Reagents rate constants

Using the principle of detailed balancing for the processes of adsorption (rate constant dkitd E)) and AB/s/( E) decomposition back to reagents (rate constant k (E)) F(E, t) can be represented in the form... 

Compound Medium Reagent Rate Constant [10 °M- s- ] Product Maximum [nm]... 

In the inverse problem of chemical kinetics kinetic parameters of the reaction (reaction orders for reagents, rate constants) are calculated using experimental data. The goal of the inverse problem is to reconstruct of the kinetic scheme of the transformations, i.e., to define the mechanism of the reaction. 

This is connnonly known as the transition state theory approximation to the rate constant. Note that all one needs to do to evaluate (A3.11.187) is to detennine the partition function of the reagents and transition state, which is a problem in statistical mechanics rather than dynamics. This makes transition state theory a very usefiil approach for many applications. However, what is left out are two potentially important effects, tiiimelling and barrier recrossing, bodi of which lead to CRTs that differ from the sum of step frmctions assumed in (A3.11.1831. 

As with the quadmpole ion trap, ions with a particular m/z ratio can be selected and stored in tlie FT-ICR cell by the resonant ejection of all other ions. Once isolated, the ions can be stored for variable periods of time (even hours) and allowed to react with neutral reagents that are introduced into the trapping cell. In this maimer, the products of bi-molecular reactions can be monitored and, if done as a fiinction of trapping time, it is possible to derive rate constants for the reactions [47]. Collision-induced dissociation can also be perfomied in the FT-ICR cell by tlie isolation and subsequent excitation of the cyclotron frequency of the ions. The extra translational kinetic energy of the ion packet results in energetic collisions between the ions and background... 

In the Sharpless epoxidation of divinylmethanols only one of four possible stereoisomers is selectively formed. In this special case the diastereotopic face selectivity of the Shaipless reagent may result in diastereomeric by-products rather than the enantiomeric one, e.g., for the L -(-(-)-DIPT-catalyzed epoxidation of (E)-a-(l-propenyl)cyclohexaneraethanol to [S(S)-, [R(S)-, [S(R)- and [R(R)-trans]-arate constants is 971 19 6 4 (see above S.L. Schreiber, 1987). This effect may strongly enhance the e.e. in addition to the kinetic resolution effect mentioned above, which finally reduces further the amount of the enantiomer formed. 

Analytes A and B react with a common reagent R with first-order kinetics. If 99.9% of A must react before 0.1% of B has reacted, what is the minimum acceptable ratio for their respective rate constants ... 

For both azole and benzazole rings the introduction of further heteroatoms into the ring affects the ease of quaternization. In series with the same number and orientation of heteroatoms, rate constants increase in the order X = 0requires stronger reagents and conditions methyl fluorosulfonate is sometimes used (78AHC(22)71). The 1-or 2-substituted 1,2,3-triazoles are difficult to alkylate, but methyl fluorosulfonate succeeds (7IACS2087). 

First-order and second-order rate constants have different dimensions and cannot be directly compared, so the following interpretation is made. The ratio intra/ inter has the units mole per liter and is the molar concentration of reagent Y in Eq. (7-72) that would be required for the intermolecular reaction to proceed (under pseudo-first-order conditions) as fast as the intramolecular reaction. This ratio is called the effective molarity (EM) thus EM = An example is the nu-... 

Consider a bimolecular reaction between a substrate and a reagent. Upon each encounter of these two species there is a probability P that reaction will occur. If the solution contains two substrates Sj and S2, each characterized by a probability of reaction P, and P2 with the common reagent, evidently the ratio P2lP is a measure of the selectivity of this process for S2 relative to S,. If the two substrates are not markedly dissimilar, the ratio P2IP1 will be similar to the ratio of rate constants, 2/ 1- Leffler and Grunwald pp define the selectivity as... 

As a first approximation, within a given family of nucleophilic reagents, such as amines, basicity changes are mainly responsible for differences in nucleophilic power. The p values of some of the more familiar amines together with the rate constants for some of their reactions with chloroheteroaromatic compounds are shown... 

In addition to the influence of the complexation equilibrium constant K, the observed reaction rate of arenediazonium salts in the presence of guest complexing reagents is influenced by the intrinsic reaction rate of the complexed arenediazonium ion. This system of reactions can be rationalized as in Scheme 11-1. Here we are specifically interested in the numerical value of the intrinsic rate constant k3 of the complexed diazonium ion relative to the rate constant k2 of the free diazonium ion. 

A plot of the first-order rate constant for equilibration in reaction (3-23) is shown as a function of [Co(edta)2 ]. the reagent present in large excess. The plot is linear as expected from Eq. (3-23). Data, from Ref. 1. are given in Table 3-1. 

The rates are essentially independent of the distribution of metal in the MT with similar rates between Zn7—MTm (Cd, Zn)7-MT, and Cd7—MT. The values of the rate constants are ks = 6.9( 0.9) x 10 " s and kf=2.7( 1.2) x 10 s for the holo-protein. The slow rate constant is similar in magnitude to the first-order protein-dependent steps observed for reactions of DTNB (5,5 -dithiobis(2-nitrobenzoate)), EDTA (ethylenediamine tetraacetate), cisplatin, and other reagents, which has been attributed to a rearrangement of the protein. The fast step is more rapid by an order of magnitude, which suggests that other mechanisms are prevailing. 

In order to determine the efficiency of the polymers as reagents in nucleophilic catalysis, it was decided to study the rate of quaternization with benzyl chloride. Table I shows the second-order-rate constants for the benzylation reaction in ethanol. Comparison with DMAP indicates that poly(butadiene-co-pyrrolidinopyridine) is the most reactive of all the polymers examined and is even more reactive than the monomeric model. This enhanced reactivity is probably due to the enhanced hydrophobicity of the polymer chain in the vicinity of the reactive sites. 

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