Give the products, if any, of each of the following...

Give the products, if any, of each of the following reactions: a. benzonitrile $+$ methyl chloride $+\mathrm{AlCl}_{3}$ b. aniline $+3 \mathrm{Br}_{2}$ c. benzoic acid $+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}+\mathrm{AlCl}_{3}$ d. benzene $+2 \mathrm{CH}_{3} \mathrm{Cl}+\mathrm{AlCl}_{3}$

Give the products, if any, of each of the following reactions:
a. benzonitrile $+$ methyl chloride $+\mathrm{AlCl}_{3}$
b. aniline $+3 \mathrm{Br}_{2}$
c. benzoic acid $+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}+\mathrm{AlCl}_{3}$
d. benzene $+2 \mathrm{CH}_{3} \mathrm{Cl}+\mathrm{AlCl}_{3}$

Key Concepts

Limitations Due to Ring Deactivation

In Friedel–Crafts reactions, the presence of strong electron-withdrawing groups on the aromatic substrate can lead to significant deactivation of the ring, thereby preventing the formation of the key arenium ion intermediate. This limitation explains why certain substrates, despite meeting other reaction conditions, may not participate effectively in these alkylation processes.

Substituent Effects on Aromatic Reactivity

The electronic nature of substituents attached to the aromatic ring plays a crucial role in determining both the rate and orientation of electrophilic aromatic substitution reactions. Electron-donating groups (like an amino group) activate the ring and direct incoming electrophiles to the ortho and para positions, while electron-withdrawing groups (such as cyano or carboxylic acid groups) deactivate the ring, often preventing or limiting further reactions under standard conditions.

Electrophilic Halogenation

Electrophilic aromatic halogenation involves the substitution of a hydrogen on the aromatic ring with a halogen atom. In the presence of activating substituents, such as an amino group, the ring becomes much more susceptible to multiple substitutions, often leading to polyhalogenated products. This type of reactivity is exemplified in cases where strong activation results in the formation of compounds like tribrominated aromatics.

Friedel–Crafts Alkylation

This reaction involves the introduction of an alkyl group into an aromatic ring using an alkyl halide and a Lewis acid catalyst such as AlCl3. The process typically proceeds through the generation of a carbocation or a related electrophilic species that attacks the aromatic ring. The reaction’s success is strongly influenced by the nature of the substituents on the aromatic compound, with electron-donating groups generally favoring the reaction and electron-withdrawing groups often hindering it.

Electrophilic Aromatic Substitution

This is a fundamental reaction mechanism for aromatic compounds, where an electrophile replaces a hydrogen atom on the aromatic ring. The overall process involves the formation of a resonance-stabilized arenium ion intermediate, followed by deprotonation to restore aromaticity. Both Friedel–Crafts alkylation and electrophilic bromination are based on this mechanism, with the reactivity and orientation of the substitution being controlled by the ring’s substituents.

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