Reactions of Nucleophilic Substitutions and Eliminations

Detailed analysis of this reaction mechanism requires a discussion of the electronic structure of both reactants in the framework of the molecular orbital model. We will avoid this approach because it is outside the scope of this book. 

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Additions to quinoline derivatives also continued to be reported last year. Chiral dihydroquinoline-2-nitriles 55 were prepared in up to 91% ee via a catalytic, asymmetric Reissert-type reaction promoted by a Lewis acid-Lewis base bifunctional catalyst. The dihydroquinoline-2-nitrile derivatives can be converted to tetrahydroquinoline-2-carboxylates without any loss of enantiomeric purity <00JA6327>. In addition the cyanomethyl group was introduced selectively at the C2-position of quinoline derivatives by reaction of trimethylsilylacetonitrile with quinolinium methiodides in the presence of CsF <00JOC907>. The reaction of quinolylmethyl and l-(quinolyl)ethylacetates with dimethylmalonate anion in the presence of Pd(0) was reported. Products of nucleophilic substitution and elimination and reduction products were obtained . Pyridoquinolines were prepared in one step from quinolines and 6-substituted quinolines under Friedel-Crafts conditions <00JCS(P1)2898>. 

In this context, an avalanche of studies were devoted to acid-base reactions in their broadest sense (i.e., the Lewis picture), also involving complexation reactions, to the typical organic reactions of addition, substitution, and elimination types, involving nucleophilic and electrophilic reagents including the case of radicalar reactions and excited states (for a review see Ref. [11]) in which our group has... 

Finally, the global and local electrophilicity indexes may be also used to describe the nucleofugality of classical leaving groups in organic chemistry. This potential application incorporates the important families of nucleophilic substitution and elimination reactions. This study is however a bit more complex than the cases presented in this review, because the systematization of nucleofugality within an absolute scale requires an important number of requisites that must be fulfilled, most of them regarding the different reaction mechanisms involved in these complexe reactions. 

Summary This question gives more examples of nucleophilic substitution and elimination reactions ... 

A close look at the nature of a nucleophile will emphasize that it shares common features with a Lewis hase (see Chapter 18). Indeed, a nucleophilic species can act as such a base if the reaction conditions are appropriate - it can remove a proton (H ion) from a halc enoalkane and thereby initiate an elimination reaction. In this type of reaction HX is eliminated from the halogenoalkane and an alkene is produced. It is essential to realize that, given the similarity of the reagents involved, the two processes of nucleophilic substitution and elimination are generally in competition with each other. If a primary halogenoalkane is reacted with aqueous alkali (OH (aq)) then the substitution reaction we have discussed earlier is favoured. However, if ethanolic alkali (OH (ethanol)) is used, then the elimination reaction is favoured. 

In Chapter 9, we introduced the basic principles of nucleophilic substitution and elimination reactions. We focused almost entirely upon the reactions of haloalkanes and alcohols. In this chapter, we will expand upon these reactions and consider a much wider range of nucleophiles, leaving groups, substrates, solvents, and their effects on nucleophilic substitution and elimination reactions. We will ask ... 

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. 

CHAPTER 11 Reactions of Alkyl Halides Nucleophilic Substitutions and Eliminations... 

Chapter 11, Reactions of Alkyl Halides Nucleophilic Substitutions and Eliminations—A discussion of the El cB reaction has been added to Section 11.10, and a new Section 11.11 discusses biological elimination reactions. 

To sum up, primary and secondary substrates generally react by the Sn2 mechanism and tertiary by the SnI mechanism. However, tertiary substrates seldom undergo nucleophilic substitution at all. Elimination is always a possible side reaction of nucleophilic substitutions (wherever a P hydrogen is present), and with tertiary substrates it usually predominates. With a few exceptions, nucleophilic substitutions at a tertiary carbon have little or no preparative value. However, tertiary substrates that can react by the SET mechanism (e.g., /i-N02C6H4CMe2Cl) give very good yields of substitution products when treated with a variety of nucleophiles. ... 

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