The important chemistry of alkyl halides, RX, includes the nucleophilic (SN) displacement and elimination (E) reactions. Recall that tertiary alkyl halides normally are reactive in ionization (SN1) reactions, whereas primary halides, and to a lesser extent secondary halides, are reactive in Sn2 reactions, which occur by a concerted mechanism with inversion of configuration.
Elimination competes with substitution in many SN reactions and can become the major pathway at high temperatures or in the presence of strong base. Elimination (E2), unlike displacement (SN2), is insensitive to steric hindrance in the alkyl halide. In fact, the E2 reactivity of alkyl halides is tert RX > sec RX > prim RX, which is opposite to their SN2 reactivity.
Several useful reactions for the synthesis of alkyl halides that we already have encountered are summarized below with references to the sections that supply more detail:
A summary of these and some other reactions for the synthesis of alkyl halides or organohalogen compounds is given in Table 14-5.
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