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Section: Reaction in presence of water. An alternative classification with broader scope is suggested by Yujiro Hayashi as he describes certain organocatalytic Aldol reactions as taking place in the presence of water. The observed effect in these reactions is not rate acceleration (that would be on water), but an incre... | Wikipedia - On-water reaction - Reaction in presence of water | 196 | 982 | null |
Article: Organic compound. Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-containing compounds such as alkanes (e.g. methane CH4) ... | Wikipedia - Organic compound - Summary | 308 | 1,487 | null |
Although organic compounds make up only a small percentage of Earth's crust, they are of central importance because all known life is based on organic compounds. Living things incorporate inorganic carbon compounds into organic compounds through a network of processes (the carbon cycle) that begins with the conversion ... | Wikipedia - Organic compound - Summary | 190 | 1,073 | null |
Section: History > Vitalism. Vitalism was a widespread conception that substances found in organic nature are formed from the chemical elements by the action of a "vital force" or "life-force" (vis vitalis) that only living organisms possess. In the 1810s, Jöns Jacob Berzelius argued that a regulative force must exist ... | Wikipedia - Organic compound - History > Vitalism | 291 | 1,458 | null |
Section: History > Modern classification and ambiguities. Although vitalism has been discredited, scientific nomenclature retains the distinction between organic and inorganic compounds. The modern meaning of organic compound is any compound that contains a significant amount of carbon—even though many of the organic c... | Wikipedia - Organic compound - History > Modern classification and ambiguities | 338 | 1,633 | null |
B4C and SiC, and graphite intercalation compounds, e.g. KC8). Other compounds and materials that are considered 'inorganic' by most authorities include: metal carbonates, simple oxides of carbon (CO, CO2, and arguably, C3O2), the allotropes of carbon, cyanide derivatives not containing an organic residue (e.g., KCN, (C... | Wikipedia - Organic compound - History > Modern classification and ambiguities | 347 | 1,289 | null |
Nickel tetracarbonyl is typically classified as an organometallic compound as it satisfies the broad definition that organometallic chemistry covers all compounds that contain at least one carbon to metal covalent bond; it is unknown whether organometallic compounds form a subset of organic compounds. For example, the ... | Wikipedia - Organic compound - History > Modern classification and ambiguities | 337 | 1,579 | null |
Mellitic acid, which contains no C–H bonds, is considered a possible organic compound in Martian soil. Terrestrially, it, and its anhydride, mellitic anhydride, are associated with the mineral mellite (Al2C6(COO)6·16H2O). A slightly broader definition of the organic compound includes all compounds bearing C–H or C–C bo... | Wikipedia - Organic compound - History > Modern classification and ambiguities | 162 | 657 | null |
Section: Soil organic matter. The organic matter in soil derives from plants, animals and microorganisms. In a forest, for example, leaf litter and woody materials fall to the forest floor. This is sometimes referred to as organic material. When it decays to the point in which it is no longer recognizable, it is called... | Wikipedia - Organic matter - Soil organic matter | 346 | 1,739 | null |
Section: Soil organic matter > Priming effect. The priming effect is characterized by intense changes in the natural process of soil organic matter (SOM) turnover, resulting from relatively moderate intervention with the soil. The phenomenon is generally caused by either pulsed or continuous changes to inputs of fresh ... | Wikipedia - Organic matter - Soil organic matter > Priming effect | 338 | 1,713 | null |
Löhnis was the first to discover the priming effect phenomenon in 1926 through his studies of green manure decomposition and its effects on legume plants in soil. He noticed that when adding fresh organic residues to the soil, it resulted in intensified mineralization by the humus N. It was not until 1953, though, that... | Wikipedia - Organic matter - Soil organic matter > Priming effect | 319 | 1,617 | null |
Section: Decomposition. One suitable definition of organic matter is biological material in the process of decaying or decomposing, such as humus. A closer look at the biological material in the process of decaying reveals so-called organic compounds (biological molecules) in the process of breaking up (disintegrating)... | Wikipedia - Organic matter - Decomposition | 242 | 1,348 | null |
Section: Organic chemistry. Measurements of organic matter generally measure only organic compounds or carbon, and so are only an approximation of the level of once living or decomposed matter. Some definitions of organic matter likewise only consider "organic matter" to refer to only the carbon content or organic comp... | Wikipedia - Organic matter - Organic chemistry | 348 | 1,755 | null |
Section: Aquatic > Water purification. The same capability of natural organic matter that helps with water retention in the soil creates problems for current water purification methods. In water, organic matter can still bind to metal ions and minerals. The purification process does not necessarily stop these bound mol... | Wikipedia - Organic matter - Aquatic > Water purification | 243 | 1,160 | null |
Section: History. Early examples were often uncovered by the observation of precipitates or color changes from samples that were exposed to sunlights. The first reported case was by Ciamician that sunlight converted santonin to a yellow photoproduct: An early example of a precipitate was the photodimerization of anthra... | Wikipedia - Organic photochemistry - History | 272 | 1,209 | null |
Section: Key reactions. Organic photochemical reactions are explained in the context of the relevant excited states. Parallel to the structural studies described above, the role of spin multiplicity – singlet vs triplet – on reactivity was evaluated. The importance of triplet excited species was emphasized. Triplets te... | Wikipedia - Organic photochemistry - Key reactions | 282 | 1,133 | null |
Section: Practical considerations. Reactants of the photoreactions can be both gaseous and liquids. In general, it is necessary to bring the reactants close to the light source in order to obtain the highest possible luminous efficacy. For this purpose, the reaction mixture can be irradiated either directly or in a flo... | Wikipedia - Organic photochemistry - Practical considerations | 348 | 1,805 | null |
Section: Case studies > 4,4-diphenylcyclohexenone. To provide further evidence on the mechanism of the dienone in which there is bonding between the two double bonds, the case of 4,4-diphenylcyclohexenone is presented here. It is seen that the rearrangement is quite different; thus two double bonds are required for a t... | Wikipedia - Organic photochemistry - Case studies > 4,4-diphenylcyclohexenone | 207 | 820 | null |
Section: Related topics > Photochlorination. Photochlorination is one of the largest implementations of photochemistry to organic synthesis. The photon is however not absorbed by the organic compound, but by chlorine. Photolysis of Cl2 gives chlorine atoms, which abstract H atoms from hydrocarbons, leading to chlorinat... | Wikipedia - Organic photochemistry - Related topics > Photochlorination | 294 | 807 | null |
Article: Organic reaction. Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical reactions and redox reactions. In organic synthe... | Wikipedia - Organic reaction - Summary | 177 | 936 | null |
Section: Classifications. Organic chemistry has a strong tradition of naming a specific reaction to its inventor or inventors and a long list of so-called named reactions exists, conservatively estimated at 1000. A very old named reaction is the Claisen rearrangement (1912) and a recent named reaction is the Bingel rea... | Wikipedia - Organic reaction - Classifications | 345 | 1,611 | null |
Radical reactions are characterized by species with unpaired electrons (radicals) and the movement of single electrons. Radical reactions are further divided into chain and nonchain processes. Finally, pericyclic reactions involve the redistribution of chemical bonds along a cyclic transition state. Although electron p... | Wikipedia - Organic reaction - Classifications | 173 | 986 | null |
Section: Fundamentals. Factors governing organic reactions are essentially the same as that of any chemical reaction. Factors specific to organic reactions are those that determine the stability of reactants and products such as conjugation, hyperconjugation and aromaticity and the presence and stability of reactive in... | Wikipedia - Organic reaction - Fundamentals | 216 | 1,082 | null |
Section: By mechanism. There is no limit to the number of possible organic reactions and mechanisms. However, certain general patterns are observed that can be used to describe many common or useful reactions. Each reaction has a stepwise reaction mechanism that explains how it happens, although this detailed descripti... | Wikipedia - Organic reaction - By mechanism | 230 | 1,289 | null |
Section: Other classification. In heterocyclic chemistry, organic reactions are classified by the type of heterocycle formed with respect to ring-size and type of heteroatom. See for instance the chemistry of indoles. Reactions are also categorized by the change in the carbon framework. Examples are ring expansion and ... | Wikipedia - Organic reaction - Other classification | 160 | 798 | null |
Article: Organocatalysis. In organic chemistry, organocatalysis is a form of catalysis in which the rate of a chemical reaction is increased by an organic catalyst. This "organocatalyst" consists of carbon, hydrogen, sulfur and other nonmetal elements found in organic compounds. Because of their similarity in compositi... | Wikipedia - Organocatalysis - Summary | 347 | 1,614 | null |
Section: Introduction. Regular achiral organocatalysts are based on nitrogen such as piperidine used in the Knoevenagel condensation. DMAP used in esterifications and DABCO used in the Baylis-Hillman reaction. Thiazolium salts are employed in the Stetter reaction. These catalysts and reactions have a long history but c... | Wikipedia - Organocatalysis - Introduction | 344 | 1,452 | null |
Section: Organocatalyst classes. Organocatalysts for asymmetric synthesis can be grouped in several classes: Biomolecules: proline, phenylalanine. Secondary amines in general. The cinchona alkaloids, certain oligopeptides. Synthetic catalysts derived from biomolecules. Hydrogen bonding catalysts, including TADDOLS, der... | Wikipedia - Organocatalysis - Organocatalyst classes | 163 | 664 | null |
Section: Imidazolidinone organocatalysis. Imidazolidinones are catalysts for many transformations such as asymmetric Diels-Alder reactions and Michael additions. Chiral catalysts induce asymmetric reactions, often with high enantioselectivities. This catalyst works by forming an iminium ion with carbonyl groups of α,β-... | Wikipedia - Organocatalysis - Imidazolidinone organocatalysis | 279 | 1,151 | null |
Section: Thiourea organocatalysis. A large group of organocatalysts incorporate the urea or the thiourea moiety. These catalytically effective (thio)urea derivatives termed (thio)urea organocatalysts provide explicit double hydrogen-bonding interactions to coordinate and activate H-bond accepting substrates. Their curr... | Wikipedia - Organocatalysis - Thiourea organocatalysis | 169 | 737 | null |
Article: Ortho effect. Ortho effect is an organic chemistry phenomenon where the presence of a chemical group at the at ortho position or the 1 and 2 position of a phenyl ring, relative to the carboxylic compound changes the chemical properties of the compound. This is caused by steric effects and bonding interactions ... | Wikipedia - Ortho effect - Summary | 219 | 1,086 | null |
Section: Ortho substituted aniline. When any group is present at ortho position to an amide group (NH2) in aniline then the basic character of that compound becomes weaker. For example, see the order of basicity of following substituted aniline:- p-Toluidine > m-Toluidine > Aniline > o-Toluidine Aniline > m-Nitroanilin... | Wikipedia - Ortho effect - Ortho substituted aniline | 270 | 910 | null |
Section: Electrophilic aromatic substitution of disubstituted benzene compounds. The ortho effect also occurs when a meta-directing group is positioned in a meta arrangement relative to an ortho–para-directing group, a new substituent introduced into the molecule tends to preferentially occupy the ortho position relati... | Wikipedia - Ortho effect - Electrophilic aromatic substitution of disubstituted benzene compounds | 285 | 1,057 | null |
As witnessed in the above example, when a π-acceptor substituent (πAS) is meta to a π-donor substituent (πDS), the electrophilic aromatic nitration occurs ortho to the πAS rather than para. Similar results were also observed on the nitration of 3-methylbenzoic acid in which 5-methyl-2-nitrobenzoic acid and 3-methyl-2-n... | Wikipedia - Ortho effect - Electrophilic aromatic substitution of disubstituted benzene compounds | 218 | 716 | null |
Article: Peptidomimetic. A peptidomimetic is a small protein-like chain designed to mimic a peptide. They typically arise either from modification of an existing peptide, or by designing similar systems that mimic peptides, such as peptoids and β-peptides. Irrespective of the approach, the altered chemical structure is... | Wikipedia - Peptidomimetic - Summary | 263 | 1,282 | null |
Section: Uses and examples. The use of peptides as drugs has some disadvantages because of their bioavailability and biostability. Rapid degradation, poor oral availability, difficult transportation through cell membranes, nonselective receptor binding, and challenging multistep preparation are the major limitations of... | Wikipedia - Peptidomimetic - Uses and examples | 325 | 1,348 | null |
In 2004, Walensky and co-workers reported a stabilized alpha helical peptide that mimics pro-apoptotic BH3-only proteins, such as BID and BAD. This molecule was designed to stabilize the native helical structure by forming a macrocycle between side chains that are not involved in binding. This process, referred to as p... | Wikipedia - Peptidomimetic - Uses and examples | 344 | 1,418 | null |
Section: Synthesis. For assembly, a purified amphiphilic polypeptoid of specific sequence is dissolved in aqueous solution. These form a monolayer (Langmuir–Blodgett film) on the air-water interface with their hydrophobic side chains oriented in air and hydrophilic side chains in the water. When this mono-layer is shru... | Wikipedia - Peptoid nanosheet - Synthesis | 234 | 1,003 | null |
Article: Phosphonium coupling. In organic chemistry, phosphonium coupling is a cross-coupling reaction for organic synthesis. It is a mild, efficient, chemoselective and versatile methodology for the formation of C–C, C–N, C–O, and C–S bond of unactivated and unprotected tautomerizable heterocycles. The method was orig... | Wikipedia - Phosphonium coupling - Summary | 248 | 1,002 | null |
Section: Application. Physical organic chemists use theoretical and experimental approaches work to understand these foundational problems in organic chemistry, including classical and statistical thermodynamic calculations, quantum mechanical theory and computational chemistry, as well as experimental spectroscopy (e.... | Wikipedia - Physical organic chemistry - Application | 153 | 778 | null |
Section: Scope. Physical organic chemistry is the study of the relationship between structure and reactivity of organic molecules. More specifically, physical organic chemistry applies the experimental tools of physical chemistry to the study of the structure of organic molecules and provides a theoretical framework th... | Wikipedia - Physical organic chemistry - Scope | 182 | 1,081 | null |
Section: Chemical structure and thermodynamics > Thermochemistry. Organic chemists use the tools of thermodynamics to study the bonding, stability, and energetics of chemical systems. This includes experiments to measure or determine the enthalpy (ΔH), entropy (ΔS), and Gibbs' free energy (ΔG) of a reaction, transforma... | Wikipedia - Physical organic chemistry - Chemical structure and thermodynamics > Thermochemistry | 294 | 1,281 | null |
Section: Chemical structure and thermodynamics > Conformational analysis. One of the primary methods for evaluating chemical stability and energetics is conformational analysis. Physical organic chemists use conformational analysis to evaluate the various types of strain present in a molecule to predict reaction produc... | Wikipedia - Physical organic chemistry - Chemical structure and thermodynamics > Conformational analysis | 347 | 1,700 | null |
Section: Chemical structure and thermodynamics > Non-covalent interactions. Chemists use the study of intramolecular and intermolecular non-covalent bonding/interactions in molecules to evaluate reactivity. Such interactions include, but are not limited to, hydrogen bonding, electrostatic interactions between charged m... | Wikipedia - Physical organic chemistry - Chemical structure and thermodynamics > Non-covalent interactions | 259 | 1,262 | null |
Section: Chemical structure and thermodynamics > Acid–base chemistry. The properties of acids and bases are relevant to physical organic chemistry. Organic chemists are primarily concerned with Brønsted–Lowry acids/bases as proton donors/acceptors and Lewis acids/bases as electron acceptors/donors in organic reactions.... | Wikipedia - Physical organic chemistry - Chemical structure and thermodynamics > Acid–base chemistry | 177 | 906 | null |
Section: Kinetics. Physical organic chemists use the mathematical foundation of chemical kinetics to study the rates of reactions and reaction mechanisms. Unlike thermodynamics, which is concerned with the relative stabilities of the products and reactants (ΔG°) and their equilibrium concentrations, the study of kineti... | Wikipedia - Physical organic chemistry - Kinetics | 170 | 842 | null |
Section: Kinetics > Rate laws. The study of chemical kinetics is used to determine the rate law for a reaction. The rate law provides a quantitative relationship between the rate of a chemical reaction and the concentrations or pressures of the chemical species present. Rate laws must be determined by experimental meas... | Wikipedia - Physical organic chemistry - Kinetics > Rate laws | 170 | 913 | null |
Section: Kinetics > Kinetic isotope effect. Although a rate law provides the stoichiometry of the transition state structure, it does not provide any information about breaking or forming bonds. The substitution of an isotope near a reactive position often leads to a change in the rate of a reaction. Isotopic substitut... | Wikipedia - Physical organic chemistry - Kinetics > Kinetic isotope effect | 168 | 915 | null |
Section: Kinetics > Substituent effects. The study of how substituents affect the reactivity of a molecule or the rate of reactions is of significant interest to chemists. Substituents can exert an effect through both steric and electronic interactions, the latter of which include resonance and inductive effects. The p... | Wikipedia - Physical organic chemistry - Kinetics > Substituent effects | 348 | 1,674 | null |
Section: Kinetics > Solvent effects. Solvents can have a powerful effect on solubility, stability, and reaction rate. A change in solvent can also allow a chemist to influence the thermodynamic or kinetic control of the reaction. Reactions proceed at different rates in different solvents due to the change in charge dis... | Wikipedia - Physical organic chemistry - Kinetics > Solvent effects | 334 | 1,531 | null |
Section: Quantum chemistry. Many aspects of the structure-reactivity relationship in organic chemistry can be rationalized through resonance, electron pushing, induction, the eight electron rule, and s-p hybridization, but these are only helpful formalisms and do not represent physical reality. Due to these limitations... | Wikipedia - Physical organic chemistry - Quantum chemistry | 330 | 1,815 | null |
For this reason, nuclei are of negligible size in relation to much lighter electrons and are treated as point charges in practical applications of quantum chemistry. Due to complex interactions which arise from electron-electron repulsion, algebraic solutions of the Schrödinger equation are only possible for systems wi... | Wikipedia - Physical organic chemistry - Quantum chemistry | 326 | 1,685 | null |
Similarly, the true electronic structure of 1,3-butadiene shows delocalized π-bonding molecular orbitals stretching through the entire molecule rather than two isolated double bonds as predicted by a simple Lewis structure. A complete electronic structure offers great predictive power for organic transformations and dy... | Wikipedia - Physical organic chemistry - Quantum chemistry | 346 | 1,745 | null |
Section: Spectroscopy, spectrometry, and crystallography. Physical organic chemistry often entails the identification of molecular structure, dynamics, and the concentration of reactants in the course of a reaction. The interaction of molecules with light can afford a wealth of data about such properties through nondes... | Wikipedia - Physical organic chemistry - Spectroscopy, spectrometry, and crystallography | 178 | 934 | null |
Section: Spectroscopy, spectrometry, and crystallography > NMR and EPR spectroscopy. One of the most powerful tools in physical organic chemistry is NMR spectroscopy. An external magnetic field applied to a paramagnetic nucleus generates two discrete states, with positive and negative spin values diverging in energy; t... | Wikipedia - Physical organic chemistry - Spectroscopy, spectrometry, and crystallography > NMR and EPR spectroscopy | 321 | 1,719 | null |
Section: Spectroscopy, spectrometry, and crystallography > Vibrational spectroscopy. Vibrational spectroscopy, or infrared (IR) spectroscopy, allows for the identification of functional groups and, due to its low expense and robustness, is often used in teaching labs and the real-time monitoring of reaction progress in... | Wikipedia - Physical organic chemistry - Spectroscopy, spectrometry, and crystallography > Vibrational spectroscopy | 331 | 1,822 | null |
Section: Spectroscopy, spectrometry, and crystallography > Electronic excitation spectroscopy. Electronic excitation spectroscopy, or ultraviolet-visible (UV-vis) spectroscopy, is performed in the visible and ultraviolet regions of the electromagnetic spectrum and is useful for probing the difference in energy between ... | Wikipedia - Physical organic chemistry - Spectroscopy, spectrometry, and crystallography > Electronic excitation spectroscopy | 159 | 865 | null |
Section: Spectroscopy, spectrometry, and crystallography > Electronic excitation spectroscopy > Mass spectrometry. Mass spectrometry is a technique which allows for the measurement of molecular mass and offers complementary data to spectroscopic techniques for structural identification. In a typical experiment a gas ph... | Wikipedia - Physical organic chemistry - Spectroscopy, spectrometry, and crystallography > Electronic excitation spectroscopy > Mass spectrometry | 316 | 1,699 | null |
Section: Spectroscopy, spectrometry, and crystallography > Electronic excitation spectroscopy > Crystallography. Unlike spectroscopic methods, X-ray crystallography always allows for unambiguous structure determination and provides precise bond angles and lengths totally unavailable through spectroscopy. It is often us... | Wikipedia - Physical organic chemistry - Spectroscopy, spectrometry, and crystallography > Electronic excitation spectroscopy > Crystallography | 302 | 1,568 | null |
Article: Pi electron donor-acceptor. The pEDA parameter (pi electron donor-acceptor) is a pi-electron substituent effect scale, described also as mesomeric or resonance effect. There is also a complementary scale - sEDA. The more positive is the value of pEDA the more pi-electron donating is a substituent. The more neg... | Wikipedia - Pi electron donor-acceptor - Summary | 342 | 1,412 | null |
Article: Pi-stacking. In chemistry, pi stacking (also called π–π stacking) refers to the presumptively attractive, noncovalent pi interactions between the pi bonds of aromatic rings, because of orbital overlap. According to some authors direct stacking of aromatic rings (the "sandwich interaction") is electrostatically... | Wikipedia - Pi-stacking - Summary | 323 | 1,756 | null |
Section: Evidence against pi stacking. The benzene dimer is the prototypical system for the study of pi stacking, and is experimentally bound by 8–12 kJ/mol (2–3 kcal/mol) in the gas phase with a separation of 4.96 Å between the centers of mass for the T-shaped dimer. The small binding energy makes the benzene dimer di... | Wikipedia - Pi-stacking - Evidence against pi stacking | 224 | 1,017 | null |
Section: Benzene dimers and related species. The preferred geometries of the benzene dimer have been modeled at a high level of theory with MP2-R12/A computations and very large counterpoise-corrected aug-cc-PVTZ basis sets. The two most stable conformations are the parallel displaced and T-shaped, which are essentiall... | Wikipedia - Pi-stacking - Benzene dimers and related species | 347 | 1,609 | null |
Section: Benzene dimers and related species > Electrostatic model. An early model for the role of substituents in pi stacking interactions was proposed by Hunter and Sanders. They used a simple mathematical model based on sigma and pi atomic charges, relative orientations, and van der Waals interactions to qualitativel... | Wikipedia - Pi-stacking - Benzene dimers and related species > Electrostatic model | 329 | 1,669 | null |
Hunter et al. applied a more sophisticated chemical double mutant cycle with a hydrogen-bonded "zipper" to the issue of substituent effects in pi stacking interactions. This technique has been used to study a multitude of noncovalent interactions. The single mutation, in this case changing a substituent on an aromatic ... | Wikipedia - Pi-stacking - Benzene dimers and related species > Electrostatic model | 306 | 1,561 | null |
Section: Benzene dimers and related species > Direct interaction model. The Hunter–Sanders model has been criticized by numerous research groups offering contradictory experimental and computational evidence of pi stacking interactions that are not governed primarily by electrostatic effects. The clearest experimental ... | Wikipedia - Pi-stacking - Benzene dimers and related species > Direct interaction model | 332 | 1,725 | null |
Sherill and Sinnokrot reported a surprising finding using high-level theory that all substituted benzene dimers have more favorable binding interactions than a benzene dimer in the sandwich configuration. Later computational work from the Sherill group revealed that the substituent effects for the sandwich configuratio... | Wikipedia - Pi-stacking - Benzene dimers and related species > Direct interaction model | 338 | 1,720 | null |
Section: Requirement of aromaticity. The conventional understanding of pi stacking involves quadrupole interactions between delocalized electrons in p-orbitals. In other words, aromaticity should be required for this interaction to occur. However, several groups have provided contrary evidence, calling into question wh... | Wikipedia - Pi-stacking - Requirement of aromaticity | 328 | 1,656 | null |
Grimme reported that the interaction energies of smaller dimers consisting of one or two rings are very similar for both aromatic and saturated compounds. This finding is of particular relevance to biology, and suggests that the contribution of pi systems to phenomena such as stacked nucleobases may be overestimated. H... | Wikipedia - Pi-stacking - Requirement of aromaticity | 349 | 1,743 | null |
Section: Graphite > π-effects in biological systems. Cation-π interactions are important for the acetylcholine (Ach) neurotransmitter. The structure of acetylcholine esterase includes 14 highly conserved aromatic residues. The trimethyl ammonium group of Ach binds to the aromatic residue of tryptophan (Trp). The indole... | Wikipedia - Pi-stacking - Graphite > π-effects in biological systems | 195 | 825 | null |
Section: Graphite > Supramolecular assembly. π − π {\displaystyle {\ce {\pi - \pi}}} , CH − π {\displaystyle {\ce {CH-\pi}}} and π − cation {\displaystyle {\ce {\pi -cation}}} interactions are widely observed motifs in supramolecular assembly and recognition. π − π {\displaystyle {\ce {\pi-\pi}}} concerns the direct in... | Wikipedia - Pi-stacking - Graphite > Supramolecular assembly | 336 | 1,165 | null |
Section: Reactions. The Hajos–Parrish–Eder–Sauer–Wiechert reaction, reported in 1971 by several research teams, is an early example of an enantioselective catalytic reaction in organic chemistry. Its scope has been modified and expanded through the development of related reactions including the Michael addition, asymme... | Wikipedia - Proline organocatalysis - Reactions | 345 | 1,505 | null |
Section: Mechanistic considerations. Proline-catalyzed aldol additions proceed via a six-membered enamine transition state according to the Zimmerman-Traxler model. Addition of 20-30 mol% proline to acetone or hydroxyacetone catalyzes their addition to a diverse set of aldehydes with high (>99%) enantioselectivity yiel... | Wikipedia - Proline organocatalysis - Mechanistic considerations | 182 | 796 | null |
Article: Push–pull olefin. A push-pull olefin is a type of olefin characterized by an electron-withdrawing substituent on one side of the double bond and an electron-donating substituent on the other side. This makes the pi bond very polarized. The rotational barrier for a push-pull olefin is lower than that of an ordi... | Wikipedia - Push–pull olefin - Summary | 174 | 771 | null |
Section: Synthesis. The formation of chiral quaternary carbon centers has been a synthetic challenge. Chemists have developed asymmetric Diels–Alder reactions, Heck reaction, Enyne cyclization, cycloaddition reactions, C–H activation, Allylic substitution, Pauson–Khand reaction, etc. to construct asymmetric quaternary ... | Wikipedia - Quaternary carbon - Synthesis | 154 | 645 | null |
Section: History. The first known racemic mixture was racemic acid, which Louis Pasteur found to be a mixture of the two enantiomeric isomers of tartaric acid. He manually separated the crystals of a mixture, starting from an aqueous solution of the sodium ammonium salt of racemate tartaric acid. Pasteur benefited from... | Wikipedia - Racemic mixture - History | 153 | 654 | null |
Section: Properties. A racemate is optically inactive (achiral), meaning that such materials do not rotate the polarization of plane-polarized light. Although the two enantiomers rotate plane-polarized light in opposite directions, the rotations cancel each other out because they are present in equal amounts of negativ... | Wikipedia - Racemic mixture - Properties | 221 | 1,032 | null |
Section: Crystallization. There are four ways to crystallize a racemate; three of which H. W. B. Roozeboom had distinguished by 1899: Conglomerate (sometimes racemic conglomerate) If the molecules of the substance have a much greater affinity for the same enantiomer than for the opposite one, a mechanical mixture of en... | Wikipedia - Racemic mixture - Crystallization | 312 | 1,362 | null |
A special case of racemic compounds are kryptoracemic compounds (or kryptoracemates), in which the crystal itself has handedness (is enantiomorphic), despite containing both enantiomorphs in a 1:1 ratio. Pseudoracemate (sometimes racemic solid solution) When there is no big difference in affinity between the same and o... | Wikipedia - Racemic mixture - Crystallization | 315 | 1,262 | null |
Section: Synthesis. Without a chiral influence (for example a chiral catalyst, solvent or starting material), a chemical reaction that makes a chiral product will always yield a racemate. That can make the synthesis of a racemate cheaper and easier than making the pure enantiomer, because it does not require special co... | Wikipedia - Racemic mixture - Synthesis | 211 | 915 | null |
Section: Racemic pharmaceuticals. Some drug molecules are chiral, and the enantiomers have different effects on biological entities. They can be sold as one enantiomer or as a racemic mixture. Examples include thalidomide, ibuprofen, cetirizine and salbutamol. A well known drug that has different effects depending on i... | Wikipedia - Racemic mixture - Racemic pharmaceuticals | 334 | 1,325 | null |
Moving from a racemic drug to a chiral specific drug may be done for a better safety profile or an improved therapeutic index. This process is called chiral switching and the resulting enantiopure drug is called a chiral switch. As examples, esomeprazole is a chiral switch of (±)-omeprazole and levocetirizine is a chir... | Wikipedia - Racemic mixture - Racemic pharmaceuticals | 326 | 1,259 | null |
Article: Radical disproportionation. Radical disproportionation encompasses a group of reactions in organic chemistry in which two radicals react to form two different non-radical products. Radicals in chemistry are defined as reactive atoms or molecules that contain an unpaired electron or electrons in an open shell. ... | Wikipedia - Radical disproportionation - Summary | 181 | 918 | null |
Section: Disproportionation and steric effects. Radical disproportionation is often thought of as occurring in a linear fashion with the donor radical, the acceptor radical, and the atom being accepted all along the same axis. In fact, most disproportionation reactions do not require linear orientations in space. Molec... | Wikipedia - Radical disproportionation - Disproportionation and steric effects | 162 | 739 | null |
Section: Alkyl radical disproportionation. Alkyl radical disproportionation has been studied extensively in scientific literature. During alkyl radical disproportionation, an alkane and an alkene are the end products and the bond order of the products increases by one over the reactants. Thus the reaction is exothermic... | Wikipedia - Radical disproportionation - Alkyl radical disproportionation | 203 | 579 | null |
Section: Competition with recombination. Another reaction that can sometimes occur instead of disproportionation is recombination. During recombination, two radicals form one new non-radical product and one new bond. Similar to disproportionation, the recombination reaction is exothermic and requires little to no activ... | Wikipedia - Radical disproportionation - Competition with recombination | 155 | 653 | null |
Section: Competition with recombination > Kinetic isotope effect on disproportionation and recombination. When the hydrogen atoms in an alkyl radical are displaced with deuterium, disproportionation proceeds at a slightly slower rate whereas the rate of recombination remains the same. Thus disproportionation is weakly ... | Wikipedia - Radical disproportionation - Competition with recombination > Kinetic isotope effect on disproportionation and recombination | 165 | 698 | null |
Section: Reducing disproportionation in living free radical polymerization. Many polymer chemists are concerned with limiting the rate of disproportionation during polymerization. Although disproportionation results in formation of one new double bond which may react with the polymer chain, a saturated hydrocarbon is a... | Wikipedia - Radical disproportionation - Reducing disproportionation in living free radical polymerization | 150 | 762 | null |
Article: Retrosynthetic analysis. Retrosynthetic analysis is a technique for solving problems in the planning of organic syntheses. This is achieved by transforming a target molecule into simpler precursor structures regardless of any potential reactivity/interaction with reagents. Each precursor material is examined u... | Wikipedia - Retrosynthetic analysis - Summary | 305 | 1,639 | null |
Section: Example. Shown below is a retrosynthetic analysis of phenylacetic acid: In planning the synthesis, two synthons are identified. A nucleophilic "-COOH" group, and an electrophilic "PhCH2+" group. Both synthons do not exist as written; synthetic equivalents corresponding to the synthons are reacted to produce th... | Wikipedia - Retrosynthetic analysis - Example | 212 | 792 | null |
Section: Organic chemistry. Generally distinct types of unsaturated organic compounds are recognized. For hydrocarbons: alkene (unsaturated) vs alkane (saturated) alkyne (unsaturated) vs alkane (saturated) arene (unsaturated) vs cycloalkane (saturated) For organic compounds containing heteroatoms (other than C and H), ... | Wikipedia - Saturated and unsaturated compounds - Organic chemistry | 232 | 904 | null |
Article: Schellman loop. Schellman loops (also called Schellman motifs or paperclips) are commonly occurring structural features of proteins and polypeptides. Each has six amino acid residues (labelled residues i to i+5) with two specific inter-mainchain hydrogen bonds (as in lower figure, i) and a characteristic main ... | Wikipedia - Schellman loop - Summary | 347 | 1,351 | null |
Occasional Schellman loops occur with seven instead of six residues. In these, the CO group of residue i is hydrogen-bonded to the NH of residue i+6, and the CO group of residue i+1 is hydrogen-bonded to the NH of residue i+5. Rare “left-handed” six-residue Schellman loops occur; these have the same hydrogen bonds, but... | Wikipedia - Schellman loop - Summary | 329 | 1,366 | null |
Article: Schlenk equilibrium. The Schlenk equilibrium, named after its discoverer Wilhelm Schlenk, is a chemical equilibrium taking place in solutions of Grignard reagents and Hauser bases 2 RMgX ⇌ MgX2 + MgR2 The process described is an equilibrium between two equivalents of an alkyl or aryl magnesium halide on the le... | Wikipedia - Schlenk equilibrium - Summary | 315 | 1,337 | null |
Section: Usage > Biochemistry. In proteins, which are composed of amino acid residues, the side chains are attached to the alpha-carbon atoms of the amide backbone. The side chain connected to the alpha-carbon is specific for each amino acid and is responsible for determining charge and polarity of the amino acid. The ... | Wikipedia - Side chain - Usage > Biochemistry | 168 | 900 | null |
Article: Sigma electron donor-acceptor. The sEDA parameter (sigma electron donor-acceptor) is a sigma-electron substituent effect scale, described also as inductive and electronegativity related effect. There is also a complementary scale - pEDA. The more positive is the value of sEDA the more sigma-electron donating i... | Wikipedia - Sigma electron donor-acceptor - Summary | 342 | 1,402 | null |
Article: Skeletal formula. The skeletal formula, line-angle formula, bond-line formula or shorthand formula of an organic compound is a type of minimalist structural formula representing a molecule's atoms, bonds and some details of its geometry. The lines in a skeletal formula represent bonds between carbon atoms, unl... | Wikipedia - Skeletal formula - Summary | 323 | 1,783 | null |
Section: The skeleton > Terminology. The skeletal structure of an organic compound is the series of atoms bonded together that form the essential structure of the compound. The skeleton can consist of chains, branches and/or rings of bonded atoms. Skeletal atoms other than carbon or hydrogen are called heteroatoms. The... | Wikipedia - Skeletal formula - The skeleton > Terminology | 239 | 1,153 | null |
Section: The skeleton > Basic structure. As in Lewis structures, covalent bonds are indicated by line segments, with a doubled or tripled line segment indicating double or triple bonding, respectively. Likewise, skeletal formulae indicate formal charges associated with each atom, with lone pairs usually being optional ... | Wikipedia - Skeletal formula - The skeleton > Basic structure | 330 | 1,519 | null |
Heteroatoms with simple alkyl or aryl substituents, like methoxy (OMe) or dimethylamino (NMe2), are sometimes shown in the same way, by analogy. Lone pairs on carbene carbons must be indicated explicitly while lone pairs in other cases are optional and are shown only for emphasis. In contrast, formal charges and unpair... | Wikipedia - Skeletal formula - The skeleton > Basic structure | 225 | 1,033 | null |
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