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Thermodynamic Control
Thermodynamic reaction control or kinetic reaction control in a chemical reaction can decide the composition in a reaction product mixture when competing pathways lead to different products and the reaction conditions influence the conversion (chemistry), selectivity or stereoselectivity. The distinction is relevant when product A forms faster than product B because the activation energy for product A is lower than that for product B, yet product B is more stable. In such a case A is the kinetic product and is favoured under kinetic control and B is the thermodynamic product and is favoured under thermodynamic control.Introduction to Organic Chemistry I, Seth Robert Elsheimer, Blackwell Publishing, 2000 The conditions of the reaction, such as temperature, pressure, or solvent, affect which reaction pathway may be favored: either the kinetically controlled or the thermodynamically controlled one. Note this is only true if the activation energy of the two pathways differ, with one ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exo Isomer
Exo (; stylized in all caps) is a South Korean-Chinese boy band based in Seoul formed by SM Entertainment in 2011 and debuted in 2012. The group consists of nine members: Xiumin, Suho, Lay, Baekhyun, Chen, Chanyeol, D.O., Kai and Sehun. They are noted for releasing music and performing extensively in Korean, Mandarin and Japanese. The group debuted with twelve members separated into Exo-K (Suho, Baekhyun, Chanyeol, D.O., Kai and Sehun) and Exo-M (Xiumin, Lay, Chen, Kris, Luhan and Tao). Members Kris, Luhan, and Tao departed the group individually amid legal battles with SM Entertainment in 2014 and 2015. Exo-K and Exo-M performed music in Korean and Mandarin, respectively, until the release of their third EP ''Overdose'' in 2014. Since then, Exo have exclusively performed as one group, although their music continues to feature multiple languages. Members Chen, Baekhyun, and Xiumin debuted in the sub-unit Exo-CBX in 2016. Members Sehun and Chanyeol began promoting as the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protonation
In chemistry, protonation (or hydronation) is the adding of a proton (or hydron, or hydrogen cation), usually denoted by H+, to an atom, molecule, or ion, forming a conjugate acid. (The complementary process, when a proton is removed from a Brønsted–Lowry acid, is deprotonation.) Some examples include * The protonation of water by sulfuric acid: *: H2SO4 + H2O H3O+ + * The protonation of isobutene in the formation of a carbocation: *: (CH3)2C=CH2 + HBF4 (CH3)3C+ + * The protonation of ammonia in the formation of ammonium chloride from ammonia and hydrogen chloride: *: NH3( g) + HCl( g) → NH4Cl( s) Protonation is a fundamental chemical reaction and is a step in many stoichiometric and catalytic processes. Some ions and molecules can undergo more than one protonation and are labeled polybasic, which is true of many biological macromolecules. Protonation and deprotonation (removal of a proton) occur in most acid–base reactions; they are the core of most acid–base r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isomerization
In chemistry, isomerization or isomerisation is the process in which a molecule, polyatomic ion or molecular fragment is transformed into an isomer with a different chemical structure. Enolization is an example of isomerization, as is tautomerization. When the activation energy for the isomerization reaction is sufficiently small, both isomers can often be observed and the equilibrium ratio will shift in a temperature-dependent equilibrium with each other. Many values of the standard free energy difference, \Delta G^\circ, have been calculated, with good agreement between observed and calculated data. Examples and applications Alkanes Skeletal isomerization occurs in the cracking process, used in the petrochemical industry to convert straight chain alkanes to isoparaffins as exemplified in the conversion of normal octane to 2,5-dimethylhexane (an "isoparaffin"): : Fuels containing branched hydrocarbons are favored for internal combustion engines for their higher octan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Activation Energy
In the Arrhenius model of reaction rates, activation energy is the minimum amount of energy that must be available to reactants for a chemical reaction to occur. The activation energy (''E''a) of a reaction is measured in kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol). Activation energy can be thought of as a magnitude of the potential barrier (sometimes called the energy barrier) separating minima of the potential energy surface pertaining to the initial and final thermodynamic state. For a chemical reaction to proceed at a reasonable rate, the temperature of the system should be high enough such that there exists an appreciable number of molecules with translational energy equal to or greater than the activation energy. The term "activation energy" was introduced in 1889 by the Swedish scientist Svante Arrhenius. Other uses Although less commonly used, activation energy also applies to nuclear reactions and various other physical phenomena. Temperature ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transition State Theory
In chemistry, transition state theory (TST) explains the reaction rates of elementary chemical reactions. The theory assumes a special type of chemical equilibrium (quasi-equilibrium) between reactants and activated transition state complexes. TST is used primarily to understand qualitatively how chemical reactions take place. TST has been less successful in its original goal of calculating absolute reaction rate constants because the calculation of absolute reaction rates requires precise knowledge of potential energy surfaces, but it has been successful in calculating the standard enthalpy of activation (Δ''H''‡, also written Δ‡''H''ɵ), the standard entropy of activation (Δ''S''‡ or Δ‡''S''ɵ), and the standard Gibbs energy of activation (Δ''G''‡ or Δ‡''G''ɵ) for a particular reaction if its rate constant has been experimentally determined (the ‡ notation refers to the value of interest ''at the transition state''; Δ''H''‡ is the difference between the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kin Therm Control Diels-alder
Kin usually refers to kinship and family. Kin or KIN may also refer to: Places * Kin empires and dynasties of China, now romanized as ''Jin'' * Kin, Okinawa, a town in Okinawa, Japan * Kin, Pakistan, a village along the Indus in Pakistan * Kin, Ye, a village in Ye Township, Myanmar * Kin, Mogok, a village in Mogok Township, Myanmar Arts, entertainment, and media Music * ''Kin'' (iamamiwhoami album), 2012 * ''KIN'' (KT Tunstall album), 2016 * ''Kin'' (Pat Metheny album), 2014 * ''Kin'' (Mogwai album), 2018 * ''Kin'' (Xentrix album), 1992 * ''Kin'' (Whitechapel album), 2021 Film * ''Kin'', a 2000 South African-British film by Elaine Proctor * ''Kin'' (film), a 2018 American science fiction film *''Kin'', upcoming Australian film written by Thomas Atkin, winner of the 2021 John Hinde Award for Excellence in Science-Fiction Writing Television * "Kin" (''Justified''), a 2013 episode * "Kin" (''The Last of Us''), a 2023 episode * ''Kin'' (Irish TV series), Dubli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemoselectivity
Chemoselectivity is the preferential reaction of a chemical reagent with one of two or more different functional groups. In a chemoselective system, a reagent in the presence of an aldehyde and an ester would mostly target the aldehyde, even if it has the option to react with the ester. Chemoselectivity is an area of interest in chemistry because scientists want to recreate complex biological compounds, such as natural products, and make specific modifications to them. Most chemical reactions bring together atoms that have negative charge character and atoms that have positive charge character. When evaluating possible reaction outcomes, several factors should be considered. The most important being identifying where in the molecule has the most electron density and where has the least. This analysis gives a good prediction of reactivity, but more factors such as connectivity, atomic orbital overlap, solvent effects, and the addition of supporting reagents can affect the reaction o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dimethyl Acetylenedicarboxylate
Ethane ( , ) is a naturally occurring organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petrochemical by-product of petroleum refining. Its chief use is as feedstock for ethylene production. The ethyl group is formally, although rarely practically, derived from ethane. History Ethane was first synthesised in 1834 by Michael Faraday, applying electrolysis of a potassium acetate solution. He mistook the hydrocarbon product of this reaction for methane and did not investigate it further. The process is now called Kolbe electrolysis: : CH3COO− → CH3• + CO2 + e− : CH3• + •CH3 → C2H6 During the period 1847–1849, in an effort to vindicate the radical theory of organic chemistry, Hermann Kolbe and Edward Frankland produced ethane by the reductions of propionitrile ( ethyl cyanide) and ethyl iodi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hexafluoro-2-butyne
Hexafluoro-2-butyne (HFB) is a fluorocarbon with the chemical structure CF3C≡CCF3. HFB is a particularly electrophilic alkyne, acetylene derivative (chemistry), derivative, and hence a potent dienophile for Diels–Alder reactions. Synthesis and reactions HFB is prepared by the action of sulfur tetrafluoride on acetylenedicarboxylic acid or by the reaction of potassium fluoride (KF) with hexachlorobutadiene. In the presence of the strong Lewis acid aluminium chlorofluoride, hexafluorobutadiene isomerizes to HFB: : HFB reacts with sulfur to give 3,4-Bis(trifluoromethyl)-1,2-dithiete, 3,4-bis(trifluoromethyl)-1,2-dithiete. Cycloaddition of HFB and Dithionitronium hexafluoroarsenate, dithionitronium (NS2+) gives the 1,2,5-dithiazolium cation. This derivative can be reduced to the 7 electron neutral radical. This particular 1,3,5-dithiazole is also rare example of a radical that can be obtained as solid, liquid, and gaseous states. As a gas, it is blue. As an electrophilic alk ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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.Tietze, L. F.; Beifuss, U. ''Angew. Chem. Int. Ed.'' 1993, ''32'', 131–163. In cascade reactions, isolation of intermediates is not required, as each reaction composing the sequence occurs spontaneously. In the strictest definition of the term, the reaction conditions do not change among the consecutive steps of a cascade and no new reagents are added after the initial step.Padwa, A.; Bur, S. K. ''Tetrahedron'' 2007, ''63'', 5341–5378. By contrast, one-pot procedures similarly allow at least two reactions to be carried out consecutively without any isolation of intermediates, but do not preclude the addition of new reagents or the change of conditions after the first reaction. Thus, any cascade reaction is also a one-pot p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
