Mechanistic kinetics

TFA. Electrophilic aromatic thallation with TTFA therefore constitutes a simple and general procedure for the preparation of monoarylthallium(III) derivatives and has been the subject of detailed kinetic, mechanistic, and synthetic investigations. These aspects of the thallation reaction are discussed at length below. 

Following the adoption of azolides as valuable and versatile reagents in synthetic organic chemistry,[1] and also in the context of their potential role in biochemistry, a great many kinetic, mechanistic, and theoretical papers appeared concerning this group of compounds and their properties. Some of these papers[18],[20] are very useful for a better understanding of the reactivity of azolides. 

Those currently actively involved in anionic polymerization will recognize that despite the extensive progress that has been made over the past 25 years, many kinetic, mechanistic, and even synthetic aspects have not been elucidated fully. Thus, it should not be surprising that there are opposing points of view. In the past, controversies have occurred, and although I tried to minimize this factor, I was not completely successful in this regard. However, I was pleased that all of the speakers came to the same room and also contributed to this volume. A few of the papers may be a bit strong however, I have decided to let the scientific community come to their own decisions on these matters. 

Kinetic-Mechanistic Aspects of Polymerisation with Ziegler-Natta Catalysts... 

The extreme importance of both the thermodynamic (free energy) and kinetic (mechanistic pathway) considerations makes it necessary to analyse these factors more thoroughly and from other perspectives. 

Z. Lm and T. J. Marks, J. Am. Chem. Soc., 112, 5515 (1990). A Kinetic Mechanistic, and Molecular Mechanics Investigation of Olefin Insettion into Organoactinide-Hydride Bonds. Metal, Olefin, Ancillary Ligand, and Diastereoselection Effects. 

The most useful sources of atomic sulfur for kinetic-mechanistic studies presently described in the literature are all photolytic. Some interesting studies, however, have also been reported on the production of recoil sulfur atoms from nuclear reactions. 

In almost all of the gas-phase kinetic-mechanistic studies on sulfur atom reactions made to date, the source has been the in situ photolysis of carbonyl sulfide (COS). The reasons for this choice are not far to seek. Carbonyl sulfide is a stable, readily available gas. Its absorption spectrum is located in a convenient spectral region and the carbon monoxide formed in the photodissociation provides an excellent internal monitor for sulfur atom production. 

Investigation of the Origins of Selectivity in Ethylene Epoxidation on Promoted and Unpromoted Ag/a-Al2O3 Catalysts A Detailed Kinetic, Mechanistic and Adsorptive Study... 

A major point was made after a critical review of numerous reports on reaction rates in frozen systems (50). Kinetic-mechanistic surprises in frozen systems may not require exceptional hypotheses. Concentration effects may account for them. Even if a system appears to be completely solidified and, therefore, not amenable to analysis in terms of unfrozen liquid puddles (51), a liquid phase should still be considered a possibility. A case in point is provided by the efficient electron transfer observed between ferrous and ferric ions in an aqueous system frozen below its putative eutectic point (52). This seemed to require an ice structure in order to bridge the distance between reactants that were calculated to be too far apart for significant reactivity. However, it was pointed out that the assumed eutectic point was based only on the major... 

Unfortunately for the individual investigator, it appears that the way to progress in this field is through complicated preparation methods, the use of heavy techniques such as TEM and EXAFS, and detailed kinetic (mechanistic) studies on each catalyst. Ideally, single-crystal and metal cluster studies would be done on the same systems. The holders of purse strings will have to decide whether the added understanding resulting from these expensive studies is justified in a field in which empiricism has... 

The examples presented in this chapter also illustrate a development of the structure correlation method itself. Initially, it was applied to whatever representatives of a specific fragment happened to be available (Cd). Later, directed searches in the CSD [6] led to sometimes surprising new types of correlations (Sn). More recently, compounds have been synthesized in a planned way and their structures determined, so that a specific structural feature or reactivity problem could be studied (Si, B). We have also seen that the methods and interpretations of structure correlation can be applied to results of quantum-chemical calculations. Combinations of kinetic, mechanistic, and computational studies together with structure correlations, are just beginning to illuminate as yet poorly understood problems of chemical reactivity and selectivity, e.g. the factors differentiating between substitutions proceeding with retention or inversion at Si. 

Let us first consider briefly how the use of mass transport as a variable can provide a guide to the reaction mechanism and give quantitative kinetic detail. As an illustration, we consider the behaviour of CE and EC processes (where E signifies electron transfer and C represents a chemical step) at a rotating disc electrode (RDE). This hydrodynamic system has already been discussed by Albery et al. and the reader is referred to Chap. 4 for details. CE and EC processes represent the simplest conceivable electrode reactions involving coupled homogeneous kinetics mechanistic examples of both types are shown in Table 1. In the discussion which follows, the electron-transfer reaction in the two mechanisms is considered to be a cathodic process the extension to the anodic case is trivial. 

Hydroxy-l,2-benziodoxole-3(l//)-one (104) is commercially available or can be easily prepared by direct oxidation of 2-iodobenzoic acid or by basic hydrolysis of 2-(dichloroiodo)benzoic acid [232,233,274]. A more recent preparative procedure for 104 involves the oxidation of 2-iodobenzoic acid with acetyl nitrate in acetic anhydride at room temperature followed by aqueous work-up [275]. In the 1980s benziodoxole 104 and other hydroxybenziodoxoles attracted considerable research interest due to their excellent catalytic activity in the cleavage of toxic phosphates and reactive esters. This activity is explained by a pronounced O-nucleophilicity of the benziodoxole anion 105 due to the a-effect [234,272,276]. Spectroscopic and kinetic mechanistic studies indicate that the highly unstable iodoxole derivatives, such as the phosphate 107, are reactive intermediates in catalytic cleavage of phosphates, as shown for the catalytic hydrolysis of a typical substrate 106 (Scheme 2.39) [277-279]. This mechanism was proved by the synthesis and reactivity studies of the phosphate intermediate 107. 

Many authors have used the acronym ALS to refer to the enzyme that catalyzes the reaction of Fig. 2.1.1. However, since ALS refers specifically to the pathway leading to valine and leudne through the intermediate (S)-2-acetolactate, the designation AHAS better describes all products of the reaction. AHAS is present in bacteria, fungi, and plants. Many of the early kinetic, mechanistic, and structural studies were carried out with AHAS isolated and purified from enteric bacteria such as Escherichia coli and Salmonella typhimurium. Eukaryotic AHAS has proven more difficult to isolate and purify because of its reduced stability. Three AHAS isozymes have been characterized in bacteria - AHAS I, II, and III - whereas only one isozyme is known in fungi and plants. 

Electrochemical methods have diverse applications in chemistry - synthesis, catalysis, thermodynamics, kinetics, mechanistic studies, to mention a few. Electrochemistry was well developed for studies of relevance to organometallic chemistry prior to COMC (1995), but there was no separate section devoted to the topic in that work. However, excellent books and reviews have been published that summarize aspects of organometallic electrochemistry. 

Roncaroli F, Ruggiero ME et al (2002) Kinetic, mechanistic, and DFT study of the electrophilic reactions of nitrosyl complexes with hydroxide. Inorg Chem 41 5760-5769... 

The M—(NO ) and M—(HNO) (M = Fe, Ru) complexes described in this work have been shown to be reactive under an oxygen atmosphere, either in nonaqueous or aqueous media, though no kinetic/mechanistic studies are available (13—15). Once the speciation of the NO /HNO complexes is known, there is an obvious need to make advances in the studies on this type of reactivity, particularly in biorelevant aqueous media, with a need of disclosing the similarities and differences with autoxidation reactions of = 7 complexes, like those described in Section 3.4 for [Fe(CN)sNO] and other related nonheme and heme-lMXsNO ions. 

Our work during the project is part of a concerted effort of various European groups to unravel the mechanism of tropospheric oxidation of aromatics. A lot of kinetic, mechanistic and analytic data have been produced, especially concerning (i) the first primary steps of the mechanism (abstraction and addition) (ii) the nature and the yield of intermediate or final oxidation products. Also, it appeared that "standard" reaction schemes for oxidation (Le. like those for alkanes) are not applicable to aromatics this specificity of the latter prevented us from presenting a clear picture of the oxidation mechanism and requires new investigations. 

A kinetic-mechanistic investigation of the reactions of CF3 with CF3, F and O2 and of CF3O2, /-C3H7O2, and J-C4H9O2 with NO,... 

Du Y.J., Lemstra R.J., Nijenhuis A.J., Van Aert H.A.M., Bastiaansen C., ABA type copolymers of lactide with poly(ethylene glycol). Kinetic, mechanistic, and model studies. Macromolecules, 28(7), 1995, 2124-2132. 

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