Examples of Complex Reactions

Two factors are responsible for the sequence of elementary processes common for all complex radiation-chemical reactions the relatively low rate of active species generation at typical dose rates and the high rate constant of ionmole-cule reactions. As a result, the sequence of the majority of conceivable ionic processes must include  

This sequence has been formulated recently and independently by several authors [467, 457] departing from the high rates of ion-molecule reactions. 

Indeed, equating the rate of ion formation under continuous irradiation to the rate of their neutralization in the gas 

On the other hand, the characteristic time of the reaction of an ion with a molecular compound of concentration nM = 10 cm (with the typical rate constant value 10-10 cm s) is 

the primary ion succeeds in converting, before neutralization, to a second generation ion. Moreover, if there are additionally exotherniic or thermoneutral conversion 

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In certain cases, a single-step electrochemical process can be derived out of a complex sequence of reactions. The electrolysis proposed by Ziegler35 and Lehmkuhl36, in which sodium tetramethylaluminate is electrolyzed between a lead anode and mercury in THF, is an example of complex reactions of very sensitive compounds which are translated into a simplified electrolytic procedure ... 

In practice, reaction orders can be fractional, indicating a complex reaction mechanism. The majority of this book is devoted to such cases, as catalytic reaction mechanisms, which follow from the general considerations above, are typical examples of complex reactions. 

An important example of complex reactions are those involving/ree radicak in chain reactions. These reactions consist of three essential steps ... 

Catalytic processes provide excellent examples of complex reactions. The catalyst is viewed as combining with some of the reactants to form an intermediate species which subsequently reacts to form products with the return of the c yst to its original state so that it can continue to further participate in the reaction. Scientists and physical chemists have concluded that the catalyzed path requires a lower activation energy and thus can proceed more rapidly. 

As this is written, there are undoubtedly more examples of complex reactions being developed in laboratories around the world. An understanding of how fluid motion and particularly, turbulence can affect the path of reactions is extremely... 

In a simple liquid-liquid extraction the solute is partitioned between two immiscible phases. In most cases one of the phases is aqueous, and the other phase is an organic solvent such as diethyl ether or chloroform. Because the phases are immiscible, they form two layers, with the denser phase on the bottom. The solute is initially present in one phase, but after extraction it is present in both phases. The efficiency of a liquid-liquid extraction is determined by the equilibrium constant for the solute s partitioning between the two phases. Extraction efficiency is also influenced by any secondary reactions involving the solute. Examples of secondary reactions include acid-base and complexation equilibria. 

Considering the attention that we have given in this chapter to concentrationtime curves of complex reactions, it may seem remarkable that many kinetic studies never generate a comprehensive set of complicated concentration-time data. The reason for this is that complex reactions often can be studied under simplified conditions constituting important special cases for example, whenever feasible one chooses pseudo-first-order conditions, and then one studies the dependence of the pseudo-first-order rate constant on variables other than time. This approach is amplified below. 

The net reaction catalyzed by this enzyme depends upon coupling between the two reactions shown in Equations (3.26) and (3.27) to produce the net reaction shown in Equation (3.28) with a net negative AG°. Many other examples of coupled reactions are considered in our discussions of intermediary metabolism (Part III). In addition, many of the complex biochemical systems discussed in the later chapters of this text involve reactions and processes with positive AG° values that are driven forward by coupling to reactions with a negative AG°. ... 

Gases, fluids, crystals, and lasers are all examples of complex systems that are familiar to ns from physics. Chemical reactions, in which a large number of molecules conspire to produce new molecules, are also good examples. From biology, we have DNA molecules built up from amino acids, cells built from molecules, and organisms built from colls. 

Some more complex examples of this reaction type from the field of natural product synthesis, using a ketone, a thioenol ether, or a phenyl function as an internal nucleophile, are found in references 171-173. 

An example of a reaction series in which large deviations are shown by — R para-substituents is provided by the rate constants for the solvolysis of substituted t-cumyl chlorides, ArCMe2Cl54. This reaction follows an SN1 mechanism, with intermediate formation of the cation ArCMe2 +. A —R para-substituent such as OMe may stabilize the activated complex, which resembles the carbocation-chloride ion pair, through delocalization involving structure 21. Such delocalization will clearly be more pronounced than in the species involved in the ionization of p-methoxybenzoic acid, which has a reaction center of feeble + R type (22). The effective a value for p-OMe in the solvolysis of t-cumyl chloride is thus — 0.78, compared with the value of — 0.27 based on the ionization of benzoic acids. 

Palladium(II) complexes provide convenient access into this class of catalysts. Some examples of complexes which have been found to be successful catalysts are shown in Scheme 11. They were able to get reasonable turnover numbers in the Heck reaction of aryl bromides and even aryl chlorides [22,190-195]. Mechanistic studies concentrated on the Heck reaction [195] or separated steps like the oxidative addition and reductive elimination [196-199]. Computational studies by DFT calculations indicated that the mechanism for NHC complexes is most likely the same as that for phosphine ligands [169], but also in this case there is a need for more data before a definitive answer can be given on the mechanism. 

Recently the first examples of complexes between the four-membered amidinato-Group 13 metal(l) heterocycles and transition metal fragments were reported. Complexes of the type CpFe(CO)2[M(X) But(NR)2 ] (M = Al, Ga, In X = Cl, Br R = Pri, Gy) were formed in salt-elimination reactions between Na[CpFe(CO)2] and [But(NR)2]MX2. A series of complexes between the four-membered amidinato-Group 13 metal(l) heterocycles and Group 10 metal(O) fragments have been prepared according to Scheme 35. ... 

Another difference between the two mechanisms is that the former involves 1,2 and the latter 1,3 shifts. The isomerization of 1-butene by rhodium(I) is an example of a reaction that takes place by the metal hydride mechanism, while an example of the TT-allyl complex mechanism is found in the Fe3(CO)i2 catalyzed isomerization of 3-ethyl-l-pentene. " A palladium acetate or palladium complex catalyst was used to convert alkynones RCOCSCCH2CH2R to 2,4-alkadien-l-ones RCOCH= CHCH = CHCHR. ... 

During a study of these complexes, Treichel and Hess 145, 147) heated [Pt(PPh3)2(CNCH3)Cl]Cl, expecting to obtain Pt(PPh3)(CNCHj)Cl2 instead a novel dealkylation reaction occurred. This was extended to other related species [Eq. (36)]. Remarkably, very few examples of such reactions... 

Abstract In general, asymmetric catalysts are based on the combination of a chiral organic ligand and a metal ion. Here we show that future research should also focus on complexes in which the chirality resides only at the metal center, as the result of a given topology of coordination of achiral ligands to the metal ion. Here we make a brief presentation of the methods available for preparing such compounds as well as the very few examples of enantioselective reactions catalyzed by chiral-at-metal complexes. 

Antibody molecules are bivalent whilst antigens can be multivalent. The resultant combination may result in either small, soluble complexes, or large insoluble aggre tes, depending on the nature of the two molecules in the system. The following are examples of the reactions that can occur. 

The focus of Part B is on the closely interrelated topics of reactions and synthesis. In each of the first twelve chapters, we consider a group of related reactions that have been chosen for discussion primarily on the basis of their usefulness in synthesis. For each reaction we present an outline of the mechanism, its regio- and stereochemical characteristics, and information on typical reaction conditions. For the more commonly used reactions, the schemes contain several examples, which may include examples of the reaction in relatively simple molecules and in more complex structures. The goal of these chapters is to develop a fundamental base of knowledge about organic reactions in the context of synthesis. We want to be able to answer questions such as What transformation does a reaction achieve What is the mechanism of the reaction What reagents and reaction conditions are typically used What substances can catalyze the reaction How sensitive is the reaction to other functional groups and the steric environment What factors control the stereoselectivity of the reaction Under what conditions is the reaction enantioselective ... 

There are relatively few examples of the reaction of platinum(O) with tertiary silanes. A novel example is the reaction of [Pt(PEt3)4] with the rhodium complex [RhCl(H)(SiAr3)(P(Pr1)3)2], which results in silane transfer to give the platinum(II) complex cis- [PtHtSiArsXPCPr1) ].64... 

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