Alkylation Reactions Nucleophilic Substitution

A C5 isoprene unit in the form of dimethylallyl diphosphate (DMAPP) may also act as an 

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These reactions follow first-order kinetics and proceed with racemisalion if the reaction site is an optically active centre. For alkyl halides nucleophilic substitution proceeds easily primary halides favour Sn2 mechanisms and tertiary halides favour S 1 mechanisms. Aryl halides undergo nucleophilic substitution with difficulty and sometimes involve aryne intermediates. 

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. 

Ionic Reactions—Nucleophilic Substitution and Elimination Reactions of Alkyl Halides... 

The basic hydrolysis (reaction with water) of a nitrile (R-CN) followed by acidification yields a carboxylic acid. In general, an reaction (nucleophilic substitution) of an alkyl halide is used to generate the nitrile before hydrolysis. Figure 12-12 illustrates the formation of a carboxylic acid beginning with an alkyl halide. 

One equivalent of NaOEt in EtOH deprotonates diethyl malonate completely to give the sodium enolate A (Figure 13.36). This enolate is monoalkylated upon addition of an alkylating reagent such as BuBr, and a substituted malonic ester C is formed. During the alkylation reaction, the substituted malonic ester C reacts to a certain extent with some of the enolate A, resulting in the butylated enolate B and unsubstituted neutral malonic ester. It is for this reason that the reaction mixture contains two nucleophiles—the original enolate A and the butylated enolate B. The alkylation of A with butyl bromide is much faster than that of B, since A is less sterically hindered than B. The main product is therefore the product of monoalkylation. Distillation can be used to separate the main product from small amounts of the product of dialkylation. 

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