Reactivity Basic Principles

The reaction of an alcohol with a hydrogen halide is a substitution A halogen usually chlorine or bromine replaces a hydroxyl group as a substituent on carbon Calling the reaction a substitution tells us the relationship between the organic reactant and its prod uct but does not reveal the mechanism In developing a mechanistic picture for a par ticular reaction we combine some basic principles of chemical reactivity with experi mental observations to deduce the most likely sequence of steps... 

In order to establish the conditions for thermodynamic feasibility of reactive mass exchange, it is necessary to invoke the basic principles of mass transfer with chemical reactions. Consider a lean phase j that contains a set Bj = z —... 

After a decade of research the basic principles in the chemistry of decamethylsilicocene (1) seem to be understood. This compound shows the reactivity of a nucleophilic silylene due to the fact that the Tt-bonded pentamethylcyclopentadienyl ligands are easily transferred to a-bonded substituents during the reaction. The steric requirements of these substituents permit reactions with bulky substrates. The migratory aptitude and the leaving-group character of the pentamethylcyclopentadienyl groups... 

The roles of carbocations in commercially important hydrocarbon transformations are still not perfectly understood. The same can be said for carbocations in biological systems. Significant questions concerning reactivity still need to be explained. Why do so many reactions of carbocations show constant selectivity, in violation of the reactivity-selectivity principle Is it possible to develop a unified scale of elec-trophilicity-nucleophilicity, in particular one that incorporates these parameters into the general framework of Lewis acidity and basicity. Finally, quite sophisticated synthetic transformations are being developed that employ carbocations, based upon insights revealed by the mechanistic studies. 

The basic principles governing the degree and type of reactivity shown by heteroaromatic compounds are familiar from aliphatic and benzenoid chemistry. Three are very important ... 

This article will illustrate several methods by which back electron transfer can be obviated and hence by which organic transformations can be accomplished. Because this field has been so active, a comprehensive review of all work accomplished toward these objectives would be impossible. The coverage of this article is therefore restricted to recent, rather arbitrarily chosen, experiments which exemplify the basic principles governing both electron exchange between excited organic molecules and appropriate redox partners and the subsequent chemical reactivity of the reduced and oxidized species formed in the photochemical step. 

This chapter begins with an introduction to the basic principles that are required to apply radical reactions in synthesis, with references to more detailed treatments. After a discussion of the effect of substituents on the rates of radical addition reactions, a new method to notate radical reactions in retrosynthetic analysis will be introduced. A summary of synthetically useful radical addition reactions will then follow. Emphasis will be placed on how the selection of an available method, either chain or non-chain, may affect the outcome of an addition reaction. The addition reactions of carbon radicals to multiple bonds and aromatic rings will be the major focus of the presentation, with a shorter section on the addition reactions of heteroatom-centered radicals. Intramolecular addition reactions, that is radical cyclizations, will be covered in the following chapter with a similar organizational pattern. This second chapter will also cover the use of sequential radical reactions. Reactions of diradicals (and related reactive intermediates) will not be discussed in either chapter. Photochemical [2 + 2] cycloadditions are covered in Volume 5, Chapter 3.1 and diyl cycloadditions are covered in Volume 5, Chapter 3.1. Related functional group transformations of radicals (that do not involve ir-bond additions) are treated in Volume 8, Chapter 4.2. 

The purpose of this chapter is to provide an introduction to the scope and limitations of radical cyclization reactions. Emphasis will be placed on the reactivity profile of radicals with respect to chemo-, regio-and stereo-selectivity. Because most sequential radical reactions include at least one cyclization, they are also presented in this chapter. The organization of this chapter is similar to the previous chapter on radical additions. However, the basic principles of radical reactions, selectivity requirements, methods to conduct radical reactions (including experimental techniques), and mechanisms are extensively discussed in the previous chapter, and these aspects will be reiterated rather sparingly. A reader who is not familiar with the principles of radical reactions as applied to synthesis should read the addition chapter (Chapter 4.1, this volume) first. 

The basic principle behind etching a solid material with a reactive gas discharge is inherently simple. A gas is chosen that dissociates into reactive... 

Mechanisms, of proton transfer between oxygen and nitrogen acids and bases in aqueous solutions, 22, 113 Mechanisms, organic reaction, isotopes and, 2, 1 Mechanisms of reaction, in solution, entropies of activation and, 1, 1 Mechanisms of reaction, of /3-lactam antibiotics, 23, 165 Mechanisms of solvolytic reactions, medium effects on the rates and, 14, 10 Mechanistic analysis, perspectives in modern voltammeter basic concepts and, 32, 1 Mechanistic applications of the reactivity-selectivity principle, 14, 69 Mechanistic studies, heat capacities of activation and their use, 5, 121 Mechanistic studies on enzyme-catalyzed phosphoryl transfer, 40, 49 Medium effects on the rates and mechanisms of solvolytic reactions, 14, 1 Meisenheimer complexes, 7, 211... 

Chapter 3. Basic Principles of Organic Ion Radical Reactivity... 

Ruchardt C (1987) Basic principles of reactivity in free radical chemistry. Free Radical Res Commun 2 197-216... 

Relationships of molecular topology to chemical reactivity of polynuclear benzenoid hydrocarbons are of interest for both theoreticians and experimentalists. Reactivity indices, derived from topological approaches to the chemistry of benzenoid hydrocarbons, have proved useful in such varied fields as mechanistic organic chemistry, biochemistry, carbon science, and environmental science. It is not the aim of this review, however, to give a comprehensive account of reactivity indices of benzenoid hydrocarbons. Instead, the main emphasis is placed on the underlying basic principles of the relationship between topology and reactivity of benzenoid hydrocarbons. 

This book does not follow a chronological sequence but rather builds up in a hierarchy of complexity. Some basic principles of 51V NMR spectroscopy are discussed this is followed by a description of the self-condensation reactions of vanadate itself. The reactions with simple monodentate ligands are then described, and this proceeds to more complicated systems such as diols, -hydroxy acids, amino acids, peptides, and so on. Aspects of this sequence are later revisited but with interest now directed toward the influence of ligand electronic properties on coordination and reactivity. The influences of ligands, particularly those of hydrogen peroxide and hydroxyl amine, on heteroligand reactivity are compared and contrasted. There is a brief discussion of the vanadium-dependent haloperoxidases and model systems. There is also some discussion of vanadium in the environment and of some technological applications. Because vanadium pollution is inextricably linked to vanadium(V) chemistry, some discussion of vanadium as a pollutant is provided. This book provides only a very brief discussion of vanadium oxidation states other than V(V) and also does not discuss vanadium redox activity, except in a peripheral manner where required. It does, however, briefly cover the catalytic reactions of peroxovanadates and haloperoxidases model compounds. 

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