General and Mechanistic Aspects

The steam cracker process - sometimes in the literature also referred to as middle temperature pyrolysis process - forms the heart of modern petrochemistry. The process converts a crude oil distillation cut into a mixture of reactive small molecules that can be purified and later used to produce a wide variety of base chemicals. It is fair to state that modem petrochemistry has developed around the steam cracker process and operates today largely as a result of the characteristic product distribution provided by the steam cracker. 

2) As the mixture of cracking products is composed partly of highly reactive small alkenes, it is very important to prevent polymerization or reaction of these products in the cracking oven. The probability of these undesired side reactions forming polymer or coke is significantly reduced in the presence of steam. 

Owing to these thermodynamic facts, equilibrium conversions have to be avoided in the steam cracking process as under all technically realistic conditions the desired products (light alkenes, aromatics) are thermodynamically unstable. Thus, reaching the equilibrium in a steam cracker would mean that most of the valuable 

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Of organic As, Sb and Bi compounds, the electrochemistry of organic As compounds has been most explored, the electrochemistry of organic Sb compounds to a lesser extent and the electrochemistry of Bi compounds only very little. Much of the electrochemical work on organic As compounds has been carried out in aqueous solution for analytical purposes due to the earlier widespread industrial applications of organic As compounds and their toxicity to humans. However, the analytical aspects of some of the studies have been reviewed previously and will not be treated here, but the general and mechanistic aspects of these studies are included. 

Synthetic and mechanistic aspects of iatramolecular cycli2ation in the tricycHc diterpenoid area have been studied in detail. In general, the presence of electron withdrawing groups such as carbonyl in the side chain retard the rates of cycli2ation (61). 

This theory proves to be remarkably useful in rationalizing the whole set of general rules and mechanistic aspects described in the previous section as characteristic features of the Diels-Alder reaction. The application of perturbation molecular orbital theory as an approximate quantum mechanical method forms the theoretical basis of Fukui s FMO theory. Perturbation theory predicts a net stabilization for the intermolecular interaction between a diene and a dienophile as a consequence of the interaction of an occupied molecular orbital of one reaction partner with an unoccupied molecular orbital of the other reaction partner. 

The book is arranged in 14 chapters. After discussing general aspects, separation of hydrocarbons from natural sources and synthesis from Ci precursors with the most recent developments for possible future applications, each chapter deals with a specific type of transformation of hydrocarbons. Involved fundamental chemistry, including reactivity and selectivity, as well as stereochemical considerations and mechanistic aspects are discussed, as are practical applications. In view of the immense literature, the coverage cannot be comprehensive and is therefore selective, reflecting the authors own experience in the field. It was attempted nevertheless to cover all major aspects with references generally until the early 1994. 

The section on catalyst preparation (Chapters 8 and 9) is concerned with the preparation of catalyst supports, zeolites, and supported catalysts, with an emphasis on general principles and mechanistic aspects. For the supported catalysts the relation between the preparative method and the surface chemistry of the support is highlighted. The molecular approach is maintained throughout. 

The kinetic and mechanistic aspects of this general area tend to be strongly dependent on the particular system. This makes general treatments and explanations impossible, at least at the current stage of understanding. Various aspects of this area have been summarized in some general reviews. 

A book surveys the catalysis of industrially significant reactions and another the chemistry of metal carbene complexes with reference to their intermediacy in catalytic reactions. General discussions of transition metal catalysed processes have appeared " , and mechanistic aspects of the literature covering the period mid-1982 to end-1983 have been reviewed. ... 

Ivin, K. J., and Saegusa, T., (1984). General Thermodynamic and Mechanistic Aspects of Ring-opening Polymerization . In Ring-Opening Polymerization (Ivin, K. J., and Saegusa, T., eds.), Elsevier Applied Science Publishers, London/New York, pp. 1. 

Some limitations of the subject surveyed have been necessary in order to keep the size of the chapter within the reasonable bounds. Accordingly, to make it not too long and readable, the discussion of the methods of the sulphoxide synthesis will be divided into three parts. In the first part, all the general methods of the synthesis of sulphoxides will be briefly presented. In the second one, methods for the preparation of optically active sulphoxides will be discussed. The last part will include the synthetic procedures leading to functionalized sulphoxides starting from simple dialkyl or arylalkyl sulphoxides. In this part, however, the synthesis of achiral, racemic and optically active sulphoxides will be treated together. Each section and subsection includes, where possible, some considerations of mechanistic aspects as well as short comments on the scope and limitations of the particular reaction under discussion. 

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