Single bimolecular reactions

Single Bimolecular Reaction in a Tubular Reactor Mixing Effects on Conversion ... 

Studying three-dimensional systems Pota has shown (Pota, 1985), again using Dulac-type theorems, that there only exists a single bimolecular reaction which may exhibit oscillatory behaviour, and this is the Ivanova reaction ... 

The results of computations, even with the simplest model (12), are quite realistic. The ref. [15] gives calculations of a single bimolecular reaction within a well stirred reactor. The ref. [16] shows the shape of P((j>) computed with the Curl model and the values of mean mass fraction that are obtained, with the assumption of very fast reactions, within a diffusion jet flame the agreement with experiments appears quite satisfactory. 

Leonard and Hill [34] have recently performed such a simulation, in the case of a single bimolecular reaction, starting from an initial state with A and B perfectly segregated. The fig. 3 shows the time evolution of... 

Although not completely understood, hormone binding to the specific receptors is rapid, reversible and may be depicted as a single, bimolecular reaction as follows ... 

Perhaps the single most important piece of information to be derived from a kinetic study is the composition of the transition state. The basis of the inference can be developed by means of this elementary bimolecular reaction. 

These apply to a bimolecular reaction in which two reactant molecules become a single particle in the transition state. It is evident from Eqs. (6-20) and (6-21) that a change in concentration scale will result in a change in the magnitude of AG. An Arrhenius plot is, in effect, a plot of AG against 1/T. Because a change in concentration scale alters the intercept but not the slope of an Arrhenius plot, we conclude that the values of AG and A, but not of A//, depend upon the concentration scale employed for the expression of reactant concentrations. We, therefore, wish to know which concentration scale is the preferred one in the context of mechanistic interpretation, particularly of AS values. 

FIGURE 13.16 A representation of a proposed one-step mechanism for the decomposition of ozone in the atmosphere. This reaction takes place in a single bimolecular collision. 

These should be simple unlmolecular or bimolecular reactions yielding a single or at most two reaction paths. Rates may therefore be fit using Langmuir-Hinshelwood (LH) rate expressions. For A —> products this should be... 

For the simple bimolecular reaction involving a single class of binding site, the onset of binding should also contain an exponential term. Thus,... 

The number of chemical species involved in a single elementary reaction is referred to as the molecularity of that reaction. Molecularity is a theoretical concept, whereas stoichiometry and order are empirical concepts. A simple reaction is referred to as uni-, bi-, or termolecular if one, two, or three species, respectively, participate as reactants. The majority of known elementary steps are bimolecular, with the balance being unimolecular and termolecular. 

Thus mechanism B, which consists solely of bimolecular and unimolecular steps, is also consistent with the information that we have been given. This mechanism is somewhat simpler than the first in that it does not requite a ter-molecular step. This illustration points out that the fact that a mechanism gives rise to the experimentally observed rate expression is by no means an indication that the mechanism is a unique solution to the problem being studied. We may disqualify a mechanism from further consideration on the grounds that it is inconsistent with the observed kinetics, but consistency merely implies that we continue our search for other mechanisms that are consistent and attempt to use some of the techniques discussed in Section 4.1.5 to discriminate between the consistent mechanisms. It is also entirely possible that more than one mechanism may be applicable to a single overall reaction and that parallel paths for the reaction exist. Indeed, many catalysts are believed to function by opening up alternative routes for a reaction. In the case of parallel reaction paths each mechanism proceeds independently, but the vast majority of the reaction will occur via the fastest path. 

Rate Expressions for Enzyme Catalyzed Single-Substrate Reactions. The vast majority of the reactions catalyzed by enzymes are believed to involve a series of bimolecular or unimolecular steps. The simplest type of enzymatic reaction involves only a single reactant or substrate. The substrate forms an unstable complex with the enzyme, which subsequently undergoes decomposition to release the product species or to regenerate the substrate. 

The electron-transfer paradigm for chemical reactivity in Scheme 1 (equation 8) provides a unifying mechanistic basis for various bimolecular reactions via the identification of nucleophiles as electron donors and electrophiles as electron acceptors according to Chart 1. Such a reclassification of either a nucleophile/ electrophile, an anion/cation, a base/acid, or a reductant/oxidant pair under a single donor/acceptor rubric offers a number of advantages previously unavailable, foremost of which is the quantitative prediction of reaction rates by invoking the FERET in equation (104). 

Note that both of the steps in the mechanism are bimolecular reactions, reactions that involve the collision of two chemical species. Unimolecular reactions are reactions in which a single chemical species decomposes or rearranges. Both bimolecular and unimolecular reactions are common, but the collision of three or more chemical species (termolecular) is quite rare. Thus, in developing or assessing a mechanism, it is best to consider only unimolecular or bimolecular elementary steps. 

Steric constraints dictate that reactions of organohalides catalysed by square planar nickel complexes cannot involve a cw-dialkyl or diaryl Ni(iii) intermediate. The mechanistic aspects of these reactions have been studied using a macrocyclic tetraaza-ligand [209] while quantitative studies on primary alkyl halides used Ni(n)(salen) as catalyst source [210]. One-electron reduction affords Ni(l)(salen) which is involved in the catalytic cycle. Nickel(l) interacts with alkyl halides by an outer sphere single electron transfer process to give alkyl radicals and Ni(ii). The radicals take part in bimolecular reactions of dimerization and disproportionation, react with added species or react with Ni(t) to form the alkylnickel(n)(salen). Alkanes are also fonned by protolysis of the alkylNi(ii). 

Organic chemists have long known of bimolecular reactions in which two molecules create a single larger one. The most common of these are formation of esters from acid and alcohol, such as the reaction of ethanol with acetic acid to form ethyl acetate... 

Kersey FR, Yount WC, Craig SL. Single-molecule force spectroscopy of bimolecular reactions system homology in the mechanical activation of ligand substitution reactions. J Am Chem Soc 2006 128 3886-3887. 

Bimolecular reactions having more products than the single species produced from a condensation are also possible, and their rate laws are constructed and measured in a fashion analogous to Eqs. (15.12) and (15.13). Note that the special case of a bimolecular reaction involving two molecules of the same reactant has a rate law that is particularly simple to integrate and work with. 

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