Determining reactions

Halgren T A and Lipscomb W N 1977 The synchronous transit method for determining reaction pathways and locating molecular transition states Chem. Phys. Lett. 49 225... 

Elber R and Karplus M 1987 A method for determining reaction paths in large molecules application to myoglobin Chem. Phys. Lett. 139 375... 

Stachd L L and Ban M I 1992 A global strategy for determining reaction paths Theor. Chim. Acta 83 433... 

Aj ala P Y and H B Schlegel 1997. A Combined Method for Determining Reaction Paths, Minima and Transition State Geometries. Journal of Chemical Physics 107 375-384. 

Elber R and M Karplus 1987. A Method for Determining Reaction Paths in Large Molecules Application to Myoglobin. Chemical Physics Letters 139 375-380. 

In this section we review the application of kinetics to several simple chemical reactions, focusing on how the integrated form of the rate law can be used to determine reaction orders. In addition, we consider how rate laws for more complex systems can be determined. 

These reactions iavolve mostly dimethyl and diethyl sulfate. CycHc sulfates are also reactive, and several have been compared by determining reaction rates with a substituted pyridine or with water (40). In both cases, 1,2-ethylene sulfate is more reactive than 1,3-propylene sulfate or dimethyl or diethyl sulfates. 

Significant advances are being made in the development of effective methods for determining reaction pathways in complex systems. These methods appear to be the most... 

Specific acid catalysis is observed when a reaction proceeds through a protonated intermediate that is in equilibrium with its conjugate base. Because the position of this equilibrium is a function of the concentration of solvated protons, only a single acid-dependent term appears in the kinetic expression. For example, in a two-step reaction involving rate-determining reaction of one reagent with the conjugate acid of a second, the kinetic expression will be as follows ... 

The principal techniques used to determine reaction rate functions from the experimental data are differential and integral methods. 

A reading of Section 2.2 shows that all of the methods for determining reaction order can lead also to estimates of the rate constant, and very commonly the order and rate constant are determined concurrently. However, the integrated rate equations are the most widely used means for rate constant determination. These equations can be solved analytically, graphically, or by least-squares regression analysis. 

The overall direction of the reaction will be determined by the relative concentrations of ATP, ADP, Cr, and CrP and the equilibrium constant for the reaction. The enzyme can be considered to have two sites for substrate (or product) binding an adenine nucleotide site, where ATP or ADP binds, and a creatine site, where Cr or CrP is bound. In such a mechanism, ATP and ADP compete for binding at their unique site, while Cr and CrP compete at the specific Cr-, CrP-binding site. Note that no modified enzyme form (E ), such as an E-PO4 intermediate, appears here. The reaction is characterized by rapid and reversible binary ES complex formation, followed by addition of the remaining substrate, and the rate-determining reaction taking place within the ternary complex. 

A series of pixyl derivatives has been prepared and the half-lives of TFA-induced cleavage determined. Reaction conditions for measurement of the half-lives were TFA, CH2CI2, EtOH, 22°. 

The Synchronous-Transit Method for determining Reaction Pathways and Locating Molecular Transition States Thomas A. Halgren and William N. Lipscomb Chemical Physics Letters 49 (1977) 225-232... 

Kinetics (Section 11.2) Referring to reaction rates. Kinetic measurements are useful for helping to determine reaction mechanisms. 

The characteristics of zero-, first-, and second-order reactions are summarized in Table 11.2. To determine reaction order, the properties in either of the last two columns at the right of the table can be used (Example 11.5). 

The preferred kinetic model for the metathesis of acyclic alkenes is a Langmuir type model, with a rate-determining reaction between two adsorbed (complexed) molecules. For the metathesis of cycloalkenes, the kinetic model of Calderon as depicted in Fig. 4 agrees well with the experimental results. A scheme involving carbene complexes (Fig. 5) is less likely, which is consistent with the conclusion drawn from mechanistic considerations (Section III). However, Calderon s model might also fit the experimental data in the case of acyclic alkenes. If, for instance, the concentration of the dialkene complex is independent of the concentration of free alkene, the reaction will be first order with respect to the alkene. This has in fact been observed (Section IV.C.2) but, within certain limits, a first-order relationship can also be obtained from many hyperbolic models. Moreover, it seems unreasonable to assume that one single kinetic model could represent the experimental results of all systems under consideration. Clearly, further experimental work is needed to arrive at more definite conclusions. Especially, it is necessary to investigate whether conclusions derived for a particular system are valid for all catalyst systems. 

The HMX propints melted in such a manner prior to burning that attempts to determine reaction mechanisms from reaction site observation was not possible... 

The kinetics of desulphonation of sulphonic acid derivatives of m-cresol, mesitylene, phenol, p-cresol, and p-nitrodiphenylamine by hydrochloric or sulphuric acids in 90 % acetic acid were investigated by Baddeley et a/.701, who reported (without giving any details) that rates were independent of the concentration of sulphuric acid and nature of the catalysing anion, and only proportional to the hydrogen ion concentration. The former observation can only be accounted for if the increased concentration of sulphonic acid anion is compensated by removal of protons from the medium to form the undissociated acid this result implies, therefore, that reaction takes place on the anion and the mechanism was envisaged as rapid protonation of the anion (at ring carbon) followed by a rate-determining reaction with a base. 

Pu sulfate complexes for stability constant determination reaction of Pu with diiodoethane. 42-43... 

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