23.4 Reactions of Aryl Halides: A Review and a Preview TABLE 23.3 Summary of Reactions of Aryl Halides Discussed in Earlier Chapters Reaction(section) and comments General equation and specific example Electrophilic aromatic substitution(Section 12. 14)Halo- gen substituents are slightly deactivating and ortho CHacOCcH CCH3 Formation of aryl Grignard reagents ( Section 14.4) Aryl alides react with magnesium to form the corresponding magnesium halide Aryl iodides are the most reac tive, aryl fluorides the least. A similar reaction occurs Aryl halide Magnesium with lithium to give aryllithium reagents( Section 14.3) Bromobenzene Magnesium Phenylmagnes bromide(95 (a) Hydroxide ion chloromethane (b)Hydroxide ion chlorobenzene FIGURE 23.2 Nucleophilic substitution, with inversion of configuration, is blocked by the benzene ring of an aryl halide. (a) Alkyl halide: the new bond is formed by attack of the nucle ophile at carbon from the side opposite the bond to the leaving group Inversion of configuration is observed. (b)Aryl halide: The aromatic ring blocks the approach of the nucleophile to carbon at the side opposite the bond to the leaving group. Inversion of configuration is impossible Back Forward Main MenuToc Study Guide ToC Student o MHHE Website23.4 Reactions of Aryl Halides: A Review and a Preview 921 TABLE 23.3 Summary of Reactions of Aryl Halides Discussed in Earlier Chapters Reaction (section) and comments Electrophilic aromatic substitution (Section 12.14) Halo￾gen substituents are slightly deactivating and ortho, para-directing. Formation of aryl Grignard reagents (Section 14.4) Aryl halides react with magnesium to form the corresponding arylmagnesium halide. Aryl iodides are the most reac￾tive, aryl fluorides the least. A similar reaction occurs with lithium to give aryllithium reagents (Section 14.3). General equation and specific example Arylmagnesium halide ArMgX Aryl halide ArX Magnesium Mg diethyl ether Bromobenzene Br p-Bromoacetophenone (69–79%) Br CCH3 O CH3COCCH3 AlCl3 O X O X Bromobenzene Br Phenylmagnesium bromide (95%) MgBr Magnesium Mg diethyl ether (a) Hydroxide ion + chloromethane (b) Hydroxide ion + chlorobenzene FIGURE 23.2 Nucleophilic substitution, with inversion of configuration, is blocked by the benzene ring of an aryl halide. (a) Alkyl halide: The new bond is formed by attack of the nucle￾ophile at carbon from the side opposite the bond to the leaving group. Inversion of configuration is observed. (b) Aryl halide: The aromatic ring blocks the approach of the nucleophile to carbon at the side opposite the bond to the leaving group. Inversion of configuration is impossible. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website