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Cyclic reactions

An important point about kinetics of cyclic reactions is tliat if an overall reaction proceeds via a sequence of elementary steps in a cycle (e.g., figure C2.7.2), some of tliese steps may be equilibrium limited so tliat tliey can proceed at most to only minute conversions. Nevertlieless, if a step subsequent to one tliat is so limited is characterized by a large enough rate constant, tlien tire equilibrium-limited step may still be fast enough for tire overall cycle to proceed rapidly. Thus, tire step following an equilibrium-limited step in tire cycle pulls tire cycle along—it drains tire intennediate tliat can fonn in only a low concentration because of an equilibrium limitation and allows tire overall reaction (tire cycle) to proceed rapidly. A good catalyst accelerates tire steps tliat most need a boost. [Pg.2700]

Atoms and free radicals are highly reactive intermediates in the reaction mechanism and therefore play active roles. They are highly reactive because of their incomplete electron shells and are often able to react with stable molecules at ordinary temperatures. They produce new atoms and radicals that result in other reactions. As a consequence of their high reactivity, atoms and free radicals are present in reaction systems only at very low concentrations. They are often involved in reactions known as chain reactions. The reaction mechanisms involving the conversion of reactants to products can be a sequence of elementary steps. The intermediate steps disappear and only stable product molecules remain once these sequences are completed. These types of reactions are refeiTcd to as open sequence reactions because an active center is not reproduced in any other step of the sequence. There are no closed reaction cycles where a product of one elementary reaction is fed back to react with another species. Reversible reactions of the type A -i- B C -i- D are known as open sequence mechanisms. The chain reactions are classified as a closed sequence in which an active center is reproduced so that a cyclic reaction pattern is set up. In chain reaction mechanisms, one of the reaction intermediates is regenerated during one step of the reaction. This is then fed back to an earlier stage to react with other species so that a closed loop or... [Pg.16]

How can we predict whether conrotatory or disrotatory motion will occur in a given case According to frontier orbital theory, the stereochemistry of an electro-cyclic reaction is determined by the symmetry of the polyene HOMO. The electrons in the HOMO are the highest-energy, most loosely held electrons, and are therefore most easily moved during reaction. For thermal reactions, the ground-state... [Pg.1183]

The following reaction takes place in two steps, one of which is a cycloaddition and the other of which is a reverse cycloaddition. Identify the two peri-cyclic reactions, and show how they occur. [Pg.1203]

Cycioaddition reaction (Sections 14.4, 30.6) A peri cyclic reaction in which two reactants add together in a single step to yield a cyclic product. The Diels-Alder reaction between a diene and a dienophile to give a cyclohexene is an example. [Pg.1239]

Electrocyclic reaction (Section 30.3) A unimolecular peri-cyclic reaction in which a ring is formed or broken by a concerted reorganization of electrons through a cyclic transition state. For example, the cyciization of 1,3.5-hexatriene to yield 1,3-cyclohexadiene is an electrocyclic reaction. [Pg.1240]

The polyene character of 1 /7-azcpines makes them susceptible not only to a variety of electro-cyclic reactions, but also to cycloaddition with a variety of dienophiles, and to dimerization by [6 + 4] 7i-pericyclic reactions. [Pg.186]

A special method, with only two examples, starts from 1,2,4-triazines.20 21 Diels-Alder reaction with the strained dienophile dimethyl tricyclo[4.2.2.02,5]deca-3,7,9-triene-7,8-dicarboxylate (14) is followed by an elimination of nitrogen via a retro-Diels-Alder process. The formed product, however, cannot be isolated, but reacts via another retro-Diels-Alder reaction and an electro-cyclic reaction to provide the azocine derivative 15. The sequence order of the reactions is not clear, but both pathways lead to the same product. [Pg.513]

The Cyclic Reaction Sequence Generates FADH2 NADH... [Pg.181]

Step 2. Every reaction pathway in the reaction scheme involving five arrows, by which a particular enzyme species might be formed, is constructed. The concentration of a particular enzyme species is given by the sum of the rate constant products for that enzyme form. Consideration of the above cyclic reaction scheme yields the relationships given in Table A17.1. [Pg.682]

When the reactions of alkane molecules larger than the butanes or neopentane are studied, and in particular when the molecule is large enough to form a Cs or a Ce ring, the complexity of the reaction pathway is considerably increased and an important feature is the occurrence, in addition to isomerization product, of important amounts of cyclic reaction products, particularly methylcyclopentane, formed by dehydrocycliza-tion this suggests the existence of adsorbed cyclic species. The question is whether the reaction paths for dehydrocyclization and isomerization are related. There is convincing evidence that they are. Skeletal interconversions involving n-hexane, 2- and 3-methylpentane may be represented. [Pg.37]

ODHP performance under cyclic reaction-regeneration... [Pg.375]

The application of the Woodward-Hoffmann theory 22> of electro-cyclic reactions to chemiluminescence has proved a very useful and productive approach, suggested independently by E. H. White and M. J. C. Harding 23>, F. Me Capra, D. G. Richardson, and Y. C. Chang u> 24>, and M. M. Rauhut and coworkers 25>. [Pg.71]

The catalysis of hydrogen peroxide decomposition by iron ions occupies a special place in redox catalysis. This was precisely the reaction for which the concept of redox cyclic reactions as the basis for this type of catalysis was formulated [10-13]. The detailed study of the steps of this process provided a series of valuable data on the mechanism of redox catalysis [14-17]. The catalytic decomposition of H202 is an important reaction in the system of processes that occur in the organism [18-22]. [Pg.385]

A decisive factor in making one salt and one acid the more stable might be the conjugation of the double bonds in the favored structures. A concerted, and sometimes cyclic, reaction of the predominant salt would give the less stable acid ... [Pg.201]

The dehydrogenative route is probably identical with the alkene-alkyl insertion mechanism (I5a) (Scheme IVA) rather than with the dicarbyne cyclization (85a). The latter was based on the unreactivity of -hexane in C5 cyclic reactions over iridium (4Ia). [Pg.296]

C5 cyclization requires stricter geometric conditions than aromatization. This is in favor of the dual-site mechanism of C5 cyclic reactions (25). All metals catalyzing it have an fee lattice, and their atomic diameter lies between 0.269 and 0.277 nm. These two criteria must be fulfilled simultaneously. With such a distance between the two sites, the screening of the C—C bond adjacent to the preferably adsorbed tertiary C atom becomes evident. Figure... [Pg.319]

The assumption of reactive chemisorption may be useful for the surface intermediate of C5 cyclic reactions. It may well be possible that a competition occurs between a reactive and a dissociative chemisorption the former giving C5 the latter cyclic products. There is a thermodynamic relationship between these two surface species (see Section II,A,2). Scheme XIII summarizes all the above-mentioned facts about hydrogen effects and various surface intermediates (31). [Pg.324]

If hydrogen occupies all sites, the dual-site mechanism may operate over two adjacent /2g sites 42). The importance of active site periodicity and the screening of the adjacent C—C bond is valid in this case, too. This (assumedly adsorbed) hydrogen does not participate in C5 cyclic reactions. There is some indication, however, that it might be mobilized for cyclobutane ring opening 97, 97a). [Pg.326]

One carbon atom in a wrong interstice may block the C5 cyclization activity of several surrounding sites. Therefore, C5 cyclic reactions are suppressed first during catalyst deactivation, while aromatization activity lasts much longer 159). This again supports the reactive adsorption mechanism 154). A different type of deactivation was reported as being due to disordered and ordered surface carbonaceous deposits 138,148). [Pg.326]

Although these equations held true for some strains of bacteria under some growth conditions, they did not help explain the commonly observed quantitative conversion of both sulfur atoms of thiosulfate to sulfate, rather than the liberation of the sulfane-sulfur mainly as elemental sulfur. During the 1960s, cyclic reactions of polythionates and other polysulfur compounds continued to be postulated as mechanisms for thiosulfate and polythionate metabolism (Trudinger 1967), but none of these was supported at the time by strong biochemical evidence. The time was opportune for a new approach to the problem of thiosulfate oxidation in thiobacilli. [Pg.206]

In the vertebrates, biosynthesis of fatty acids is catalyzed by fatty add synthase, a multifunctional enzyme. Located in the cytoplasm, the enzyme requires acetyl CoA as a starter molecule. In a cyclic reaction, the acetyl residue is elongated by one C2 unit at a time for seven cycles. NADPH+H is used as a reducing agent in the process. The end product of the reaction is the saturated Cie acid, palmitic acid. [Pg.168]

Most of the peracetic acid decomposes via a cyclic reaction with acetaldehyde to form two moles of acetic acid. [Pg.151]


See other pages where Cyclic reactions is mentioned: [Pg.1198]    [Pg.211]    [Pg.159]    [Pg.35]    [Pg.246]    [Pg.374]    [Pg.31]    [Pg.31]    [Pg.43]    [Pg.51]    [Pg.61]    [Pg.84]    [Pg.375]    [Pg.376]    [Pg.578]    [Pg.591]    [Pg.619]    [Pg.14]    [Pg.152]    [Pg.321]    [Pg.324]    [Pg.325]    [Pg.328]    [Pg.55]    [Pg.310]    [Pg.51]    [Pg.61]   
See also in sourсe #XX -- [ Pg.28 ]




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1,3-dipolar cycloaddition reactions cyclic nitrones

5N2 mechanism cyclic ether reactions

Acetals, cyclic, reaction with acyl trifluoroacetates

Activation energy cyclic ether reactions

Addition reactions, cyclic alkynes

Alkene derivatives diastereoselective cyclic reactions

Amine reactions with cyclic anhydride

Anhydrides cyclic, reaction with alcohols

Anhydrides, cyclic, reaction with hydrazine

Asymmetric reactions cyclic allyl alcohol derivatives

Bromine, reaction with cyclic acetals

Bromonium ions, cyclic, addition reactions with alkenes forming

Butyllithium, reaction with cyclic acetals

Carbonyl halides, reactions with ether, cyclic

Carbonylation diastereoselective cyclic reactions

Cheletropic reactions, cyclic

Cheletropic reactions, cyclic sulfones

Cope elimination reaction cyclic amines

Coupled homogeneous chemical reaction cyclic voltammetry

Cyclic Enzyme Reactions

Cyclic Heck Reactions, Noteworthy Variations

Cyclic Polymers Obtained by the CuAAC Click Reaction

Cyclic acetal polymerization reaction

Cyclic acid-base bifunctional reaction

Cyclic aldol reaction

Cyclic alkene reaction

Cyclic alkynes from elimination reactions

Cyclic alkynes from ring-closure reactions

Cyclic aminals 3+2] cycloaddition reactions

Cyclic amines reactions

Cyclic anhydride, reaction with epoxy

Cyclic anhydrides reaction with ammonia

Cyclic carbodiimides reactions

Cyclic carbonates, allylation reactions

Cyclic compounds Diels-Alder reaction)

Cyclic compounds Wurtz reaction

Cyclic dendralenes reaction

Cyclic electrode reactions

Cyclic elimination reactions

Cyclic enamines radical reactions

Cyclic ethers, reactions

Cyclic homogeneous chemical reactions

Cyclic hydroxamic acids reactions

Cyclic imines, Staudinger reaction

Cyclic imino Diels-Alder reaction

Cyclic ketones, Michael reactions

Cyclic nitrones, reaction with

Cyclic nucleophilic addition reactions

Cyclic phosphorus compounds, reaction

Cyclic phosphorus compounds, reaction pathway

Cyclic reaction products

Cyclic reaction with cuprates

Cyclic reaction with diethyl malonate

Cyclic reaction with nucleophiles

Cyclic reaction with organocuprates

Cyclic reactions and

Cyclic reactions with diazoalkanes

Cyclic ring-closure reactions

Cyclic sulfates reactions

Cyclic sulfates ring opening reactions

Cyclic transition state, aldol reaction

Cyclic transition state, for aldol reaction

Cyclic transition states in reactions

Cyclic voltammetry coupled homogeneous electrode reactions

Cyclic voltammetry coupled homogeneous reactions

Cyclic voltammetry nemstian reaction

Cyclic voltammetry quasireversible reactions

Cyclic voltammetry reaction order approach

Cyclic voltammetry single electron transfer reactions

Cycloaddition reactions cyclic nitronate preparation

Diels-Alder reaction with cyclic dienes

Diels-Alder reactions cyclic dienes: furans

Diels-Alder reactions of cyclic ketones

Electro cyclic reactions

Electro cyclic reactions photochemical

Elimination reactions, cyclic alkynes

Enantioselectivity cyclic ether reactions

Enones, cyclic, photochemical reactions

Epoxides Cyclic three-membered ring ethers reactions

Friedel-Crafts reaction with cyclic anhydrides

Heck reactions cyclic

Hydrogen fluoride, reaction with cyclic

Intermolecular Cyclic Transition State Reactions

Intermolecular Reactions with Cyclic Transition States

Iron catalysis cyclic ether reactions

Irreversible electrode reaction cyclic voltammetry

Irreversible reaction cyclic voltammetry

Isocyanates reaction with cyclic anhydrides

Ketones cyclic imines, reactions with

Ketones cyclic, photochemical reactions

Kinetic studies cyclic ether reactions

Lewis acids reaction with cyclic acetals

Lithium, butyl-, reaction with cyclic

Meso-cyclic anhydrides reactions

Michael reaction cyclic enone acceptor

Michael reactions, asymmetric cyclic enones

Molecular Reactions Cyclic Transition States

Multiple-electrode reactions cyclic voltammetry

Nucleophile effects cyclic ether reactions

Nucleophilic aliphatic substitution cyclic ether reactions

Olefins cyclic, metathesis reactions

Organometallic compounds reactions with cyclic ketones

Orthoformic reaction with esters, cyclic

Oxygen reduction reaction cyclic voltammogram

Peri cyclic reactions

Photocycloaddition/trapping reactions, cyclic dienones

Polymers, cyclic formation reaction

Product studies cyclic ether reactions

Quasi-reversible reactions, cyclic

Quasi-reversible reactions, cyclic voltammetry

REACTIONS OF CYCLIC HYDROCARBONS

Radical Reactions. Newly Emerged Tools for the Synthesis of Cyclic Compounds

Reaction intermediates, cyclic

Reaction of Cyclic Ketals with Carbon Dioxide

Reaction of Isocyanates with Cyclic Anhydrides

Reaction of Wood with Cyclic Anhydrides

Reaction with cyclic 1,3-diketones

Reaction with cyclic anhydrides

Reaction with cyclic ethers

Reaction with cyclic-tetramer

Reactions involving cyclic transition states

Reactions of Cyclic Alkanes with Hydrogen

Reactions of cyclic alkynes with metal compounds

Reactions of excited cyclic hydrocarbons

Reactions with Cyclic Acetals

Reactions with Cyclic Transition States

Rearrangement Reactions of Cyclic Unsaturated Ketones

Recombination processes cyclic reactions

Redox reactions cyclic voltammograms

Regioselectivity cyclic ether reactions

Reversible reaction cyclic voltammetry

Ring-closure reactions, cyclic alkynes

SnI reactions in cyclic systems

Solvent effects cyclic ether reactions

Stereochemistry cyclic ether reactions

Stereoselective reactions of cyclic compounds

Stereoselectivity of Radical Reactions Cyclic Systems

Substitution reactions cyclic allylic esters

Sulfone, methoxymethyl phenyl reaction with cyclic ketones

Sulfoxides, vinyl via reactions of allyl phenyl sulfoxide with cyclic

Transition state structures cyclic ether reactions

Trimethyl phosphite, reaction with cyclic

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