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18: Reactions of Aromatic Compounds

Last updated

Mar 24, 2022
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- 17.11: Solutions to Additional Exercises
- 18.1: Electrophilic Aromatic Substitution (EAS)

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Learning Objectives

After reading this chapter and completing ALL the exercises, a student can be able to

propose mechanisms for Electrophilic Aromatic Substitution Reactions (EAS): halogenation, nitration, sulfonation, and Friedel-Crafts Alkylation & Acylation (sections 18.1 to 18.5)
predict products and specify reagents for Electrophilic Aromatic Substitution Reactions (EAS): halogenation, nitration, sulfonation, and Friedel-Crafts Alkylation & Acylation (sections 18.1 to 18.5)
draw resonance structures of the sigma complexes resulting from EAS rxns of substituted aromatic rings (sections 18.1 to 18.5)
draw reaction energy diagrams for EAS reactions (sections 18.1 to 18.5)
explain why substituents are activating or deactivating and o,p-directors or m-directors (section 18.6)
list the major substituents in their EAS activation “pecking order” (section 18.6)
predict the products of side chain reactions: oxidation of catechols and alkyl substituents, bromination of benzylic carbons, S_N¹ and S_N² rxns at the benzylic carbon, reduction of carbonyls, and reduction of nitro groups (sections 18.7 and 18.12)
design multiple step syntheses that use substituent effects to create the desired isomers of multi-substituted aromatic compounds (sections 18.8 and 18.9)
predict the products of Nucleophilic Aromatic Substitution Reactions (NAS): addition-elimination and elimination-addition (benzyne) (sections 18.10 and 18.11)
propose mechanisms for Nucleophilic Aromatic Substitution Reactions (NAS): addition-elimination and elimination-addition (benzyne) (sections 18.10 and 18.11)

18.1: Electrophilic Aromatic Substitution (EAS)
With six pi electrons, benzene and its derivatives are inherently electrophilic. Electrophilic Aromatic Substitution reactions are a major reaction pathway. One of the benzene hydrogen atoms can be substituted for a different group with electrophilic properties followed by restoration of the stable aromatic ring.
18.2: Halogenation of Benzene (an EAS Reaction)
Halogenation of benzene is an example of electrophillic aromatic substitution. In electrophilic aromatic substitutions, benzene reacts with an electrophile which results in substition of hydrogens. However, halogens are not electrophillic enough to break the aromaticity of benzenes and require a catalyst to activate.
18.3: Nitration of Benzene (an EAS Reaction)
For nitration of benzene, sulfuric acid is used as a catalyst with nitric acid to form the strongly electrophilic nitronium ion.
18.4: Sulfonation of Benzene (an EAS Reaction)
Sulfonation is a reversible reaction that produces benzenesulfonic acid by adding sulfur trioxide and fuming sulfuric acid. The reaction is reversed by adding hot aqueous acid to benzenesulfonic acid to produce benzene.
18.5: Alkylation and Acylation of Benzene - The Friedel-Crafts EAS Reactions
Friedel-Crafts Alkylation and Acylation were first discovered by French scientist Charles Friedel and his partner, American scientist James Crafts, in 1877. These reactions add alkyl groups and acyl groups to benzene rings respectively.
18.6: Substituent Effects on the EAS Reaction
Substituents on benzene rings influence both the rate and location of subsequent Electrophilic Aromatic Substitution (EAS) reactions.
18.7: Side-Chain Reactions of Benzene Derivatives
Side chain reactions can be used to create a wider range of aromatic compounds. This section with focus on three side chain reactions: oxidation of alkyl groups, bromination of alkyl groups, and reduction of acyl groups.
18.8: Synthetic Strategies for Di-substituted Benzenes
To synthesize di-substituted benzene derivatives, the reaction sequence is determined by the directing effects of the substituents.
18.9: Trisubstituted Benzenes - Effects of Multiple Substituents
The regiochemistry of the third substitution on a benzene ring is determined by comparing the effects of the existing substituents. The faster reactivity of activating groups gives them dominance over the slower reacting deactivating groups.
18.10: Nucleophilic Aromatic Substitution - The Addition-Elimantion Mechanism
Although the simple aryl halides are inert to the usual nucleophilic reagents, considerable activation is produced by strongly electron-attracting substituents provided these are located in either the ortho or para positions, or both.
18.11: NAS Reactions - the Elimination-Addition (Benzyne) Mechanism
The elimination-addition mechanism of nucleophilic aromatic substitution involves the remarkable intermediate called benzyne or aryne.
18.12: Reduction of Aromatic Compounds
The reduction reactions of benzene and its derivatives are introduced including the reduction of catechols, nitrobenzenes, and addtional reagents for acyl benzenes.
18.13: Additional Exercises
This section has additional exercises for the key learning objectives of the chapter.
18.14: Solutions to Additional Exercises
This section has the solutions to the additional exercises from the previous section.

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Learning Objectives

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