Nucleophiles halides

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. 

First order Rate = k[alkyl halide] (Section 8 8) Second order Rate = k[alkyl halide][nucleophile] (Section 8 3)... 

Section 10 10 Protonation at the terminal carbon of a conjugated diene system gives an allylic carbocation that can be captured by the halide nucleophile at either of the two sites that share the positive charge Nucleophilic attack at the carbon adjacent to the one that is protonated gives the product of direct addition (1 2 addition) Capture at the other site gives the product of conjugate addition (1 4 addition)... 

Kinetic studies of these reactions reveal that they follow a second order rate law Rate = [Aryl halide] [Nucleophile]... 

Attack by the halide nucleophile at the sp hybridized carbon of the alkyl group is anal ogous to what takes place in the cleavage of dialkyl ethers Attack at the sp hybridized carbon of the aromatic nng is much slower Indeed nucleophilic aromatic substitution does not occur at all under these conditions... 

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. 

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