Aromatic substitution halogenation

SUBSTITUENT EFFECTS IN ELECTROPHILIC AROMATIC SUBSTITUTION HALOGENS... 

Substituent Effects in Electrophilic Aromatic Substitution Halogens... 

Know the meaning of electrophilic aromatic substitution, halogenation, nitration, sulfonation, alkylation, acylation, Friedel-Crafts reaction. 

Predict products and propose mechanisms for the common electrophilic aromatic substitutions halogenation, nitration, sulfonation, and Friedel-Crafts alkylation and acylation. Problems 17-44, 47, 48, 51, 59, G4, and 70... 

Introduction to Electrophilic Aromatic Substitution Halogenation Sulfonation... 

Rate and Regioselectivity in the Nitration of (Trifluoromethyl)benzene 474 Substituent Effects in Electrophilic Aromatic Substitution Activating Substituents 476 Substituent Effects in Electrophilic Aromatic Substitution Strongly Deactivating Substituents 480 Substituent Effects in Electrophilic Aromatic Substitution Halogens 482 Multiple Substituent Effects 484 Retrosynthetic Analysis and the Synthesis of Substituted Benzenes 486 Substitution in Naphthalene 488 Substitution in Heterocyclic Aromatic Compounds 489... 

Returning to Table 12 2 notice that halogen substituents direct an incoming electrophile to the ortho and para positions but deactivate the ring toward substitution Nitration of chlorobenzene is a typical example of electrophilic aromatic substitution m a halobenzene... 

The two mam methods for the preparation of aryl halides halogenation of arenes by electrophilic aromatic substitution and preparation by way of aryl diazomum salts were described earlier and are reviewed m Table 23 2 A number of aryl halides occur natu rally some of which are shown m Figure 23 1... 

Halogenation (Sections 4 14 and 12 5) Replacement of a hy drogen by a halogen The most frequently encountered ex amples are the free radical halogenation of alkanes and the halogenation of arenes by electrophilic aromatic substitution... 

Many of the common electrophilic aromatic substitution reactions can be conducted on indole. CompHcations normally arise either because of excessive reactivity or the relative instabiUty of the substitution product. This is the case with halogenation. 

The reaction exhibits other characteristics typical of an electrophilic aromatic substitution. Examples of electrophiles that can effect substitution for silicon include protons and the halogens, as well as acyl, nitro, and sulfonyl groups. The feet that these reactions occur very rapidly has made them attractive for situations where substitution must be done under very mild conditions. ... 

I > Br > Cl > F. In nucleophilic aromatic substitution, the formation of the addition intermediate is usually the rate-determining step so the ease of C—X bond breaking does not affeet the rate. When this is the ease, the order of reactivity is often F > Cl > Br > I. This order is the result of the polar effeet of the halogen. The stronger bond dipoles assoeiated with the more eleetronegative halogens favor the addition step and thus inerease the overall rate of reaetion. 

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