On the flip side, reactions (and excuses) haven't changed too much from Republicans.
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Side reactions in the chemistry increase when you drain the battery to 2% and constantly recharge to 21%.
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Over time, natural side reactions between battery chemicals cause these pipes to clog up, so the water can't flow as quickly and gets stuck.
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Their reactive nature allows them to engage in unnecessary side reactions causing cellular impairment and eventually injury when they are present in disproportionate amounts.
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"By using common materials, but arranging them with nanotechnology, we figured out how to limit the side reactions and end up with the one thing that we want," Rondinone said in a press release.
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Our process runs about 100 degrees centigrade lower in temperature and our productivities, which is kind of how much product can you make per volume of reactor per hour are much higher and our product is also much cleaner, so we don't make side products, for instance, caused by racemisation or other side reactions because we work at a lower temperature.
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Enone–alkene cycloadditions often suffer from side reactions, e.g. those associated with the diradical intermediate. These side reactions can often be minimized by a judicious choice of reaction conditions. Dissolved oxygen is avoided since it is photo reactive.
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Also the state of equilibrium depends on temperature. Detection reactions can be distorted by side reactions.
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Because of side reactions forming thiosulfate (nonregenerable), there is a small makeup requirement in the form of trona (sodium carbonate).
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Substituted chalcones were also synthesised by piperidine-mediated condensation to avoid side reactions such as multiple condensations, polymerizations, and rearrangements.
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Direct anionic polymerization of nitroxyl-containing monomers has also been used to synthesis PTMA. Anionic polymerization is not ideal because it must be carried using very strict procedures to avoid side reactions. Using 1,1-diphenylhexylllithium as an initiator of the reaction eliminates some side reactions by steric effects,Allgaier, J.; Finkelmann, H. Makromol. Chem., Rapid Commun.
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This ensures that the boronic acid concentration is low during the cross-coupling reaction, which in turn minimises the potential for side reactions.
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The limiting step in the first synthesis was the very imprecise reduction with LAH, which proceeded with several side reactions and little reaction specificity. Wallcave et al.
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This reaction is very exothermic. The change of enthalpy of this reaction is equal to -481.06 kJ. The heat provided by the main reaction serves as a catalyst for other side reactions. :CH4 \+ H2O → CO + 3 H2 :2 CH4 \+ 3 O2 → 2 CO + 4 H2O :4 NH3 \+ 3 O2 → 2 N2 \+ 6 H2O These side reactions can be reduced by only short exposures to the catalyst of the order of 0.0003s.
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Hydrogen cyanide alone is not reactive enough to add to carbonyl groups; as a result, base catalysis is necessary. Conjugative hydrocyanation is limited by some side reactions and the strongly basic conditions typically employed. Product hydrolysis should be expected in reactions of alkali metal cyanides. Epimerization at the α-position of carbonyls, double bond isomerization, and α-acetoxy rearrangements have all been observed as side reactions under basic conditions.
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Phenylphosphine can be produced by reducing dichlorophenylphosphine with lithium aluminum hydride in ether: :LiAlH4 \+ 2C6H5PCl2 → 2C6H5PH2 \+ Li+ \+ Al3+ \+ 4Cl− This reaction is performed under a nitrogen atmosphere to prevent side reactions involving oxygen.
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Side reactions are also described in the reaction kinetics, a branch of physical chemistry. Side reactions are understood as complex reaction, since the overall reaction (main reaction + side reaction) is composed of several (at least two) elementary reactions. Other complex reactions are competing reactions, parallel reactions, consecutive reactions, chain reactions, reversible reactions, etc. [10] If one reaction occurs much faster than the other one (k1 > k2), it (k1) will be called the main reaction, the other one (k2) side reaction.
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The anode (zinc) reaction is comparatively simple with a known potential. Side reactions and depletion of the active chemicals increases the internal resistance of the battery, which causes the terminal voltage to drop under load.
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The Wolff–Kishner reduction is not suitable for base–sensitive substrates and can under certain conditions be hampered by steric hindrance surrounding the carbonyl group. Some of the more common side-reactions are listed below.
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In this one-pot system, intermediate purification is unnecessary, so the risk of unwanted products and side reactions are more probable. Matching compatible catalysts would eliminate the likelihood of a catalyst starving or saturating the system, which may cause the catalyst to decompose or generate unwanted side reactions. If side products were to be generated, it may be capable of interfering with the catalytic system. Thus in-depth knowledge is required of the mechanistic characteristics of both catalytic processes and the activity of the catalysts.
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Later work has shown that production of bisphenol A can be made much more selective by using a reaction mixture with a considerable excess of phenol rather than a stoichiometric 2:1 composition, greatly suppressing side reactions.
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An important aspect of the Simmons–Smith reaction that contributes to its wide usage is its ability to be used in the presence of many functional groups. Among others, the haloalkylzinc-mediated reaction is compatible with alkynes, alcohols, ethers, aldehydes, ketones, carboxylic acids and derivatives, carbonates, sulfones, sulfonates, silanes, and stannanes. However, some side reactions are commonly observed. Most side reactions occur due to the Lewis- acidity of the byproduct, ZnI2. In reactions that produce acid-sensitive products, excess Et2Zn can be added to scavenge the ZnI2 that is formed, forming the less acidic EtZnI.
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Metal-catalyzed cyclization reactions usually require mildly basic conditions, and substrates must be chosen to avoid β-hydride elimination. The primary limitation of radical cyclizations with respect to these other methods is the potential for radical side reactions.
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For example, external PCs typically complicate reaction design because the PC may react with both the bound and unbound substrate. If a reaction occurs between the unbound substrate and the PC, enantioselectivity is lost and other side reactions may occur.
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Delepin reaction Advantages of this reaction are selective access to the primary amine without side reactions from easily accessible reactants with short reaction times and relatively mild reaction conditions. An example is the synthesis of 2-bromoallylamine from 2,3-dibromopropene.
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When using oxalyl chloride as the dehydration agent, the reaction must be kept colder than −60 °C to avoid side reactions. With cyanuric chloride or trifluoroacetic anhydride instead of oxalyl chloride, the reaction can be warmed to −30 °C without side reactions. Other methods for the activation of DMSO to initiate the formation of the key intermediate 6 are the use of carbodiimides (Pfitzner–Moffatt oxidation), a sulfur trioxide pyridine complex (Parikh–Doering oxidation) or acetic anhydride (Albright-Goldman oxidation). The intermediate 4 can also be prepared from dimethyl sulfide and N-chlorosuccinimide (the Corey–Kim oxidation).
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The azide group is particularly bioorthogonal because it is extremely small (favorable for cell permeability and avoids perturbations), metabolically stable, and does not naturally exist in cells and thus has no competing biological side reactions. Although azides are not the most reactive 1,3-dipole available for reaction, they are preferred for their relative lack of side reactions and stability in typical synthetic conditions. The alkyne is not as small, but it still has the stability and orthogonality necessary for in vivo labeling. Cyclooctynes are traditionally the most common cycloalkyne for labeling studies, as they are the smallest stable alkyne ring.
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The optimized conditions minimize side reactions, such as the competing Norrish type I pathway, and furnish the desired intermediate in good yield on a multi-gram scale. Type II Norrish reaction in Phil Baran's total synthesis of the biologically active cardenolide ouabagenin.
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This would lead to undesirable side reactions, and thus falsifying a result consumption of bromine. For educational purposes, Simurdiak et al. (2016) suggested the use of pyridinium tribromide as bromination reagent which is more safer in chemistry class and reduces drastically the reaction time.
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A semi-solid cell based on the couple utilizes fluid electrodes that are electronically conductive. Simultaneous advection and electrochemical transport separates flow-induced losses from those due to underlying side reactions. Plug flow is used to achieve energy efficiency with non-Newtonian flow electrodes.
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Radical cyclizations are often reductive, which can cause undesired side reactions to occur if sensitive substrates are employed. The IMHR, on the other hand, can be run under reductive conditions if desired.Burns, B.; Grigg, R.; Ratananukul, P.; Sridharan, V.; Stevenson, P.; Worakun, T. Tetrahedron Lett. 1988, 29, 4329.
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Aquion Energy's batteries are classified as standard goods with no special handling required in shipment. It has no life-reducing side reactions while not in use. It is robust to any variable cycling profiles and long duration intervals while partially charged. Maintenance cycling to maintain performance/life is unnecessary.
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535 The related reaction dealing with aryl halides is called the Wurtz–Fittig reaction. This can be explained by the formation of free radical intermediate and its subsequent disproportionation to give alkene. The Wurtz reaction occurs through a free radical mechanism that makes possible side reactions producing alkene products.
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The most commonly used example are the dithienylethenes, i.e. alkenes with a thiophene ring on either side. Dithienylethene derivatives have shown different types of photochemical side reactions, e.g., oxidation or elimination reactions of the ring-closed isomer and formation of an annulated ring isomer as a byproduct of the photochromic reaction.
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In some indicators, such as phenolphthalein, one of the species is colorless, whereas in other indicators, such as methyl red, both species confer a color. While pH indicators work efficiently at their designated pH range, they are usually destroyed at the extreme ends of the pH scale due to undesired side reactions.
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In particular, the saponins from Quillaja saponaria are used in veterinary vaccines as adjuvant (e.g., foot-and-mouth disease vaccines, helping to enhance the immune response). Initially the crude fraction was used. Later on, a purified mixture called Quil A was developed by Dalsgaard, which was more effective and caused fewer local side reactions.
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Trimethyl phosphate is a mild methylating agent, useful for dimethylation of anilines and related heterocyclic compounds. The method is complementary to the traditional Eschweiler-Clarke reaction in cases where formaldehyde engages in side reactions. Trimethyl phosphate is used as a solvent for aromatic halogenations and nitrations as required for the preparation of pesticides and pharmaceuticals.
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Charcoal may be used as a source of carbon in chemical reactions. One example of this is the production of carbon disulphide through the reaction of sulfur vapors with hot charcoal. In that case the wood should be charred at high temperature to reduce the residual amounts of hydrogen and oxygen that lead to side reactions.
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The haloform reaction can also occur inadvertently in domestic settings. Bleaching with hypochlorite generates halogenated compounds in side reactions; chloroform is the main byproduct. Sodium hypochlorite solution (chlorine bleach) mixed with common household liquids such as acetone, methyl ethyl ketone, ethanol, or isopropyl alcohol can produce some chloroform, in addition to other compounds such as chloroacetone or dichloroacetone.
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For instance, the following side-reactions could lead to byproduct formation: Imine formation steps: 1.Nucleophilic attack of ammonia at the β-, rather than α-carbon will prevent enamine/imine formation 2.Nucleophilic attack of ammonia on the enamine or imine Aldol condensation step 3.(In the case of asymmetric ketones), abstraction of the non-preferred β-Hydrogen 4.
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These interactions decrease the activation energy of a chemical reaction by providing favorable interactions to stabilize the high energy molecule. Enzyme binding allows for closer proximity and exclusion of substances irrelevant to the reaction. Side reactions are also discouraged by this specific binding. Types of enzymes that can perform these actions include oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.
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Procedures to prevent side reactions include the inverse addition of the enolate to MoOPH or careful control of the temperature (-78 to -20 °C). Notable miscellaneous reactions include MoOPH’s ability to oxidize alkylboranes directly to the alcohol with net stereo-retention. MoOPH has also been shown to oxidize N-trimethylsilyl amides directly to the hydroxamic acid.
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In comparison to cationic cyclizations, radical cyclizations avoid issues associated with Wagner-Meerwein rearrangements, do not require strongly acidic conditions, and can be kinetically controlled. Cationic cyclizations are usually thermodynamically controlled. Radical cyclizations are much faster than analogous anionic cyclizations, and avoid β-elimination side reactions. Anionic Michael-type cyclization is an alternative to radical cyclization of activated olefins.
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Even though residence time and temperature are carefully controlled, it produces significant quantities of chlorinated hydrocarbon side products. In practice, the yield for EDC conversion is relatively low (50 to 60 percent). The furnace effluent is immediately quenched with cold EDC to stop undesirable side reactions. The resulting vapor-liquid mixture then goes to a purification system.
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In organic synthesis, SF4 is used to convert COH and C=O groups into CF and CF2 groups, respectively. Certain alcohols readily give the corresponding fluorocarbon. Ketones and aldehydes give geminal difluorides. The presence of protons alpha to the carbonyl leads to side reactions and diminished (30–40%) yield. Also diols can give cyclic sulfite esters, (RO)2SO.
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Faradaic losses are experienced by both electrolytic and galvanic cells when electrons or ions participate in unwanted side reactions. These losses appear as heat and/or chemical byproducts. An example can be found in the oxidation of water to oxygen at the positive electrode in electrolysis. Some electrons are diverted to the production of hydrogen peroxide.
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This hinders the use of the MPV reduction on scale. Recent work has shown that aluminium alkoxides made in situ from trimethyl aluminium reagents have far better activity requiring as little as 10% loading. The activity difference is believed to be due to the large aggregation state of the commercially available product. Several side reactions are known to occur.
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The LTS shift reactor operates at a range of 200–250 °C. The upper temperature limit is due to the susceptibility of copper to thermal sintering. These lower temperatures also reduce the occurrence of side reactions that are observed in the case of the HTS. Noble metals such as platinum, supported on ceria, have also been used for LTS.
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If an α-halo ketone is used, the product is an α,β-epoxy ketone. Any sufficiently strong base can be used for the initial deprotonation. However, if the starting material is an ester, the alkoxide corresponding to the ester side-chain is commonly chosen in order to prevent complications due to potential acyl exchange side reactions.
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Battery life can be extended by storing the batteries at a low temperature, as in a refrigerator or freezer, which slows the side reactions. Such storage can extend the life of alkaline batteries by about 5%; rechargeable batteries can hold their charge much longer, depending upon type.Ask Yahoo: Does putting batteries in the freezer make them last longer? . Retrieved 7 March 2007.
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Conducting polymer coatings, an organic electronic material, shows massive improvement in the technology of materials. It was the most sophisticated form of electrical stimulation. It improved the impedance of electrodes in electrical stimulation, resulting in better recordings and reducing "harmful electrochemical side reactions." Organic Electrochemical Transistors (OECT) were invented in 1984 by Mark Wrighton and colleagues, which had the ability to transport ions.
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A second carbenium species is produced by protonation and loss of the aliphatic hydroxyl group, leading to bisphenol A (4,4'-isopropylidenediphenol) after a second aromatic substitution reaction. The process is not very selective, and a great number of minor products and side reactions are known. Structure of Dianin's compound, a chroman side-product of Dianin's synthesis of bisphenol A. Side products that are isomers of bisphenol A result from the formation of ortho- substituted products, and include the 2,2'- and 2,4'- isomers of isopropylidenediphenol. Other side reactions include the formation of triphenol I, 4,4'-(4-hydroxy-m-phenylenediisopropylidene)diphenol, from the attack of a carbenium electrophile on a bisphenol A molecule and the formation of triphenol II, 4,4',4-(2-methyl-2-pentanyl-4-ylidene)triphenol, when an elimination reaction converts the carbenium to a reactive olefin.
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Not only are there fewer nitroxide groups present, but also side reactions between non-oxidized groups and oxammonium cations diminishes the redox reversibility of the compound. The difficulties of free-radical polymerization of PTMA could be avoided if the oxidation step were not necessary. However, because nitroxide radicals would react with any carbon radicals formed during polymerization, use of a monomer with a nitroxide radical isn’t practical.
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Formerly, the zinc anodes of dry cells were amalgamated with mercury, to prevent side-reactions of the zinc with the electrolyte that would reduce the service life of the battery. The mercury took no part in the chemical reaction for the battery. Manufacturers have changed to a purer grade of zinc, so amalgamation is no longer required and mercury is eliminated from the dry cell.
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Byproducts can compete with other reagents for benzyne trapping, cause side-reactions, and may require additional purification. Additionally, the HDDA reaction can be useful for substrates with sensitive functionality that might not be tolerated by other benzyne formation conditions (e.g. strong base). The thermally-initiated HDDA reaction has been shown to tolerate esters, ketones, protected amides, ethers, protected amines, aryl halides, alkyl halides, alkenes, and cyclopropanes.
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Several problems restrict the use of the Meerwein–Ponndorf–Verley reduction compared to the use of other reducing agents. The stereochemical control is seriously limited. Often a large amount of aluminium alkoxide is needed when using commercial reagent, and there are several known side reactions. While commercial aluminium isopropoxide is available, the use of it often requires catalyst loadings of up to 100-200 mol%.
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The HOCl byproduct, itself a reactive oxidizing agent, can be a problem in several ways. It can destroy the NaClO2 reactant: :HOCl + 2ClO2− → 2ClO2 \+ Cl− \+ OH− making it unavailable for the desired reaction. It can also cause other undesired side reactions with the organic materials. For example, HOCl can react with double bonds in the organic reactant or product via a halohydrin formation reaction.
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The reaction mechanism is not yet clear in details, as several side reactions are taking place. Expanding monomers can not just be homopolymerized as it is shown here but also copolymerized with other monomers to counteract their shrinking. Usually a Lewis acid like boron trifluoride etherate is used for both, the synthesis of the orthoester and the polymerization. The same applies for spiro orthocarbonates and bicyclic orthoesters.
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This pre-organization also serves purposes such as minimizing side reactions, lowering the activation energy of the reaction, and producing desired stereochemistry. After the reaction has taken place, the template may remain in place, be forcibly removed, or may be "automatically" decomplexed on account of the different recognition properties of the reaction product. The template may be as simple as a single metal ion or may be extremely complex.
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2011.222 Polymerization reactions of the stable radical-containing monomer have also proved to be an area of difficulty in development. The stable organic radicals that are crucial to the functioning of the battery are sometimes consumed in side-reactions of various polymerization reactions. A research group has, however, successfully synthesized a cross-linked organic radical polymer while only losing 0.4% of the organic radicals in synthesis of the polymer.
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Further, when batteries are recharged, additional side reactions can occur, reducing capacity for subsequent discharges. After enough recharges, in essence all capacity is lost and the battery stops producing power. Internal energy losses and limitations on the rate that ions pass through the electrolyte cause battery efficiency to vary. Above a minimum threshold, discharging at a low rate delivers more of the battery's capacity than at a higher rate.
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The disadvantages of the reaction involve side reactions of the carbene moiety. The choice of solvent for the reaction needs to be considered. In addition to the potential for carbon-hydrogen bond insertion reactions, carbon-halogen carbene insertion is possible when dichloromethane is used as the solvent. C-Cl bond insertion Control for regioselectivity during the carbene addition is necessary to avoid side products resulting from conjugated cycloheptatriene isomers.
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High charging rates may produce excess gas in a battery, or may result in damaging side reactions that permanently lower the battery capacity. Very roughly, and with many exceptions and details, restoring a battery's full capacity in one hour or less is considered fast charging. A battery charger system will include more complex control-circuit- and charging strategies for fast charging, than for a charger designed for slower recharging.
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Other important side reactions include elimination of the alkyl cyanide product or alkyl halide starting material and amidine formation. The cyclization of ω-epoxy-1-nitriles provides an interesting example of how stereoelectronic factors may override steric factors in intramolecular substitution reactions. In the cyclization of 1, for instance, only the cyclopropane isomer 2 is observed. This is attributed to better orbital overlap in the SN2 transition state for cyclization.
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In contrast, when DXP and an HAP analog are bound, loop 4 of the protein folds over the active site, preventing the escape of reaction intermediates or undesirable side reactions. Binding of phosphate alone is not capable of causing a transition between the open and closed states. A third, "partially open" intermediate has also been reported upon binding of DXP alone. pdxJ assembles as an octamer under biological conditions.
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The sodium forms an amalgam with the Hg cathode preventing side reactions and the hydrogen produced in the first reaction could be captured and reacted back with the sodium mercury amalgam to produce sodium hydride. Clasen's system results in no loss of starting material. For insoluble anodes, reaction 1 occurs, while for soluble anodes, anodic dissolution is expected according to reaction 2: 1\. AlH4− \- e− → AlH3 · nTHF + ½H2 2\.
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Two common side reactions are elimination reactions and carbocation rearrangement. If the reaction is performed under warm or hot conditions (which favor an increase in entropy), E1 elimination is likely to predominate, leading to formation of an alkene. At lower temperatures, SN1 and E1 reactions are competitive reactions and it becomes difficult to favor one over the other. Even if the reaction is performed cold, some alkene may be formed.
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In addition to their native reaction, many enzymes perform side reactions. Similarly, binding proteins may spend some proportion of their time bound to off-target proteins. These reactions or interactions may be of no consequence to current fitness but under altered conditions, may provide the starting point for adaptive evolution. For example, several mutations in the antibiotic resistance gene B-lactamase introduce cefotaxime resistance but do not affect ampicillin resistance.
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Conversely, the iron used in the HTS reaction is generally more robust and resistant toward poisoning by sulfur compounds. While both the HTS and LTS catalysts are commercially available, their specific composition varies based on vendor. An important limitation for the HTS is the H2O/CO ratio where low ratios may lead to side reactions such as the formation of metallic iron, methanation, carbon deposition, and the Fischer–Tropsch reaction.
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NBS will react with alkenes 1 in aqueous solvents to give bromohydrins 2. The preferred conditions are the portionwise addition of NBS to a solution of the alkene in 50% aqueous DMSO, DME, THF, or tert-butanol at 0 °C. Formation of a bromonium ion and immediate attack by water gives strong Markovnikov addition and anti stereochemical selectivities. :Bromohydrin formation Side reactions include the formation of α-bromoketones and dibromo compounds.
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In organic synthesis, CAN is useful as an oxidant for many functional groups (alcohols, phenols, and ethers) as well as C–H bonds, especially those that are benzylic. Alkenes undergo dinitroxylation, although the outcome is solvent-dependent. Quinones are produced from catechols and hydroquinones and even nitroalkanes are oxidized. CAN provides an alternative to the Nef reaction; for example, for ketomacrolide synthesis where complicating side reactions usually encountered using other reagents.
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An advantage of the step-polymerization approach is that ortho-, meta-, and para-xylylene linkages can be incorporated in the main chain. Copolymers of defined stereoregularity can also be easily made in this way. PPV derivatives can be also produced via the Knoevenagel condensation between a benzylic nitrile and an aromatic dialdehyde. Since this method produces many side reactions, such as hydrolysis of nitrile group, careful optimization of the reaction conditions was needed.
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Peptides are chemically synthesized by the condensation reaction of the carboxyl group of one amino acid to the amino group of another. Protecting group strategies are usually necessary to prevent undesirable side reactions with the various amino acid side chains. Chemical peptide synthesis most commonly starts at the carboxyl end of the peptide (C-terminus), and proceeds toward the amino- terminus (N-terminus). Protein biosynthesis (long peptides) in living organisms occurs in the opposite direction.
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Although the substrate scope of PLE is broad, enantioselectivity varies as a function of the structure of the substrate. This section describes substrates that are hydrolyzed by PLE with the highest enantioselectivity, as well as sensitive substrates that may be hydrolyzed to achiral carboxylic acids in high yield without side reactions. Glutarates were the first substrates to be hydrolyzed with PLE in high enantioselectivity. Although yields are moderate, enantioselectivity is extremely high.
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Hydrochloric acid generated during the selanylation of transient enol catalyzes tautomerization. (8)File:SelenScope5.png The seleno-Pummerer reaction is a significant side reaction that may occur under conditions when acid is present. Protonation of the selenoxide intermediate, followed by elimination of hydroxide and hydrolysis, leads to α-dicarbonyl compounds. The reaction is not a problem for more electron-rich carbonyls—generally, fewer side reactions are observed in eliminations of esters and amides. (9)File:SelenScope6.
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If a molecule with a low ionization potential (e.g. phenols, polyaromatics) is present in the system, the diffusion-limited electron transfer reaction forms a spin-correlated triplet electron transfer state – a radical pair. The kinetics are complicated and may involve multiple protonations and deprotonations, and hence exhibit pH dependence. An example of Radical Pair Mechanism The radical pair may either cross over to a singlet electron state and then recombine, or separate and perish in side reactions.
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Henbest extended Cram’s procedure by refluxing carbonyl hydrazones and potassium tert-butoxide in dry toluene. Slow addition of the hydrazone is not necessary and it was found that this procedure is better suited for carbonyl compounds prone to base-induced side reactions than Cram's modification. It has for example been found that double bond migration in α,β-unsaturated enones and functional group elimination of certain α-substituted ketones are less likely to occur under Henbest's conditions.
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In these reactions, ladderanes are formed from multiple [2 + 2] photocycloaddiitions between the double bonds of two polyenes. A complication that arises from this approach is the reaction of the precursors through alternative, more favorable photoexcitation routes. These side reactions are prevented by the addition of a chemical spacer unit that holds the two polyenes parallel to each other, only allowing [2 + 2] cycloadditions to occur. A common spacer used in these reactions is the [2.2]paracyclophane system.
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Important side reactions include heterolytic cleavage, in which the homoallylic alcohol decomposes into a carbonyl and an allylic system. 442x442px Suppression of this phenomenon is readily achievable by decreasing the ionic nature of the metal-alkoxide bond. Specifically, the use of more electronegative alkali metals or solvents less amenable to cation solvation generates the desired effect. In keeping with the above discussion, the rate of reaction may be diminished but should not approach an unsatisfactory level.
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In an ideal chemical process, the amount of starting materials or reactants equals the amount of all products generated and no atom is lost. However, in most processes, some of the consumed reactant atoms do not become part of the products, but remain as unreacted reactants, or are lost in some side reactions. Besides, solvents and energy used for the reaction are ignored in this calculation, but they may have non-negligible impacts to the environment.
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The occurrence of side reactions sets practical limits for the length of synthetic oligonucleotides (up to about 200 nucleotide residues) because the number of errors accumulates with the length of the oligonucleotide being synthesized. Products are often isolated by high-performance liquid chromatography (HPLC) to obtain the desired oligonucleotides in high purity. Typically, synthetic oligonucleotides are single-stranded DNA or RNA molecules around 15–25 bases in length. Oligonucleotides find a variety of applications in molecular biology and medicine.
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Anabolism is powered by catabolism, where large molecules are broken down into smaller parts and then used up in cellular respiration. Many anabolic processes are powered by the cleavage of adenosine triphosphate (ATP). Anabolism usually involves reduction and decreases entropy, making it unfavorable without energy input. The starting materials, called the precursor molecules, are joined together using the chemical energy made available from hydrolyzing ATP, reducing the cofactors NAD+, NADP+, and FAD, or performing other favorable side reactions.
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In the effluent treating Section the free acid, alkyl sulfates and di-alkyl sulfates are removed from the net effluent stream to avoid downstream corrosion and fouling using a settler. The sulfuric acid present in the reaction zone serves as a catalyst to the alkylation reaction. Theoretically, a catalyst promotes a chemical reaction without being changed as a result of that reaction. In reality, however, the acid is diluted as a result of the side reactions and feed contaminants.
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Borane dimethylsulfide (BMS) is a complexed borane reagent that is used for hydroborations and reductions. The advantages of BMS over other borane reagents, such as borane-tetrahydrofuran, are its increased stability and higher solubility. BMS is commercially available at much higher concentrations than its tetrahydrofuran counterpart (10 M neat) and does not require sodium borohydride as a stabilizer, which could result in undesired side reactions. In contrast, borane·THF requires sodium borohydride to inhibit reduction of THF to tributyl borate.
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The DuPont evaluations of the 1950s era indicated that polyamide-1,6 was less acid stable than nylon 66, and melts over 300–325 °C, with some decomposition. However, films were reported to have been successfully pressed at 275–290 °C. Molecular weight determined to be ~22,000–34,000 via an osmotic pressure method. The polymer was believed to be significantly branched and cross-linked owing to side reactions occurring during the acid catalyzed polymerization, but this was not conclusively established.
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The formation of amide is promoted by CDI. Although the reactivity of CDI is less than acid chlorides, it is more easily handled and avoids the use of thionyl chloride in acid chloride formation, which can cause side reactions. An early application of this type of reaction was noted in the formation of peptide bonds (with CO2 formation as a driving force). The proposed mechanism for the reaction between a carboxylic acid and CDI is presented below.
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The neutral superbase P4-t-Bu is superior to ionic bases if those are sensitive to oxidation or side reactions (such as acylation) when they cause solubility problems or Lewis acid catalysed side reactions (such as aldol reactions, epoxy ring opening etc). The dehydrohalogenation of n-alkyl bromides yields the alkene, such as the reaction 1-bromooctane with P4-t-Bu which yields 1-octene almost quantitatively (96%) under mild conditions, compared to the potassium tert-butoxide/18-crown-6 system with only 75% yield. Alkylations on weakly acidic methylene groups (e.g. in the case of carboxylic esters or nitriles) proceed with high yield and selectivity. For example, by the reaction of 8-phenylmenthylphenylacetate with iodoethane in the presence of P4-t-Bu only the monoethyl derivative in the Z configuration is obtained in 95% yield. : Monoethylierung von 8-Phenylmenthyl-phenylacetat Succinonitrile reacts with iodoethane in the presence of P4-t-Bu in 98% yield to give the tetraethyl derivative without undergoing a Thorpe-Ziegler reaction to form a cyclic α-ketonitrile.
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The aromatic ring of phenol is activated towards electrophilic substitution reactions, and attempted nitration of phenol, even with dilute nitric acid, results in the formation of high molecular weight tars. In order to minimize these side reactions, anhydrous phenol is sulfonated with fuming sulfuric acid, and the resulting p-hydroxyphenylsulfonic acid is then nitrated with concentrated nitric acid. During this reaction, nitro groups are introduced, and the sulfonic acid group is displaced. The reaction is highly exothermic, and careful temperature control is required.
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The Dubna team repeated their investigation of the 240Pu+48Ca reaction in 2017, observing three new consistent decay chains of 285Fl, an additional decay chain from this nuclide that may pass through some isomeric states in its daughters, a chain that could be assigned to 287Fl (likely stemming from 242Pu impurities in the target), and some spontaneous fission events of which some could be from 284Fl, though other interpretations including side reactions involving the evaporation of charged particles are also possible.
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The Wurtz-Fittig Reaction has limited applicability since side reactions such as rearrangements and eliminations are prevalent. However, the reaction is useful for the laboratory synthesis of organosilicon compounds, although there are challenges in adapting the procedure to a large-scale industrial process. Organosilicon compounds successfully synthesized via the Wurtz-Fittig reaction include silylated calixarenes, t-Butylsilicon compounds, and vinylsilanes. For example, t-butyltriethoxysilane can be prepared via the Wurtz-Fitting reaction by combining tetraoxysilane, t-butyl chloride and molten sodium.
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The major problem associated with alkylation reactions employing nitrile anions is over-alkylation. In the alkylation of acetonitrile, for instance, yields of monoalkylated product are low in most cases. Two exceptions are alkylations with epoxides (the nearby negative charge of the opened epoxide wards off further alkylation) and alkylations with cyanomethylcopper(I) species. Side reactions may also present a problem; concentrations of the nitrile anion must be high to mitigate processes involving self-condensation, such as the Thorpe-Ziegler reaction.
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This enzyme is also part of a larger multienzyme complex that channels the intermediates in the catalysis between subunits of the complex thus minimizing unwanted side reactions. Not only do the subunits ferry products back and forth, but each of the subunits in the E1o homodimer are connected via a cavity lined with acidic residues, thus increasing the dimer's ability to act as a base. The orientation of the cavity allows for direct transfer of the intermediate to the E2o subunit.
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An E1 elimination occurs when a proton adjacent to a positive charge leaves and generates a double bond. 450px Because initial formation of a cation is necessary for E1 reactions to occur, E1 reactions are often observed as side reactions to SN1 mechanisms. 500px E1 eliminations proceed with the Elimination of a leaving group leading to the E designation. Because this mechanism proceeds with the initial dissociation of a single starting material forming a carbocation, this process is considered a uni-molecular reaction.
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The primary difficulty for alkylation reactions employing nitrile anions is over-alkylation. In the alkylation of acetonitrile, for instance, yields of monoalkylated product are low in most cases. Two exceptions are alkylations with epoxides (the nearby negative charge of the opened epoxide wards off further alkylation) and alkylations with cyanomethylcopper(I) species. Side reactions may also present a problem; concentrations of the nitrile anion must be high in order to mitigate processes involving self-condensation, such as the Thorpe–Ziegler reaction.
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Metallic nanoparticles may be beneficial for some technical applications due to their higher magnetic moment whereas oxides (maghemite, magnetite) would be beneficial for biomedical applications. This also implies that for the same moment, metallic nanoparticles can be made smaller than their oxide counterparts. On the other hand, metallic nanoparticles have the great disadvantage of being pyrophoric and reactive to oxidizing agents to various degrees. This makes their handling difficult and enables unwanted side reactions which makes them less appropriate for biomedical applications.
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Although enzymes are generally specific towards their substrate, enzymatic side activities (enzyme promiscuity) can lead to toxic or useless products. These side reactions proceed at much lower rates than their normal physiological reactions, but build-up of damaged metabolites can still be significant over time. For example, the mitochondrial malate dehydrogenase reduces alpha-ketoglutarate to L-2-hydroxyglutarate 107 times less efficiently than its regular substrate oxaloacetate, but L-2-hydroxyglutarate can still accumulate to several grams per day in a human adult.
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Nanoscale particles are below the critical flaw size within a conductive binder film. Reducing transport lengths(the distance between the anode and cathode) reduces ohmic losses (resistance). Nanostructuring increases the surface area to volume ratio, which improves both energy and power density due to an increase in the electrochemically active area and a reduction in transport lengths. However, the increase also increases side reactions between the electrode and the electrolyte, causing higher self-discharge, reduced charge/discharge cycles and lower calendar life.
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In addition, adding electron density to the catalyst (for instance by replacing acetate ligands with acetamide, acam) increases the diastereoselectivity of the reaction.Doyle, M.; Bagheri, V.; Wandless, T.; Harn, N. K.; Brinker, D. A.; Eagle, C.; Loh, K. J. Am. Chem. Soc. 1990, 112, 1906. (5)File:IntraCPScope1.png Diazocarbonyl compounds substituted with two electron-withdrawing groups, such as diazomalonates, are prone to experience side reactions under cyclopropanation conditions. [3+2] CycloadditionPirrung, M. C.; Zhang, J.; Lackey, K.; Sternbach, D. D.; Brown, F. J. Org. Chem.
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Enzyme promiscuity is the ability of an enzyme to catalyse a fortuitous side reaction in addition to its main reaction. Although enzymes are remarkably specific catalysts, they can often perform side reactions in addition to their main, native catalytic activity. These promiscuous activities are usually slow relative to the main activity and are under neutral selection. Despite ordinarily being physiologically irrelevant, under new selective pressures these activities may confer a fitness benefit therefore prompting the evolution of the formerly promiscuous activity to become the new main activity.
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By firing particle beams at targets, many fusion reactions have been tested, while the fuels considered for power have all been light elements like the isotopes of hydrogen—protium, deuterium, and tritium. The deuterium and helium-3 reaction requires helium-3, an isotope of helium so scarce on Earth that it would have to be mined extraterrestrially or produced by other nuclear reactions. Finally, researchers hope to perform the protium and boron-11 reaction, because it does not directly produce neutrons, though side reactions can.
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In photochromic materials, fatigue refers to the loss of reversibility by processes such as photodegradation, photobleaching, photooxidation, and other side reactions. All photochromics suffer fatigue to some extent, and its rate is strongly dependent on the activating light and the conditions of the sample. Photochromic materials have two states, and their interconversion can be controlled using different wavelengths of light. Excitation with any given wavelength of light will result in a mixture of the two states at a particular ratio, called the photostationary state.
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2D nanomaterials also have a few challenges. There are some side effects of modifying the properties of the materials, such as activity and structural stability, which can be compromised when they are engineered. For example, creating some defects can increase the number of active sites for higher catalytic performance, but side reactions may also happen, which could possibly damage the catalyst's structure. Another example is that interlayer expansion can lower the ion diffusion barrier in the catalytic reaction, but it can also potentially lower its structural stability.
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Subsequently, the crude product is separated by distillation into the desired fractions, the fraction preferred for ASA production is the C14 – C22. Isomerisierung von terminalen Alkenen zu iso-Alkenen The alkenyl succinic anhydrides are prepared with an excess of isoalkene at temperatures >200 °C under nitrogen atmosphere for more than 3 hours; the excess iso-alkene is distilled off at reduced pressure. Synthese von ASA mit Maleinsäureanhydrid und iso-Alken Extensive patent literature exists with regard to the suppression of side reactions in the production of ASA.
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The crystals then grow larger, and because the larger crystals have a large volume compared to their surface area it becomes difficult to remove them chemically during charging, particularly as the concentration of the sulfuric acid in the electrolyte is likely to be high (since only limited lead sulfate has been created on the surface of the plate) and lead sulfate is less soluble in concentrated sulfuric acid (above about 10% concentration by weight) than it is in dilute sulfuric acid. This condition is sometimes termed the “hard” sulfation of the battery electrode [REF]. Hard sulfation increases the battery's impedance (since the lead sulfate crystals tend to insulate the electrode from the electrolyte) and decreases its power, capacity and efficiency due to increased undesirable side reactions, some of which occur inside the negative plate due to charging taking place with low availability of lead sulfate (inside the plate body). One undesirable effect is the production of hydrogen inside the plate, further reducing the efficiency of the reaction. “Hard” sulfation is generally irreversible since the side reactions tend to dominate as more and more energy is pushed into the battery.
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Enamines act as nucleophiles that require less acid/base activation for reactivity than their enolate counterparts. They have also been shown to offer a greater selectivity with less side reactions. There is a gradient of reactivity among different enamine types, with a greater reactivity offered by ketone enamines than their aldehyde counterparts. Cyclic ketone enamines follow a reactivity trend where the five membered ring is the most reactive due to its maximally planar conformation at the nitrogen, following the trend 5>8>6>7 (the seven membered ring being the least reactive).
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Organolithium reagents can serve as nucleophiles and carry out SN2 type reactions with alkyl or allylic halides. Although they are considered more reactive than Grignards reactions in alkylation, their use is still limited due to competing side reactions such as radical reactions or metal-halogen exchange. Most organolithium reagents used in a alkylations are more stabilized, less basic, and less aggregated, such as heteroatom stabilized, aryl- or allyllithium reagents. HMPA has been shown to increase reaction rate and product yields, and the reactivity of aryllithium reagents is often enhanced by the addition of potassium alkoxides.
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Secondary alkylating agents also react, but tertiary ones are usually too prone to side reactions to be of practical use. The leaving group is most often a halide or a sulfonate ester synthesized for the purpose of the reaction. Since the conditions of the reaction are rather forcing, protecting groups are often used to pacify other parts of the reacting molecules (e.g. other alcohols, amines, etc.) The Williamson ether synthesis is a common reaction in the field of Organic Chemistry in industrial synthesis and in undergraduate teaching laboratories.
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In 2007, a research group claimed the first reproducible synthesis of unsubstituted hexacene—purportedly invalidating previous claims—based on photochemical decarbonylation of a diketone precursor: :Neckers hexacene synthesis (2007). The compound synthesized could not be isolated: it dimerized at concentrations as low as 10−4 M, and reacted with oxygen in solution to form an organic peroxide. In a poly(methyl methacrylate) polymer matrix such side-reactions were limited, and the compound survived up to 12 hours. The next homologue heptacene also studied by this group, and was even more unstable, decomposing within 4 hours.
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TEMPO oxidations also exhibit chemoselectivity, being inert towards secondary alcohols, but the reagent will convert aldehydes to carboxylic acids. In cases where secondary oxidizing agents cause side reactions, it is possible to stoichiometrically convert TEMPO to the oxoammonium salt in a separate step. For example, in the oxidation of geraniol to geranial, 4-acetamido-TEMPO is first oxidized to the oxoammonium tetrafluoroborate. TEMPO can also be employed in nitroxide-mediated radical polymerization (NMP), a controlled free radical polymerization technique that allows better control over the final molecular weight distribution.
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As long as the nucleophilicity of the alkyl group does not lead to side reactions, catalytic amounts of Lewis acid are sufficient for many ene reactions with reactive enophiles. Nonetheless, the amount of Lewis acid can widely vary, as it largely depends on the relative basicity of the enophile and the ene adduct. In terms of solvent choice for the reactions, the highest rates are usually achieved using halocarbons as solvents; polar solvents such as ethers are not suitable, as they would complex to the Lewis acid, rendering the catalyst inactive.
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Difluoro and monofluoro alcohols are more difficult to oxidize. Swern oxidation has been used, but a large excess of the oxidant had to be employed, and in some cases did not give reproducible results. Linderman and Graves found DMP was successful in most cases but could not tolerate the presence of nucleophilic functional groups in the alcohol, as these reacted with DMP by displacing acetate. Using the compound shown below produced the desired carbonyls in high yields as the addition of the tert-butoxy group, due to its steric bulk, minimizes these side reactions.
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In making peptide segments for use in native chemical ligation, protecting groups that release aldehydes or ketones should be avoided since these may cap the N-terminal cysteine. For the same reason, the use of acetone should be avoided, particularly prior to lyophilization and in washing glassware. A feature of the native chemical ligation technique is that the product polypeptide chain contains cysteine at the site of ligation. For some proteins, homocysteine can be used and methylated after ligation to form methionine, although side reactions can occur in this alkylation step.
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The rate of side reactions is reduced for batteries stored at lower temperatures, although some can be damaged by freezing. Old rechargeable batteries self-discharge more rapidly than disposable alkaline batteries, especially nickel-based batteries; a freshly charged nickel cadmium (NiCd) battery loses 10% of its charge in the first 24 hours, and thereafter discharges at a rate of about 10% a month. However, newer low self-discharge nickel metal hydride (NiMH) batteries and modern lithium designs display a lower self-discharge rate (but still higher than for primary batteries).
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Oligonucleotides are chemically synthesized using building blocks, protected phosphoramidites of natural or chemically modified nucleosides or, to a lesser extent, of non-nucleosidic compounds. The oligonucleotide chain assembly proceeds in the 3' to 5' direction by following a routine procedure referred to as a "synthetic cycle". Completion of a single synthetic cycle results in the addition of one nucleotide residue to the growing chain. A less than 100% yield of each synthetic step and the occurrence of side reactions set practical limits of the efficiency of the process.
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On the other hand, chloromethane and bromomethane are gaseous, thus harder to handle, and are also weaker alkylating agents. Iodide can act as a catalyst when reacting chloromethane or bromomethane with a nucleophile while iodomethane is formed in situ. Iodides are generally expensive relative to the more common chlorides and bromides, though iodomethane is reasonably affordable; on a commercial scale, the more toxic dimethyl sulfate is preferred, since it is cheap and has a higher boiling point. The iodide leaving group in iodomethane may cause unwanted side reactions.
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A DC electrical power source is connected to two electrodes, or two plates (typically made from some inert metal such as platinum or iridium) which are placed in the water. Hydrogen will appear at the cathode (where electrons enter the water), and oxygen will appear at the anode. Assuming ideal faradaic efficiency, the amount of hydrogen generated is twice the amount of oxygen, and both are proportional to the total electrical charge conducted by the solution. However, in many cells competing side reactions occur, resulting in different products and less than ideal faradaic efficiency.
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Explosives with an oxygen deficit will generate soot or gases like carbon monoxide and hydrogen, which may react with surrounding materials such as atmospheric oxygen. Attempts to obtain more precise volume estimates must consider the possibility of such side reactions, condensation of steam, and aqueous solubility of gases like carbon dioxide. By comparison, CDP detonation is based on the rapid reduction of carbon dioxide to carbon with the abundant release of energy. Rather than produce typical waste gases like carbon dioxide, carbon monoxide, nitrogen and nitric oxides, CDP is different.
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Early transition metals can easily form oxides; therefore, protection groups, like the use of methylaluminoxane (MAO) due to its Lewis acidity, can be used to prevent side reactions from happening. As a cocatalyst, MAO is well known for their use in metallocene chemistry as they activate metallocene complexes for olefin polymerization. To remove the MAO protecting group, the reaction can be treated with acid. Instead of MAO, trimethylsilyl (TMS) have also been used to protection functional groups such as amine, since the amine functionality can easily react with other olefins to form branched polymer chains.
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To properly control the polymer molecular weight, the stoichiometric imbalance of the bifunctional monomer or the monofunctional monomer must be precisely adjusted. If the nonstoichiometric imbalance is too large, the polymer molecular weight will be too low. It is important to understand the quantitative effect of the stoichiometric imbalance of reactants on the molecular weight. Also, this is necessary in order to know the quantitative effect of any reactive impurities that may be present in the reaction mixture either initially or that are formed by undesirable side reactions.
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When methionine is followed by serine or threonine, side reactions can occur that destroy the methionine without peptide bond cleavage. Normally, once the iminolactone is formed (refer to figure), water and acid can react with the imine to cleave the peptide bond, forming a homoserine lactone and new C-terminal peptide. However, if the adjacent amino acid to methionine has a hydroxyl or sulfhydryl group, this group can react with the imine to form a homoserine without peptide bond cleavage. These two cases are shown in the figure.
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See Side reactions may increase or decrease the functionality.Hans- Georg Elias: Makromoleküle: Chemische Struktur und Synthesen, S. 468 und 477 (). However, IUPAC definition and the use of the term in organic chemistry differ with respect to the functionality of a double bond. In polymer chemistry, a double bond possesses a functionality of two (because two points of contact for further polymer chains are present, on each of the two adjacent carbon atoms), while in organic chemistry the double bond is a functional group and thus has a functionality of one.
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Unwanted side reactions such as threonine and asparagine production can occur if a buildup of intermediates occurs, so scientists have developed mutant strains of C. glutamicum through PCR engineering and chemical knockouts to ensure production of side-reaction enzymes are limited. Many genetic manipulations conducted in industry are by traditional cross-over methods or inhibition of transcriptional activators. Expression of functionally active human epidermal growth factor has been brought about in C. glutamicum, thus demonstrating a potential for industrial-scale production of human proteins. Expressed proteins can be targeted for secretion through either the general secretory pathway or the twin-arginine translocation pathway.
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Coal ash is removed through in-situ gas-solid separation operation. The moving bed prevents the channeling or bypassing of the volatiles and chars, thereby maximizing the conversion of the solid fuel. The full oxidation side reactions can be impeded through the control of the oxidation state formed for the oxygen carriers in the moving bed reactor. The CLR moving bed process applied to the coal to syngas (CTS) reactions also has the flexibility of co-feeding CO2 as a feedstock with coal yielding a CO2 negative process system with a high purity of syngas production.
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Continual improvements were made to the stability and capacity of zinc–carbon cells throughout the 20th century; by the end of the century the capacities had increased fourfold over the 1910 equivalent. Improvements include the use of purer grades of manganese dioxide, better sealing, and purer zinc for the negative electrode. Zinc-chloride cells (usually marketed as "heavy duty" batteries) use a paste primarily composed of zinc chloride, which gives a longer life and steadier voltage output compared with ammonium chloride electrolyte. Side reactions due to impurities in the zinc anode increase self-discharge and corrosion of the cell.
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Some of the women experienced side effects from "the pill" (Enovid) and Edris Rice-Wray wrote Pincus and reported that Enovid "gives one hundred percent protection against pregnancy [but causes] too many side reactions to be acceptable". Pincus and Rock disagreed based on their experience with patients in Massachusetts and conducted research showing that placebos caused similar side effects. The trials went on and were expanded to Haiti, Mexico and Los Angeles despite high attrition rates, due to the large number of women eager to try this form of contraception. In May 1960, the FDA extended Enovid's approved indications to include contraception.
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As microwaves can only penetrate a short distance in materials with a high conductivity and a high permeability, microwave sintering requires the sample to be delivered in powders with a particle size around the penetration depth of microwaves in the particular material. The sintering process and side- reactions run several times faster during microwave sintering at the same temperature, which results in different properties for the sintered product. This technique is acknowledged to be quite effective in maintaining fine grains/nano sized grains in sintered bioceramics. Magnesium phosphates and calcium phosphates are the examples which have been processed through microwave sintering technique.
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Generally it is a di- or tri-thiocarbonylthio compound (1), which produces the dormant form of the radical chains. Control in RAFT polymerization (scheme 1) is achieved in a far more complicated manner than the homolytic bond formation- bond cleavage of SFRP and ATRP. The CTA for RAFT polymerization must cautiously chosen because it has an effect on polymer length, chemical composition, rate of the reaction and the number of side reactions that may occur. :600px The mechanism of RAFT begins with a standard initiation step as homolytic bond cleavage of the initiator molecule yields a reactive free radical.
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The choice of a specific nitroxide species to use has a large effect on the efficacy of an attempted polymerization. An effective polymerization (fast rate of chain growth, consistent chain length) results from a nitroxide with a fast C-O homolysis and relatively few side reactions. A more polar solvent lends itself better to C-O homolysis, so polar solvents which cannot bind to a labile nitroxide are the most effective for NMP. It is generally agreed that the structural factor that has the greatest effect on the ability of a nitroxide to mediate a radical polymerization is steric bulk.
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Using the RAFT-mediated approach to polymerize 2,2,6,6-tetramethyl-4-piperidinyl methacrylate (TMPM), the starting monomer, generates poly(2,2,6,6-tetramethyl-4-piperidnyl methacrylate) or PTMPM-RAFT. Direct oxidation of PTMPM-RAFT to PTMA is not practical, as direct oxidation causes side reactions involving the thiocaronylthiol end group of PTMPM-RAFT to react to form insoluble gel-like product. Rather, excess AIBN is used to remove the reactive terminus to form PTMPM, which can then be oxidized by meta-chloroperbenzoic acid to the desired PTMA. Despite the promise of the RAFT-mediated polymerization, reported radical concentration was only 69 ± 4%.
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A strong research focus has been placed on triggering production of excessive reactive oxygen species (ROS) using nanoparticles injected into bacterial cells. The presence of excessive ROS can stress the cell structure leading to damaged DNA/RNA, decreased membrane activity, disrupted metabolic activity, and harmful side reactions generating chemicals such as peroxides. ROS production has been induced generally through the introduction of both metal oxide and positively charged metal nanoparticles in the cell, such as iron oxides and silver. The positive charge of the metal is attracted to the negative charge of the cell membrane which it then easily penetrates.
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The seemingly simple reaction yields only 70 to 80% of impure end product due to a variety of side reactions. For example, in the chlorination of ethylene carbonate in substance or solution, 2-chloroacetaldehyde, polychlorinated ethylene carbonate and chlorinated ring- opening products are formed besides others. The separation of the by-products from the final product by distillation by thin-film evaporator, fractional recrystallization or zone melting is very expensive. The content of by- products can be reduced by stirring with sodium borohydride or ureaPCT- Anmeldung WO 2006/119910, Verfahren zur Reinigung von Vinylencarbonat, invent1: R. Langer et al.
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BOP (benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate) reagent is a reagent commonly used in the synthesis of peptides. Its use is discouraged because coupling using BOP liberates HMPA which is carcinogenic, although for small scale use in an organic laboratory this is not a great disadvantage as it is in large scale industrial usage. BOP has been used for peptide coupling, synthesis of esters, esterification of carboxylic acids, or as a catalyst. This reagent is advantageous in peptide coupling to other derived reagents because there are no side reactions from the dehydration of asparagine or glutamine.
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The chemical reactions in the cell may involve the electrolyte, the electrodes, or an external substance (as in fuel cells that may use hydrogen gas as a reactant). In a full electrochemical cell, species from one half-cell lose electrons (oxidation) to their electrode while species from the other half-cell gain electrons (reduction) from their electrode. A salt bridge (e.g., filter paper soaked in KNO3, NaCl, or some other electrolyte) is often employed to provide ionic contact between two half-cells with different electrolytes, yet prevent the solutions from mixing and causing unwanted side reactions.
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However, because of their reactivity, these same radicals can participate in unwanted side reactions resulting in cell damage. Excessive amounts of these radicals can lead to cell injury and death, which may contribute to many diseases such as cancer, stroke, myocardial infarction, diabetes and major disorders. Many forms of cancer are thought to be the result of reactions between radicals and DNA, potentially resulting in mutations that can adversely affect the cell cycle and potentially lead to malignancy. Some of the symptoms of aging such as atherosclerosis are also attributed to radical induced oxidation of cholesterol to 7-ketocholesterol.
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The rate of ligand exchange for ruthenium complexes is relatively slow in comparison with other transition metal complexes. The range of these exchange rates is around 10−2 to 10−4 s−1 which is on the scale of an average cell’s lifetime, giving the drug high kinetic stability and minimizing side reactions. This allows the Ru complex to remain intact as it approaches the target as well as remain viable throughout its interaction with the cells. It is also possible through ligand variation to precisely tune the exchange kinetics, allowing a large degree of control over the complex’s stability.
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The catalyst protonates the alkenes (propene, butene) to produce reactive carbocations, which alkylate isobutane. The reaction is carried out at mild temperatures (0-30 °C) in a two-phase reaction. Because the reaction is exothermic, cooling is needed: SAAU plants require lower temperatures so the cooling medium needs to be chilled, for HFAU normal refinery cooling water will suffice. It is important to keep a high ratio of Isobutane to Alkene at the point of reaction to prevent side reactions which produces a lower octane product, so the plants have a high recycle of Isobutane back to feed.
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Lipscomb's high-school chemistry teacher, Frederick Jones, gave Lipscomb his college books on organic, analytical, and general chemistry, and asked only that Lipscomb take the examinations. During the class lectures, Lipscomb in the back of the classroom did research that he thought was original (but he later found was not): the preparation of hydrogen from sodium formate (or sodium oxalate) and sodium hydroxide. He took care to include gas analyses and to search for probable side reactions. Lipscomb later had a high-school physics course and took first prize in the state contest on that subject.
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Although the deuterium reactions (deuterium + helium-3 and deuterium + lithium-6) do not in themselves release neutrons, in a fusion reactor the plasma would also produce D-D side reactions that result in reaction product of helium-3 plus a neutron. Although neutron production can be minimized by running a plasma reaction hot and deuterium-lean, the fraction of energy released as neutrons is probably several percent, so that these fuel cycles, although neutron-poor, do not meet the 1% threshold. See Helium-3. The D-3He reaction also suffers from the 3He fuel availability problem, as discussed above.
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P4-t-Bu is an extremely hygroscopic solid which is thermally stable up to 120 °C and chemically stable to (dry) oxygen and bases. Traces of water and protic impurities can be eliminated by addition of bromoethane. The base is both very hydrophilic and very lipophilic and can be recovered easily and almost completely from reaction mixtures by the formation of the sparingly soluble tetrafluoroborate salt. Because of its extremely weak Lewis basicity, the cation of P4-t-Bu suppresses typical side reactions of metal organyls (such as aldol condensations) as can be caused by lithium amides such as lithium diisopropylamide (LDA).
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A battery's DC–DC efficiency describes the amount of energy available to be discharged to the load connected to a battery as a proportion of the amount of energy put into the battery during charging. During charging and discharging, some of the battery's stored energy is lost as heat, and some is lost in side reactions. The lower the energy losses of a battery, the more efficient the battery is. UltraBattery's developers claim it can achieve a DC–DC efficiency of 93–95% (rate dependent) performing variability management applications in a partial SoC regime, depending on discharge rate, and 86–95% (rate dependent), when performing energy shifting applications.
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Other important side reactions include elimination of the alkyl cyanide product or alkyl halide starting material and amidine formation. The cyclization of ω-epoxy-1-nitriles provides an interesting example of how stereoelectronic factors may override steric factors in intramolecular substitution reactions. In the cyclization of 1, for instance, only the cyclopropane product 2 is observed.Corbel, B.; Durst, T. J. Org. Chem. 1976, 41, 3648. This result is attributed to better orbital overlap in the SN2 transition state for cyclization. 1,1-disubstituted and tetrasubstituted epoxides also follow this principle. (4)455px Conjugated nitriles containing γ hydrogens may be deprotonated at the γ position to give vinylogous anions.
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The model-independent evidence is compatible with a wide set of scenarios regarding the nature of the dark matter candidate and related astrophysical, nuclear and particle physics, for example: neutralinos, inelastic dark matter, self-interacting dark matter, and heavy 4th generation neutrinos, A careful quantitative investigation of possible sources of systematic and side reactions has been regularly carried out and published at the time of each data release. No systematic effect or side reaction able to account for the observed modulation amplitude and to simultaneously satisfy all the requirements of the signature has been found. The experiment has also obtained and published many results on other processes and approaches.
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Under negative pressure, power for a vacuum source is needed and the reduced boiling points of the distillates requires that the condenser be run cooler to prevent distillate vapors being lost to the vacuum source. Increased cooling demands will often require additional energy and possibly new equipment or a change of coolant. Alternatively, if positive pressures are required, standard glassware can not be used, energy must be used for pressurization and there is a higher chance of side reactions occurring in the distillation, such as decomposition, due to the higher temperatures required to effect boiling. A unidirectional distillation will rely on a pressure change in one direction, either positive or negative.
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Neutrino losses start to become a major factor in the fusion processes in stars at the temperatures and densities of carbon burning. Though the main reactions don't involve neutrinos, the side reactions such as the proton- proton chain reaction do. But the main source of neutrinos at these high temperatures involves a process in quantum theory known as pair production. A high energy gamma ray which has a greater energy than the rest mass of two electrons (mass-energy equivalence) can interact with electromagnetic fields of the atomic nuclei in the star, and become a particle and anti-particle pair of an electron and positron.
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The Bunsen reaction is a chemical reaction that describes water, sulfur dioxide, and iodine reacting to form sulfuric acid and hydrogen iodide: : 2H2O + SO2 \+ I2 → H2SO4 \+ 2HI This reaction is the first step in the sulfur- iodine cycle to produce hydrogen. The products separate into two aqueous layers, with the sulfuric acid floating on top, and a mixture of hydrogen iodide and unreacted iodine on the bottom. While the two layers are generally considered immiscible, small amounts of sulfuric acid may still remain in the hydrogen iodide layer and vice versa. This can lead to unwanted side reactions, one of which precipitates out sulfur, a potential obstruction to the reaction vessel.
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Definition of Weapons-Usable Uranium-233 ORNL/TM-13517 While U-233 would thus seem ideal for weaponization, a significant obstacle to that goal is the co-production of trace amounts of uranium-232 due to side-reactions. U-232 hazards, a result of its highly radioactive decay products such as thallium-208, are significant even at 5 parts per million. Implosion nuclear weapons require U-232 levels below 50 PPM (above which the U-233 is considered "low grade"; cf. "Standard weapon grade plutonium requires a Pu-240 content of no more than 6.5%." which is 65,000 PPM, and the analogous Pu-238 was produced in levels of 0.5% (5000 PPM) or less).
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During operation, conventional VRLA batteries must be refreshed (overcharged) to dissolve the sulfate crystals that have accumulated on the negative electrode and replenish the capacity of the battery. Refreshing the battery also helps return the battery cells in the string (where multiple batteries are used together) to a consistent operating voltage. However the overcharging process is complicated by the fact that not only is the battery out of service during refresh cycles, but the high currents required to complete the overcharge process (within a reasonable timeframe) are also the cause of various parasitic losses. These include thermal losses and losses due to various side reactions (chiefly hydrogen evolution, oxygen evolution and grid corrosion).
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Arguably the biggest drawback of the vinylcyclopropane rearrangement as a synthetic method is its intrinsically high activation barrier resulting in very high reaction temperatures (500-600 °C). Not only do these high temperatures allow side reactions with similar activation energies, such as homodienyl-1,5]-hydrogen shifts, to occur but also do they significantly limit the functional groups tolerated in the substrates. It was well recognized by the chemical community that in order for this reaction to become a useful synthetic method, hopefully applicable in complex natural product settings at some point, some reaction development had to be done. Some of the earliest attempts to improve the vinylcyclopropane rearrangement as a synthetic method came from the Corey group in 1972.
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As described above, the use of N-terminal and side chain protecting groups is essential during peptide synthesis to avoid undesirable side reactions, such as self-coupling of the activated amino acid leading to (polymerization). This would compete with the intended peptide coupling reaction, resulting in low yield or even complete failure to synthesize the desired peptide. Two principle orthogonal protecting group schemes exist for use in solid-phase peptide synthesis: so-called Boc/Bzl and Fmoc/tBu approaches. The Boc/Bzl strategy utilizes TFA-labile N-terminal Boc protection alongside side chain protection that is removed using anhydrous hydrogen fluoride during the final cleavage step (with simultaneous cleavage of the peptide from the solid support).
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Scavengers such as water and triisopropylsilane (TIPS) are added during the final cleavage in order to prevent side reactions with reactive cationic species released as a result of side chain deprotection. The resulting crude peptide is obtained as a TFA salt, which is potentially more difficult to solubilize than the fluoride salts generated in Boc SPPS. Fmoc/tBu SPPS is less atom-economical, as the fluorenyl group is much larger than the Boc group. Accordingly, prices for Fmoc amino acids were high until the large-scale piloting of one of the first synthesized peptide drugs, enfuvirtide, began in the 1990s, when market demand adjusted the relative prices of Fmoc- vs Boc- amino acids.
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The Gomberg–Bachmann reaction, named for the Russian-American chemist Moses Gomberg and the American chemist Werner Emmanuel Bachmann, is an aryl-aryl coupling reaction via a diazonium salt.W. Pötsch. Lexikon bedeutender Chemiker (VEB Bibliographisches Institut Leipzig, 1989) () :Gomberg-Bachmann reaction The arene compound 1 (here benzene) is coupled with base with the diazonium salt 2 to the biaryl 3 through an intermediate aryl radical. For example, p-bromobiphenyl may be prepared from 4-bromoaniline and benzene: : BrC6H4NH2 \+ C6H6 → BrC6H4−C6H5 The reaction offers a wide scope for both diazonium component and arene component but yields are generally low following the original procedure (less than 40%), given the many side-reactions of diazonium salts.
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This unique metal coordination mode can prevent a number of possible side reactions associated with cis-coordination, and results in a more effective and selective catalytic process. Although cis-coordination is requisite for many catalytic processes, it is not required for catalytic cyclopropanation/aziridnation or atom/group transfer reactions. Third, it has been well documented that the physical and chemical properties of a porphyrin complex of a given metal ion can be systematically tuned by introducing peripheral substituents with varied electronic, steric, and conformational environments on the aromatic ring structure of the porphyrin ligand. X. Peter Zhang's group have accomplished porphyrin modification by using palladium- catalyzed coupling processes of chiral amides on bromoporphyrin templates.
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Lipases make ideal enzymes for these applications because they are highly selective in their activity, they are readily produced and secreted by bacteria and fungi, their crystal structure is well characterized, they do not require cofactors for their enzymatic activity, and they do not catalyze side reactions. The range of uses of lipases encompasses production of biopolymers, generation of cosmetics, use as a herbicide, and as an effective solvent. However, perhaps the most well known use of lipases in this field is its use in the production of biodiesel fuel. In this role, lipases are used to convert vegetable oil to methyl- and other short-chain alcohol esters by a single transesterification reaction.
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The most prominent biomolecular engineering technique seen in this primer design method is the initial bioimmobilization of a nucleotide to a solid support. This step is commonly done via the formation of a covalent bond between the 3’-hydroxy group of the first nucleotide of the primer and the solid support material. Furthermore, as the DNA primer is created certain functional groups of nucleotides to be added to the growing primer require blocking to prevent undesired side reactions. This blocking of functional groups as well as the subsequent de-blocking of the groups, coupling of subsequent nucleotides, and eventual cleaving from the solid support are all methods of manipulation of biomolecules that can be attributed to biomolecular engineering.
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This technique allows a reaction vessel to be heated throughout with minimal stirring, as opposed to heating the bottom of the vessel and waiting for convection to heat the remainder, cutting down on both the duration of the reaction and the possibility of side reactions that may occur at higher temperatures. A variation on this theme is the water bath in which the sand is replaced with water. It can be used to keep a reaction vessel at the temperature of boiling water until all water is evaporated (see Standard enthalpy change of vaporization). Sand baths are one of the oldest known pieces of laboratory equipment, having been used by the alchemists.
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The hydrogen must be isotopically pure and the influx of impurities into the plasma must be controlled to prevent neutron-producing side reactions such as: :11B + d → 12C + n + 13.7 MeV :d + d → 3He + n + 3.27 MeV The shielding design reduces the occupational dose of both neutron and gamma radiation to operators to a negligible level. The primary components would be water to moderate the fast neutrons, boron to absorb the moderated neutrons and metal to absorb X-rays. The total thickness is estimated to be about one meter, mostly water.El Guebaly, Laial, A., Shielding design options and impact on reactor size and cost for the advanced fuel reactor Aploo, Proceedings- Symposium on Fusion Engineering, v.
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In order to maintain and promote the proper processing of a clarifier, it is important to remove any corrosive, reactive and polymerisable component first, or any material that may foul the outlet stream of water to avoid any unwanted side reactions, changes in the product or cause damage to any of the water treatment equipment. This is done by routine inspections and the frequent cleaning of the quiescent zones and the inlet and outlet areas of the clarifier in order to ascertain the extent of sediment build up and to clean and remove any scouring, litter, weeds or debris that may have accumulated over time.Western Regional Aquaculture Center, University of Washington. Seattle, WA (2001).
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It was observed in HRTEM images that indium thin films decorate some of the facets of the gold nanoparticle. The promoting effect on selectivity might result from the fact that only the Au sites that promote side-reactions are decorated by In. A strategy that in many reactions has succeeded at improving gold's catalytic activity without impairing its selectivity is to synthesize bimetallic Pd-Au or Pt-Au catalysts. For the hydrogenation of 1,3-butadiene to butenes, model surfaces of Au(111), Pd-Au(111), Pd-Au(110), and Pd(111) were studied with LEED, AES, and LEIS. A selectivity of ~100% was achieved on Pd70Au30(111) and it was suggested that Au might promote the desorption of the product during the reaction.
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However, interfering signals can be observed due to side reactions of the matrix with the sample, such as in the case of the matrix interacting with alkali metal ions which can impair the analysis of the spectra. Typically the amount of salt in the matrix only becomes a problem in very high concentrations, such as 1 molar. The problem of having too high a concentration of salt in the sample can be solved by first running the solution through liquid chromatography to help purify the sample, but this method is time consuming and results in the loss of some of the sample to be analyzed. Another method is focused on purification once the sample solution is deposited onto the sample probe.
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Neosporol is a natural product that includes a 1,3-dioxolane moiety, and is an isomer of sporol which has a 1,3-dioxane ring. The total synthesis of both compounds has been reported, and each includes a step in which a dioxolane system is formed using trifluoroperacetic acid (TFPAA), prepared by the hydrogen peroxide - urea method. This method involves no water, so it gives a completely anhydrous peracid, necessary in this case as the presence of water would lead to unwanted side reactions. : \+ -> \+ \+ In the case of neosporol, a Prilezhaev reaction with trifluoroperacetic acid is used to convert a suitable allyl alcohol precursor to an epoxide, which then undergoes a ring-expansion reaction with a proximate carbonyl functional group to form the dioxolane ring.
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Thermal ene reactions have several drawbacks, such as the need for very high temperatures and the possibility of side reactions, like proton-catalyzed olefin polymerization or isomerization reactions. Since enophiles are electron-deficient, it was reasoned that their complexation with Lewis acids should accelerate the ene reaction, as it occurred for the reaction shown in Figure 8. Figure 8: Improvements brought to the ene reaction by Lewis acid catalysis Alkylaluminum halides are well known as proton scavengers, and their use as Lewis acid catalysts in ene reactions has greatly expanded the scope of these reactions and has allowed their study and development under significantly milder conditions. Since a Lewis acid can directly complex to a carbonyl oxygen, numerous trialkylaluminum catalysts have been developed for enophiles that contain a C=O bond.
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Molecular chaperones are an essential class of proteins that aid other proteins to obtain their biologically active structure and inhibit off-pathway side reactions during protein maturation.Buchner J, Kiefhaber T, Protein Folding Handbook, WILEY-VCH Verlag, Weinheim, 2005 Buchner’s work focuses on understanding mechanisms of molecular chaperones in a quantitative and mechanistic manner. His work has contributed to our understanding of the chaperone cycle of the bacterial chaperone GroELSchmidt M, Rutkat K, Rachel R, Pfeifer G, Jaenicke R, Viitanen P, Lorimer G, Buchner J (1994) Science 265:656-9 and now lays a particular emphasis on small heat shock proteins (sHsps), the Hsp90 chaperone machinery and the role of molecular chaperones in antibody folding. Buchner’s work established sHsps as molecular chaperonesJakob U, Gaestel M, Engel K, Buchner J (1993) J Biol Chem. 268:1517-20.
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To avoid undesired side reactions, reactive hydroxy and exocyclic amino groups present in natural or synthetic nucleosides are appropriately protected. As long as a nucleoside analog contains at least one hydroxy group, the use of the appropriate protecting strategy allows one to convert that to the respective phosphoramidite and to incorporate the latter into synthetic nucleic acids. To be incorporated in the middle of an oligonucleotide chain using phosphoramidite strategy, the nucleoside analog must possess two hydroxy groups or, less often, a hydroxy group and another nucleophilic group (amino or mercapto). Examples include, but are not limited to, alternative nucleotides, LNA, morpholino, nucleosides modified at the 2'-position (OMe, protected NH2, F), nucleosides containing non-canonical bases (hypoxanthine and xanthine contained in natural nucleosides inosine and xanthosine, respectively, tricyclic bases such as G-clamp, etc.) or bases derivatized with a fluorescent group or a linker arm.
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Trifluoroperacetic acid can be easily prepared by an Organic Syntheses process of treating trifluoroacetic anhydride with a concentrated (90%) aqueous solution of hydrogen peroxide: : \+ -> \+ As the anhydride will form trifluoroacetic acid in contact with water, an excess of the anhydride also serves to remove the solvent from the peroxide reactant: : \+ -> 2 A more dilute hydrogen peroxide solution (30%) can be used to form trifluoroperacetic acid for some reactions from trifluoroacetic acid. : \+ -> \+ In order to avoid the danger of handling pure or highly concentrated solutions of hydrogen peroxide, hydrogen peroxide – urea can be used to give the peracid. This method involves no water, so it gives a completely anhydrous peracid, which is an advantage when the presence of water leads to side reactions during certain oxidation reactions. : \+ -> \+ \+ In cases where a pH buffering agent is needed for a synthesis and where the presence of water is tolerated, another approach has been developed.
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The catalyst is the most important component of ATRP because it determines the equilibrium constant between the active and dormant species. This equilibrium determines the polymerization rate. An equilibrium constant that is too small may inhibit or slow the polymerization while an equilibrium constant that is too large leads to a wide distribution of chain lengths. There are several requirements for the metal catalyst: #There needs to be two accessible oxidation states that are differentiated by one electron #The metal center needs to have reasonable affinity for halogens #The coordination sphere of the metal needs to be expandable when it is oxidized as to accommodate the halogen #The transition metal catalyst should not lead to significant side reactions, such as irreversible coupling with the propagating radicals and catalytic radical termination The most studied catalysts are those that include copper, which has shown the most versatility with successful polymerizations for a wide selection of monomers.
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In a zinc–carbon dry cell, the outer zinc container is the negatively charged terminal. The zinc is oxidised by the charge carrier, chloride (Cl−), via the following half-reactions: Anode (oxidation reaction, marked −) : Zn + 2 Cl− → ZnCl2 \+ 2 e− Cathode (reduction reaction, marked +) : 2 MnO2 \+ 2 NH4Cl + H2O + 2 e− → Mn2O3 \+ 2 NH4OH + 2 Cl− Other side reactions are possible, but the overall reaction in a zinc–carbon cell can be represented as : Zn + 2 MnO2 \+ 2 NH4Cl + H2O → ZnCl2 \+ Mn2O3 \+ 2 NH4OH If zinc chloride is substituted for ammonium chloride as the electrolyte, the anode reaction remains the same: : Zn + 2 Cl− → ZnCl2 \+ 2 e− and the cathode reaction produces zinc hydroxide instead of ammonium hydroxide: : 2 MnO2 \+ ZnCl2 \+ H2O + 2 e− → Mn2O3 \+ Zn(OH)2 \+ 2 Cl− giving the overall reaction : Zn + 2 MnO2 \+ H2O → Mn2O3 \+ Zn(OH)2 The battery has an electromotive force (e.m.f.) of about 1.5 V. The approximate nature of the e.m.f is related to the complexity of the cathode reaction.
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Research conducted by independent laboratories, such as the United States's Sandia National Laboratories, the Advanced Lead-Acid Battery Consortium (ALABC), the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and commercial tests by East Penn Manufacturing, Furukawa Battery and Ecoult indicate that in comparison with conventional valve regulated lead acid (VRLA) batteries, UltraBattery technology has higher energy efficiencies, a longer lifetime and superior charge acceptance under partial state of charge (SoC) conditions. Combining the two technologies in one battery cell means that UltraBattery works very efficiently compared with conventional lead acid technologies largely due to the fact that it can be operated for long periods in a partial state of charge (pSoC), whereas conventional lead acid batteries are more typically designed for high SoC use (i.e. when the battery is close to fully charged). Operating in the partial SoC range extends the battery's life chiefly by reducing sulfation and by reducing time spent operating at very high and very low states of charge, where various side reactions tend to cause deterioration.
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