Chemistry reaction types

Although the pericyclic chemistry of anion radicals has been much slower to emerge than that of cation radicals, the number of intriguing examples now available suggests that this could be an attractive area for future development in electron transfer chemistry. Reaction types which have been exemplified include cyclobutanation, retrocyclobutanation, Diels-Alder addition, electrocyclic reactions, and retroelec-trocyclic reactions. 

Thionyl chloride and phosphorus tribromide are specialized reagents used to bring about particular functional group transformations For this reason we won t present the mechanisms by which they convert alcohols to alkyl halides but instead will limit our selves to those mechanisms that have broad applicability and enhance our knowledge of fundamental principles In those instances you will find that a mechanistic understand mg IS of great help m organizing the reaction types of organic chemistry... 

Section 8 1 Nucleophilic substitution is an important reaction type m synthetic organic chemistry because it is one of the mam methods for functional group transformations Examples of synthetically useful nucleophilic sub stitutions were given m Table 8 1 It is a good idea to return to that table and review its entries now that the details of nucleophilic substitution have been covered... 

In the preceding chapter you learned that nucleophilic addition to the carbonyl group IS one of the fundamental reaction types of organic chemistry In addition to its own reactivity a carbonyl group can affect the chemical properties of aldehydes and ketones m other ways Aldehydes and ketones having at least one hydrogen on a carbon next to the carbonyl are m equilibrium with their enol isomers... 

We 11 see numerous examples of both reaction types m the following sections Keep m mind that m vivo reactions (reactions m living systems) are enzyme catalyzed and occur at far greater rates than those for the same transformations carried out m vitro ( m glass ) m the absence of enzymes In spite of the rapidity with which enzyme catalyzed reactions take place the nature of these transformations is essentially the same as the fundamental processes of organic chemistry described throughout this text... 

Photochemical Reactions. Increased knowledge of the centraUty of quinone chemistry in photosynthesis has stimulated renewed interest in their photochemical behavior. Synthetically interesting work has centered on the 1,4-quinones and the two reaction types most frequentiy observed, ie [2 A 2] cycloaddition and hydrogen abstraction. Excellent reviews of these reactions, along with mechanistic discussion, are available (34,35). 

This chapter presents detailed and thorough studies of chemical synthesis in three quite different chemical systems zinc ferrite, intermetallic, and metal oxide. In addition to different reaction types (oxide-oxide, metal-metal, and metal oxide), the systems have quite different heats of reaction. The oxide-oxide system has no heat of reaction, while the intermetallic has a significant, but modest, heat of reaction. The metal oxide system has a very large heat of reaction. The various observations appear to be consistent with the proposed conceptual models involving configuration, activation, mixing, and heating required to describe the mechanisms of shock-induced solid state chemistry. 

Because the criss-cross cycloaddition reaction is a sequence of two [3+2] cycloaddition steps, the reaction with a,co-diolefins offers a new entry into macro-molecular chemistry New types of polymers with interesting structures and prop erties can be synthesized [213, 214, 215] (equation 48)... 

Alkyl halides are encountered less frequently than their oxygen-containing relatives alcohols and ethers, but some of the kinds of reactions they undergo—nucleophilic substitutions and eliminations—are encountered frequently. Thus, alkyl halide chemistry acts as a relatively simple model for many mechanistically similar but structurally more complex reactions found in biornolecules. We ll begin in this chapter with a look at how to name and prepare alkyl halides, and we ll see several of their reactions. Then in the following chapter, we ll make a detailed study of the substitution and elimination reactions of alkyl halides—two of the most important and well-studied reaction types in organic chemistry. 

Nucleophilic substitution and base-induced elimination are two of the most widely occurring and versatile reaction types in organic chemistry, both in the laboratory and in biological pathways. We ll look at them closely in this chapter to see how they occur, what their characteristics are, and how they can be used. 

Today, we refer to the transformations taking place in Walden s cycle as nucleophilic substitution reactions because each step involves the substitution of one nucleophile (chloride ion, Cl-, or hydroxide ion, HO-) by another. Nucleophilic substitution reactions are one of the most common and versatile reaction types in organic chemistry. 

We said in A Preview ofCnrbonyl Compounds that much of the chemistry of carbonyl compounds can be explained by just four fundamental reaction types nucleophilic additions, nucleophilic acyl substitutions, o substitutions, and carbonyl condensations. Having studied the first two of these reactions in the past three chapters, let s now look in more detail at the third major carbonyl-group process—the a-substitution reaction. 

In 20 years of usage, a,/J-unsaturated Fischer carbene complexes demonstrated their multitalented versatility in organic synthesis, yet new reaction types are still being discovered every year. In view of their facile preparation and multifold reactivity, their versatile chemistry will undoubtedly be further developed and applied in years to come. The application of chirally modified Fischer carbene complexes in asymmetric synthesis has only begun, and it will probably be an important area of research in the near future. 

Chemistry, reaction mechanisms, and properties have been extensively reviewed.4,5,10-20 Hie present chapter deals witii only one type of fully cyclized aromatic heterocyclic polymers die high-molecular-weight linear polymer witii a special emphasis on die synthesis and structure—property relationships for specific applications. 

Metathesis chemistry, histoiy of, 431-432 Metathesis depolymerization, 456-457 Metathesis polymerization, general conditions for, 440-441 Metathesis reactions, types of, 432 Methanol, 377 Methanolysis, 535... 

John D. Corbett once said There are many wonders still to be discovered [4]. This certainly holds generally for all the different areas and niches of early transition cluster chemistry and especially for the mixed-hahde systems. The results reported above so far cover a very Hmited selection of only chloride/iodide systems and basically boron as the interstitial. Because of the very sensitive dependence of the stable stracture built in the soHd-state reaction type on parameters like optimal bonding electron counts, number of cations present, size and type of cations (bonding requirements for the cations), metal/halide ratio, and type of halide, a much larger mixed-hahde cluster chemistry can be expected. Further developments, also in mixed-hahde systems, can be expected by using solution chemistry of molecular clusters, excised from solid-state precursors. 

Abstract The use of A-heterocyclic carbene (NHC) complexes as homogeneous catalysts in addition reactions across carbon-carbon double and triple bonds and carbon-heteroatom double bonds is described. The discussion is focused on the description of the catalytic systems, their current mechanistic understanding and occasionally the relevant organometallic chemistry. The reaction types covered include hydrogenation, transfer hydrogenation, hydrosilylation, hydroboration and diboration, hydroamination, hydrothiolation, hydration, hydroarylation, allylic substitution, addition, chloroesterification and chloroacylation. 

Alkynes have three general reaction types in organic chemistry the reaction of the terminal C-H bond, the reaction of the C-C triple bond, and reactions at the propargyl position and beyond. This chapter mostly describes the first two types of reactions. 

The sulfonium ylide derived chemistry of penicillins continues to meet the interest of several research groups. It is well known that intermolecular carbenoid attack at the sulfur atom generates a sulfonium ylide which undergoes spontaneous opening of the thiazolidine ring to furnish a l,2-sm>-penicillin 326). Novel examples of this reaction type were found upon Rb2(0Ac)4-catalyzed decomposition of diazomalonic esters in the presence of various penicillins this transformation constituted the opening step of a synthetic sequence directed towards 2-alkoxycarbonyl-cephems 345 a) or modified penicillins 345 b). Similar to its reaction with 4-thio-2-azetidinone... 

The interaction between experiment and theory is very important in the field of chemical transformations. In 1981 Kenichi Fukui and Roald Hoffmann received a Nobel Prize for their theoretical work on the electronic basis of reaction mechanisms for a number of important reaction types. Theory has also been influential in guiding experimental work toward demonstrating the mechanisms of one of the simplest classes of reactions, electron transfer (movement of an electron from one place to another). Henry Taube received a Nobel prize in 1983 for his studies of electron transfer in inorganic chemistry, and Rudolf Marcus received a Nobel Prize in 1992 for his theoretical work in this area. The state of development of chemical reaction theory is now sufficiently advanced that it can begin to guide the invention of new transformations by synthetic chemists. 

Apart from this one-reaction type, the routine use of metal template procedures for obtaining a wide range of macrocyclic systems stems from 1960 when Curtis discovered a template reaction for obtaining an isomeric pair of Ni(n) macrocyclic complexes (Curtis, 1960). Details of this reaction are discussed later in this chapter. The template synthesis of these complexes marked the beginning of renewed interest in macrocyclic ligand chemistry which continues to the present day. 

The improvement in the rate of chemical reactions is reversed when temperature is cooler and at temperatures as low as 30 K (a warm comer of TMC-1) the exponential term is of order 10-279 and nearly all reactions between neutral species are frozen out at 50 K. Two important classes of reactions survive radical-radical chemistry and ion-molecule chemistry. The importance of these different reaction types will become apparent later with the construction of the models of molecular clouds. For the moment, however, laboratory measurements of reactions in radicals such as C2H have shown that even with temperatures as low as 15 K the rate constant for reactions of the type ... 

High performance sealants, 22 28 High phosphorus alloys, corrosion performance of, 9 710-711 High pinning Type II superconductors, 23 High pressure apparatus, 13 413 High pressure applications, 13 436-448 in commercial products, 13 436-438 in inorganic chemistry reactions, 13 440—448... 

---