ELECTROPHILIC AROMATIC SUBSTITUTION …

762 CHAPTER 16 THE CHEMISTRY OF BENZENE AND ITS Show two different Friedel Crafts acylation reactions that can be used to prepare the follow-ing following compound reacts with AlCl3followed by water to give a ketone Awith the for-mula C10H10O. Give the structure of Aand a curved-arrow mechanism for its AROMATIC SUBSTITUTION reactions OF SUBSTITUTED BENZENESA. Directing Effects of SubstituentsWhen a monosubstituted benzene undergoes an ELECTROPHILIC AROMATIC SUBSTITUTION reaction,three possible disubstitution products might be obtained. For example, nitration of bromoben-zene could in principle giveortho-,meta-,orpara-bromonitrobenzen e. If SUBSTITUTION weretotally random, an ortho : meta : para product ratio of 2 : 2 : 1 would be expected. (Why?) It isfound experimentally that this SUBSTITUTION isnotrandom, but ELECTROPHILIC SUBSTITUTION reactions of bromobenzene also give mostly ortho and paraisomers. If a substituted benzene undergoes further SUBSTITUTION mostly at the ortho and parapositions, the original substituent is called an ortho, para-directing , bromine isan ortho, para-directing group, because all ELECTROPHILIC SUBSTITUTION reactions of bromoben-zene occur at the ortho and para contrast, some substituted benzenes react in ELECTROPHILIC AROMATIC SUBSTITUTION to givemostly the meta disubstitution product.

16.5 ELECTROPHILIC AROMATIC SUBSTITUTION REACTIONS OF SUBSTITUTED BENZENES 763 nal substituent group is called a meta-directing group. Thus, the nitro group is a meta-directing group because all electrophilic substitution reactions of nitrobenzene occur at the

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  Aromatic, Reactions, Substitution, Electrophilic aromatic substitution, Electrophilic, Electrophilic aromatic substitution reactions of

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