Halide as a nucleophile alkyl halides

Halide can be employed as a nucleophile in either Sn2 or SnI reactions to generate an alkyl halide. However, note that, in the general example shown, protonation by the acidic reagent HBr is required to improve the leaving group (see Section 6.1.4). 

The utility of this simple transformation is often to increase the reactivity of the substrate, in that halide is a good leaving group and so can participate in other nucleophilic substitution reactions. 

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