - Carbodiimide - Structure and bonding | 286 | 1,098 | null |
Section: Synthesis > From thioureas and ureas. A classic route to carbodiimides involves dehydrosulfurization of thioureas. A typical reagent for this process is mercuric oxide: (R(H)N)2CS + HgO → (RN)2C + HgS + H2O This reaction can often be conducted as stated, even though carbodiimides react with water. In some case... | Wikipedia - Carbodiimide - Synthesis > From thioureas and ureas | 179 | 552 | null |
Section: Reactions > Coupling agents. In organic synthesis, compounds containing the carbodiimide functionality are used as dehydration agents. Specifically they are often used to convert carboxylic acids to amides or esters. Additives, such as N-hydroxybenzotriazole or N-hydroxysuccinimide, are often added to increase... | Wikipedia - Carbodiimide - Reactions > Coupling agents | 180 | 725 | null |
Section: Reactions > Coupling agents > Amide formation pathway. The formation of an amide using a carbodiimide is a common reaction, but carries the risk of several side reactions. The acid 1 will react with the carbodiimide to produce the key intermediate: the O-acylisourea 2, which can be viewed as a carboxylic ester... | Wikipedia - Carbodiimide - Reactions > Coupling agents > Amide formation pathway | 238 | 901 | null |
Section: Examples > DCC. DCC (acronym for N,N'-dicyclohexylcarbodiimide) was one of the first carbodiimides developed as a reagent. It is widely used for amide and ester formation, especially for solid-phase synthesis of peptides. DCC has achieved popularity mainly because of its high-yielding amide coupling reactions ... | Wikipedia - Carbodiimide - Examples > DCC | 204 | 875 | null |
Article: Carbon–carbon bond. A carbon–carbon bond is a covalent bond between two carbon atoms. The most common form is the single bond: a bond composed of two electrons, one from each of the two atoms. The carbon–carbon single bond is a sigma bond and is formed between one hybridized orbital from each of the carbon ato... | Wikipedia - Carbon–carbon bond - Summary | 216 | 918 | null |
Section: Chains and branching. Carbon is one of the few elements that can form long chains of its own atoms, a property called catenation. This coupled with the strength of the carbon–carbon bond gives rise to an enormous number of molecular forms, many of which are important structural elements of life, so carbon comp... | Wikipedia - Carbon–carbon bond - Chains and branching | 198 | 971 | null |
Section: Synthesis. Carbon–carbon bond-forming reactions are organic reactions in which a new carbon–carbon bond is formed. They are important in the production of many human-made chemicals such as pharmaceuticals and plastics. The reverse reaction, where a carbon-carbon bond is broken, is known as carbon-carbon bond a... | Wikipedia - Carbon–carbon bond - Synthesis | 155 | 785 | null |
Section: Extreme cases > Long, weak C–C single bonds. Various extreme cases have been identified where the C–C bond is elongated. In Gomberg's dimer, one C–C bond is rather long at 159.7 picometers. It is this bond that reversibly and readily breaks at room temperature in solution: In the even more congested molecule h... | Wikipedia - Carbon–carbon bond - Extreme cases > Long, weak C–C single bonds | 168 | 605 | null |
Article: Carbon-carbon bond activation. Carbon-carbon bond activation refers to the breaking of carbon-carbon bonds in organic molecules. This process is an important tool in organic synthesis, as it allows for the formation of new carbon-carbon bonds and the construction of complex organic molecules. However, C–C bond... | Wikipedia - Carbon-carbon bond activation - Summary | 211 | 979 | null |
Section: Examples of C-C bond activation. Due to the difficulty of C-C activation, a driving force is required to facilitate the reaction. One common strategy is to form stable metal complexes. One example is reported by Milstein and coworkers, in which the C(sp2)–C(sp3) bond of bisphosphine ligands was selectively cle... | Wikipedia - Carbon-carbon bond activation - Examples of C-C bond activation | 249 | 1,008 | null |
Section: Mechanism of C-C bond activation > β-carbon elimination. In 1997, Tamaru group reported the first metal-catalyzed β-carbon elimination of an unstrained compound. Their work revealed a novel Pd(0)-catalyzed ring opening of 4-vinyl cyclic carbonates. They proposed that the reaction is initiated by the eliminatio... | Wikipedia - Carbon-carbon bond activation - Mechanism of C-C bond activation > β-carbon elimination | 229 | 978 | null |
Section: Mechanism of C-C bond activation > Oxidative addition. Compared with β-carbon elimination, oxidative addition of C-C bond is a more direct way of C-C bond activation. However, it is more challenging to do for the following reasons: 1) It forms two weak M-C bonds at the expense of breaking a stable C-C bond, so... | Wikipedia - Carbon-carbon bond activation - Mechanism of C-C bond activation > Oxidative addition | 307 | 1,182 | null |
Section: Electronegativity and bond strength. The high electronegativity of fluorine (4.0 for fluorine vs. 2.5 for carbon) gives the carbon–fluorine bond a significant polarity or dipole moment. The electron density is concentrated around the fluorine, leaving the carbon relatively electron poor. This introduces ionic ... | Wikipedia - Carbon–fluorine bond - Electronegativity and bond strength | 264 | 999 | null |
Section: Bond length. The carbon–fluorine bond length is typically about 1.35 ångström (1.39 Å in fluoromethane). It is shorter than any other carbon–halogen bond, and shorter than single carbon–nitrogen and carbon–oxygen bonds. The short length of the bond can also be attributed to the ionic character of the bond (the... | Wikipedia - Carbon–fluorine bond - Bond length | 324 | 1,530 | null |
Section: Gauche effect. When two fluorine atoms are in vicinal (i.e., adjacent) carbons, as in 1,2-difluoroethane (H2FCCFH2), the gauche conformer is more stable than the anti conformer—this is the opposite of what would normally be expected and to what is observed for most 1,2-disubstituted ethanes; this phenomenon is... | Wikipedia - Carbon–fluorine bond - Gauche effect | 341 | 1,283 | null |
Due to the greater electronegativity of fluorine, the carbon–hydrogen σ orbital is a better electron donor than the carbon–fluorine σ orbital, while the carbon–fluorine σ* orbital is a better electron acceptor than the carbon–hydrogen σ* orbital. Only the gauche conformation allows good overlap between the better donor... | Wikipedia - Carbon–fluorine bond - Gauche effect | 198 | 898 | null |
Section: Spectroscopy. The carbon–fluorine bond stretching appears in the infrared spectrum between 1000 and 1360 cm−1. The wide range is due to the sensitivity of the stretching frequency to other substituents in the molecule. Monofluorinated compounds have a strong band between 1000 and 1110 cm−1; with more than one ... | Wikipedia - Carbon–fluorine bond - Spectroscopy | 200 | 890 | null |
Section: Breaking C–F bonds. Breaking C–F bonds is of interest as a way to decompose and destroy organofluorine "forever chemicals" such as PFOA and perfluorinated compounds (PFCs). Candidate methods include catalysts, such as platinum atoms; photocatalysts; UV, iodide, and sulfite, radicals; etc. Some metal complexes ... | Wikipedia - Carbon–fluorine bond - Breaking C–F bonds | 288 | 962 | null |
Article: Carbon–hydrogen bond. In chemistry, the carbon–hydrogen bond (C−H bond) is a chemical bond between carbon and hydrogen atoms that can be found in many organic compounds. This bond is a covalent, single bond, meaning that carbon shares its outer valence electrons with up to four hydrogens. This completes both o... | Wikipedia - Carbon–hydrogen bond - Summary | 325 | 1,358 | null |
Article: Carbon–hydrogen bond activation. In organic chemistry and organometallic chemistry, carbon–hydrogen bond activation (C−H activation) is a type of organic reaction in which a carbon–hydrogen bond is cleaved and replaced with a C−X bond (X ≠ H is typically a main group element, like carbon, oxygen, or nitrogen).... | Wikipedia - Carbon–hydrogen bond activation - Summary | 336 | 1,573 | null |
This broader definition encompasses all reactions that would fall under the restricted definition of C–H activation given above. However, it also includes iron-catalyzed alkane C–H hydroxylation reactions that proceed through the oxygen rebound mechanism (e.g. cytochrome P450 enzymes and their synthetic analogues), in ... | Wikipedia - Carbon–hydrogen bond activation - Summary | 340 | 1,426 | null |
Other mechanistic possibilities not involving direct C–H bond cleavage by the metal include (i) generation of arylmetal species by electrophilic aromatic substitution mechanism (common for electrophilic Pd, Pt, Au, Hg species), (ii) cleavage of the C–H bond via hydrogen atom abstraction by an O- or N-centered radical, ... | Wikipedia - Carbon–hydrogen bond activation - Summary | 270 | 1,141 | null |
Section: Classification. Mechanisms for C-H activation by metal centers can be classified into three general categories: (i) Oxidative addition, in which a low-valent metal center inserts into a carbon-hydrogen bond, which cleaves the bond and oxidizes the metal: LnM + RH → LnM(R)(H) (ii) Electrophilic activation in wh... | Wikipedia - Carbon–hydrogen bond activation - Classification | 219 | 814 | null |
Section: Historic overview. The first C–H activation reaction is often attributed to Otto Dimroth, who in 1902, reported that benzene reacted with mercury(II) acetate (See: organomercury). Many electrophilic metal centers undergo this Friedel-Crafts-like reaction. Joseph Chatt observed the addition of C-H bonds of naph... | Wikipedia - Carbon–hydrogen bond activation - Historic overview | 316 | 1,324 | null |
In some cases, discoveries in C-H activation were being made in conjunction with those of cross coupling. In 1969, Yuzo Fujiwara reported the synthesis of (E)-1,2-diphenylethene from benzene and styrene with Pd(OAc)2 and Cu(OAc)2, a procedure very similar to that of cross coupling. On the category of oxidative addition... | Wikipedia - Carbon–hydrogen bond activation - Historic overview | 316 | 1,150 | null |
W.A.G. Graham found that the same hydrocarbons react with Cp*Ir(CO)2 upon irradiation to afford the related alkylhydrido complexes Cp*Ir(CO)HR, where R = cyclohexyl and neopentyl, respectively. In the latter example, the reaction is presumed to proceed via the oxidative addition of alkane to a 16-electron iridium(I) in... | Wikipedia - Carbon–hydrogen bond activation - Historic overview | 333 | 1,173 | null |
Section: Mechanistic understanding. One approach to improving chemical reactions is the understanding of the underlying reaction mechanism. time-resolved spectroscopic techniques can be used to follow the dynamics of the chemical reaction. This technique requires a trigger for initiating the process, which is in most c... | Wikipedia - Carbon–hydrogen bond activation - Mechanistic understanding | 327 | 1,516 | null |
To answer the question of difference in reactivity for distinct complexes, the electronic structure of those needs to be investigated. This can be achieved by X-ray absorption spectroscopy (XAS) or resonant inelastic X-ray scattering (RIXS). These methods have been used to follow the steps of C-H activation with orbita... | Wikipedia - Carbon–hydrogen bond activation - Mechanistic understanding | 179 | 849 | null |
Section: Directed C-H activation. Directed-, chelation-assisted-, or "guided" C-H activation involves directing groups that influence regio- and stereochemistry. This is the most useful style of C-H activation in organic synthesis. N,N-dimethylbenzylamine undergoes cyclometalation readily by many transition metals. A s... | Wikipedia - Carbon–hydrogen bond activation - Directed C-H activation | 156 | 684 | null |
Section: Directed C-H activation > Borylation. Transforming C-H bonds into C-B bonds through borylation has been thoroughly investigated due to their utility in synthesis (i.e. for cross-coupling reactions). John F. Hartwig reported a highly regioselective arene and alkane borylation catalyzed by a rhodium complex. In ... | Wikipedia - Carbon–hydrogen bond activation - Directed C-H activation > Borylation | 150 | 674 | null |
Section: Natural gas. Although chemists have failed to develop a commercial process for selective C-H activation of methane, such a reaction is the basis of reverse methanogenesis. In this nickel-catalyzed process, methane is converted to the methyl substituent of coenzyme M, CH3SCH2CH2SO−3. Naturally occurring methane... | Wikipedia - Carbon–hydrogen bond activation - Natural gas | 225 | 1,003 | null |
Section: Asymmetric C–H functionalization. Rhodium-catalyzed carbene insertion reactions have been rendered enantioselective using chiral carboxylate ligands, notably the proline-derived DOSP ligand. The total synthesis of lithospermic acid employs guided C–H functionalization late stage to a highly functionalized syst... | Wikipedia - Carbon–hydrogen bond activation - Asymmetric C–H functionalization | 160 | 661 | null |
Section: Older reviews. Pre-2004 Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H. (1995). "Selective Intermolecular Carbon–Hydrogen Bond Activation by Synthetic Metal Complexes in Homogeneous Solution". Accounts of Chemical Research. 28 (3): 154–162. doi:10.1021/ar00051a009. Crabtree, R. H. (2001). "Alka... | Wikipedia - Carbon–hydrogen bond activation - Older reviews | 350 | 982 | null |
Y.; Mironov, O.; Jones, C.; Ziatdinov, V. R. (2004). "Perspectives on some challenges and approaches for developing the next generation of selective, low temperature, oxidation catalysts for alkane hydroxylation based on the C–H activation reaction". Journal of Molecular Catalysis A: Chemical. 220 (1): 7–25. doi:10.101... | Wikipedia - Carbon–hydrogen bond activation - Older reviews | 348 | 943 | null |
Boutadla, Y.; Davies, D. L.; Macgregor, S. A.; Poblador-Bahamonde, A. I. (2009). "Mechanisms of C–H bond activation: rich synergy between computation and experiment". Dalton Trans. 2009 (30): 5820–5831. doi:10.1039/B904967C. PMID 19623381. Wencel-Delord, J.; Dröge, T.; Liu, F.; Glorius, F. (2011). "Towards Mild Metal-C... | Wikipedia - Carbon–hydrogen bond activation - Older reviews | 346 | 830 | null |
(2010). "C–H Bond Activation in Transition Metal Species from a Computational Perspective". Chem. Rev. 110 (2): 749–823. doi:10.1021/cr900315k. PMID 20067255. 2012-2015 Hashiguchi, B. G.; Bischof, S. M.; Konnick, M. M.; Periana, R. A. (2012). "Designing Catalysts for Functionalization of Unactivated C–H Bonds Based on ... | Wikipedia - Carbon–hydrogen bond activation - Older reviews | 344 | 910 | null |
Article: Cascade reaction. A cascade reaction, also known as a domino reaction or tandem reaction, is a chemical process that comprises at least two consecutive reactions such that each subsequent reaction occurs only in virtue of the chemical functionality formed in the previous step. In cascade reactions, isolation o... | Wikipedia - Cascade reaction - Summary | 336 | 1,771 | null |
Since then, the use of cascade reactions has proliferated in the area of total synthesis. Similarly, the development of cascade-driven organic methodology has also grown tremendously. This increased interest in cascade sequences is reflected by the numerous relevant review articles published in the past couple of decad... | Wikipedia - Cascade reaction - Summary | 226 | 1,151 | null |
Section: Nucleophilic/electrophilic cascades. Nucleophilic/electrophilic cascades are defined as the cascade sequences in which the key step constitutes a nucleophilic or electrophilic attack. An example of such a cascade is seen in the short enantioselective synthesis of the broad-spectrum antibiotic (–)-chloramphenic... | Wikipedia - Cascade reaction - Nucleophilic/electrophilic cascades | 343 | 1,315 | null |
Section: Nucleophilic/electrophilic cascades > Organocatalytic cascades. A subcategory of nucleophilic/electrophilic sequences is constituted by organocatalytic cascades, in which the key nucleophilic attack is driven by organocatalysis. An organocatalytic cascade was employed in the total synthesis of the natural prod... | Wikipedia - Cascade reaction - Nucleophilic/electrophilic cascades > Organocatalytic cascades | 339 | 1,347 | null |
The transformation is mediated by the readily available proline-derived organocatalyst 23. The transformation was proposed to proceed via a Michael addition/Michael addition/aldol condensation sequence (Scheme 5). In the first step, Michael addition of aldehyde 20 to nitroalkene 21 occurs through enamine catalysis, yie... | Wikipedia - Cascade reaction - Nucleophilic/electrophilic cascades > Organocatalytic cascades | 163 | 688 | null |
Section: Radical cascades. Radical cascades are those in which the key step constitutes a radical reaction. The high reactivity of free radical species renders radical-based synthetic approaches decidedly suitable for cascade reactions. One of the most widely recognized examples of the synthetic utility of radical casc... | Wikipedia - Cascade reaction - Radical cascades | 344 | 1,451 | null |
Section: Pericyclic cascades. Possibly the most widely encountered kind of process in cascade transformations, pericyclic reactions include cycloadditions, electrocyclic reactions and sigmatropic rearrangements. Although some of the abovementioned instances of nucleophilic/electrophilic and radical cascades involved pe... | Wikipedia - Cascade reaction - Pericyclic cascades | 313 | 1,314 | null |
A pericyclic sequence involving intramolecular hetero-cycloaddition reactions was employed in the total synthesis of naturally occurring alkaloid (–)-vindorosine (Scheme 9). Rapid access to the target was achieved from a solution of 1,3,4-oxadiazole 44 in triisopropyl benzene subjected to high temperatures and reduced ... | Wikipedia - Cascade reaction - Pericyclic cascades | 335 | 1,354 | null |
Section: Transition-metal-catalyzed cascades. Transition-metal-catalyzed cascade sequences combine the novelty and power of organometallic chemistry with the synthetic utility and economy of cascade reactions, providing an even more ecologically and economically desirable approach to organic synthesis. For instance, rh... | Wikipedia - Cascade reaction - Transition-metal-catalyzed cascades | 310 | 1,284 | null |
An intramolecular [3+2] cycloaddition then spontaneously occurred to afford the target tigliane 66. The formal intramolecular [4+2] cycloaddition of 1,6-enynes of the type 67 mediated by gold catalysis is another example of a transition-metal-catalyzed cascade (Scheme 14). A variety of 1,6-enynes reacted under mild con... | Wikipedia - Cascade reaction - Transition-metal-catalyzed cascades | 309 | 1,244 | null |
An example of palladium-catalyzed cascades is represented by the asymmetric polyene Heck cyclization used in the preparation of (+)-xestoquinone from triflate substrate 75 (Scheme 16). Oxidative addition of the aryl–triflate bond into the palladium(0) complex in the presence of chiral diphosphine ligand (S)-binap yield... | Wikipedia - Cascade reaction - Transition-metal-catalyzed cascades | 208 | 825 | null |
Section: Multistep tandem reactions. Multistep tandem reactions (or cascade reactions) are a sequence of chemical transformations (usually more than two steps) that happens consecutively to convert a starting material to a complex product. This kind of organic reactions are designed to construct difficult structures en... | Wikipedia - Cascade reaction - Multistep tandem reactions | 305 | 1,415 | null |
Section: Carbon. Catenation occurs most readily with carbon, which forms covalent bonds with other carbon atoms to form long chains and structures. This is the reason for the presence of the vast number of organic compounds in nature. Carbon is most well known for its properties of catenation, with organic chemistry es... | Wikipedia - Catenation - Carbon | 332 | 1,655 | null |
Section: Hydrogen. Theories of the structure of water involve three-dimensional networks of tetrahedra and chains and rings, linked via hydrogen bonding. A polycatenated network, with rings formed from metal-templated hemispheres linked by hydrogen bonds, was reported in 2008. In organic chemistry, hydrogen bonding is ... | Wikipedia - Catenation - Hydrogen | 206 | 965 | null |
Section: Silicon. Silicon can form sigma bonds to other silicon atoms (and disilane is the parent of this class of compounds). However, it is difficult to prepare and isolate SinH2n+2 (analogous to the saturated alkane hydrocarbons) with n greater than about 8, as their thermal stability decreases with increases in the... | Wikipedia - Catenation - Silicon | 256 | 1,162 | null |
Article: Centralite. Ethyl centralite is an organic compound. Its chemical name is 1,3-diethyl-1,3-diphenylurea. The molecular formula of ethyl centralite is C17H20N2O. This compound has important uses in industry and forensics. The structure of ethyl centralite includes two phenyl groups (aromatic rings) attached to a... | Wikipedia - Centralite - Summary | 294 | 1,330 | null |
Section: Naming. The term "Centralite" was originally applied to dimethyldiphenylurea developed about 1906 at the German private military-industrial laboratory Zentralstelle für wissenschaftlich-technische Untersuchungen (Center for Scientific-Technical Research) in Neubabelsberg as a deterrent coating for smokeless po... | Wikipedia - Centralite - Naming | 157 | 721 | null |
Section: Synthesis. Ethyl centralite is also known as 1,3-diethyl-1,3-diphenylurea. It is synthesized through a chemical reaction. This reaction involves the condensation of aniline (C₆H₅NH₂) with ethyl isocyanate (C₂H₅NCO). The reaction typically occurs under controlled conditions. In this reaction, aniline reacts wit... | Wikipedia - Centralite - Synthesis | 292 | 1,091 | null |
Section: Applications > Smokeless powder. Burning rate moderator: Smokeless powder is a type of propellant used in firearms and ammunition. It burns in a more controlled and steady way. It produces less smoke and residue than traditional black powder. The burning rate of this powder is crucial for a firearm to work pro... | Wikipedia - Centralite - Applications > Smokeless powder | 346 | 1,746 | null |
Section: Applications > Forensic science. Gunshot Residue (GSR) Analysis: Ethyl centralite is important in forensic science. It is used to analyze gunshot residue (GSR). GSR is tiny particles that come out of a gun when it is fired. These particles can be found on the hands, clothes, or around the person who fired the ... | Wikipedia - Centralite - Applications > Forensic science | 250 | 1,142 | null |
Article: Chemical decomposition. Chemical decomposition, or chemical breakdown, is the process or effect of simplifying a single chemical entity (normal molecule, reaction intermediate, etc.) into two or more fragments. Chemical decomposition is usually regarded and defined as the exact opposite of chemical synthesis. ... | Wikipedia - Chemical decomposition - Summary | 338 | 1,787 | null |
Section: Reaction formula > Additional examples. An example of a spontaneous (without addition of an external energy source) decomposition is that of hydrogen peroxide which slowly decomposes into water and oxygen (see video at right): 2 H2O2 → 2 H2O + O2 This reaction is one of the exceptions to the endothermic nature... | Wikipedia - Chemical decomposition - Reaction formula > Additional examples | 342 | 1,565 | null |
Article: Chiral pool. The chiral pool is a "collection of abundant enantiopure building blocks provided by nature" used in synthesis. In other words, a chiral pool would be a large quantity of common organic enantiomers. Contributors to the chiral pool are amino acids, sugars, and terpenes. Their use improves the effic... | Wikipedia - Chiral pool - Summary | 174 | 823 | null |
Article: Cieplak effect. In organic chemistry, the Cieplak effect is a predictive model to rationalize why nucleophiles preferentially add to one face of a carbonyl over another. Proposed by Andrzej Stanislaw Cieplak in 1980, it correctly predicts results that could not be justified by the other standard models at the ... | Wikipedia - Cieplak effect - Summary | 245 | 1,043 | null |
Section: Background. The Cieplak effect relies on the stabilizing interaction of mixing full and empty orbitals to delocalize electrons, known as hyperconjugation. When the highest occupied molecular orbital (HOMO) of one system and the lowest unoccupied molecular orbital (LUMO) of another system have comparable energi... | Wikipedia - Cieplak effect - Background | 336 | 1,505 | null |
Reducing agents add a hydride to the carbonyl carbon via attack along the Burgi–Dunitz angle, which can come from the top along a pseudo-axial trajectory or from below, along a pseudo-equatorial trajectory. It has long been known that large reducing agents add hydride to the equatorial position to avoid steric interact... | Wikipedia - Cieplak effect - Background | 264 | 1,162 | null |
Section: Evidence. Cieplak's proposal is supported by investigating the effects of various electronic substituents on product distribution. By installing an electron-withdrawing substituent such as a methoxy group at the C2 position, the reduction of substituted cyclohexanones begins to favor equatorial attack. This is... | Wikipedia - Cieplak effect - Evidence | 350 | 1,513 | null |
In substituted norbornones, nucleophilic attack will come antiperiplanar to the bonds which can best donate into σ*C-Nuc. The bonds positioned for this interaction are the bridgehead C–C bonds on the six-membered ring. Substituents which donate electron density to these bonds, such as ethyl groups, increase the rate of... | Wikipedia - Cieplak effect - Evidence | 331 | 1,470 | null |
Section: Criticisms. The Cieplak model has been met with mixed reviews, and criticisms of both its basic logic and predictive ability have emerged. The stabilizing interaction of donating electron density into the transition state σ* orbital of a forming bond was immediately questioned, as this interaction has been wid... | Wikipedia - Cieplak effect - Criticisms | 302 | 1,475 | null |
Section: Alternative explanations. In an effort to explain the surprising stereoselectivities in the systems above, alternative explanations to the Cieplak effect have been proposed. In substituted cyclohexanones, the tendency of small reducing agents to add hydride axially is proposed to be caused by torsional strain ... | Wikipedia - Cieplak effect - Alternative explanations | 315 | 1,558 | null |
Article: Click chemistry. Click chemistry is an approach to chemical synthesis that emphasizes efficiency, simplicity, selectivity, and modularity in chemical processes used to join molecular building blocks. It includes both the development and use of "click reactions", a set of simple, biocompatible chemical reaction... | Wikipedia - Click chemistry - Summary | 263 | 1,303 | null |
Section: Principles. For a reaction to be considered a click reaction, it must satisfy certain characteristics: modularity insensitivity to solvent parameters high chemical yields insensitivity towards oxygen and water regiospecificity and stereospecificity a large thermodynamic driving force (>20 kcal/mol) to favor a ... | Wikipedia - Click chemistry - Principles | 197 | 954 | null |
Many of the click chemistry criteria are subjective, and even if measurable and objective criteria could be agreed upon, it is unlikely that any reaction will be perfect for every situation and application. However, several reactions have been identified that fit the concept better than others: [3+2] cycloadditions, su... | Wikipedia - Click chemistry - Principles | 240 | 971 | null |
Section: Specific Click Reactions > Copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The classic click reaction is the copper-catalyzed reaction of an azide with an alkyne to form a 5-membered heteroatom ring: a Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The first triazole synthesis, from diethyl acetyl... | Wikipedia - Click chemistry - Specific Click Reactions > Copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) | 309 | 1,066 | null |
The copper-catalyzed version of this reaction gives only the 1,4-isomer, whereas Huisgen's non-catalyzed 1,3-dipolar cycloaddition gives both the 1,4- and 1,5-isomers, is slow, and requires a temperature of 100 degrees Celsius. Moreover, this copper-catalyzed "click" does not require ligands on the metal, although acce... | Wikipedia - Click chemistry - Specific Click Reactions > Copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) | 308 | 1,305 | null |
Solutions to this problem have been presented, such as using water-soluble ligands on the copper to enhance cell penetration of the catalyst and thereby reduce the dosage needed, or to use chelating ligands to further increase the effective concentration of Cu(I) and thereby decreasing the actual dosage. Although the C... | Wikipedia - Click chemistry - Specific Click Reactions > Copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) | 243 | 1,200 | null |
Section: Specific Click Reactions > Strain-promoted azide-alkyne cycloaddition (SPAAC). The Bertozzi group further developed one of Huisgen's copper-free click reactions to overcome the cytotoxicity of the CuAAC reaction. Instead of using Cu(I) to activate the alkyne, the alkyne is instead introduced in a strained difl... | Wikipedia - Click chemistry - Specific Click Reactions > Strain-promoted azide-alkyne cycloaddition (SPAAC) | 295 | 1,149 | null |
Section: Specific Click Reactions > Strain-promoted alkyne-nitrone cycloaddition (SPANC). Diaryl-strained-cyclooctynes including dibenzylcyclooctyne (DIBO) have also been used to react with 1,3-nitrones in strain-promoted alkyne-nitrone cycloadditions (SPANC) to yield N-alkylated isoxazolines. Because this reaction is ... | Wikipedia - Click chemistry - Specific Click Reactions > Strain-promoted alkyne-nitrone cycloaddition (SPANC) | 344 | 1,302 | null |
Section: Specific Click Reactions > Reactions of strained alkenes > Alkene and azide [3+2] cycloaddition. Oxanorbornadiene (or another activated alkene) reacts with azides, giving triazoles as a product. However, these product triazoles are not aromatic as they are in the CuAAC or SPAAC reactions, and as a result are n... | Wikipedia - Click chemistry - Specific Click Reactions > Reactions of strained alkenes > Alkene and azide [3+2] cycloaddition | 177 | 695 | null |
Section: Specific Click Reactions > Reactions of strained alkenes > Alkene and tetrazine inverse-demand Diels-Alder. Strained cyclooctenes and other activated alkenes react with tetrazines in an inverse electron-demand Diels-Alder followed by a retro [4+2] cycloaddition (see figure). Like the other reactions of the tra... | Wikipedia - Click chemistry - Specific Click Reactions > Reactions of strained alkenes > Alkene and tetrazine inverse-demand Diels-Alder | 251 | 970 | null |
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