chapter 8 aromaticity reactions of benzene and substituted benzenes 1

Chapter 8

Aromaticity

Reactions of Benzene and

Substituted Benzenes

1

The first structure for benzene was

proposed by August Kekulé in 1872.

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3

We often represent benzene as a hybrid of two equivalent structures

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To name a benzene ring with one substituent, name the substituent and add the word benzene.

Naming Benzene Compounds

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Common Names

OMe CH3 OH NH2

anisole toluene phenol aniline

CHO COOH CNstyrene benzaldehyde benzoic acid benzonitrile

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ortho-dibromobenzene

or

o-dibromobenzene

or 1,2-dibromobenzene

meta-dibromobenzene

or

m-dibromobenzene

or 1,3-dibromobenzene

para-dibromobenzene

or

p-dibromobenzene

or 1,4-dibromobenzene

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• If the two groups on the benzene ring are different, alphabetize the names of the substituents preceding the word benzene.

• If one substituent is part of a common root, name the molecule as a derivative of that monosubstituted benzene.

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For three or more substituents on a benzene ring:

1. Number to give the lowest possible numbers around the ring.

2. Alphabetize the substituent names.

3. When substituents are part of common roots, name the molecule as a derivative of that monosubstituted benzene. The substituent that comprises the common root is located at C1.

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10

Name the following benzene compounds.

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More practice…..Page 226 Problem 26

Page 214 Problem 14

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More naming…..

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Interesting Aromatic Compounds

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Reactions of Benzene: Oxidation

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What are the products of oxidation of the following compounds?

Another problem…..Page 213 Problem 12

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Side Chain Bromination

Reaction of an alkylbenzene with N-bromo-succinimide (NBS) and benzoyl peroxide (radical initiator) introduces Br into the side chain.

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Reduction of Aromatic Compounds

Reactions of Benzene: Electrophilic Substitution Vs Electrophilic Addition

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Electrophilic Aromatic Substitution

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Halogenation

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Nitration and Sulfonation

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Friedel-Crafts Alkylation

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Limitations of Friedel Crafts Reactions

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Page 212 Problem 11

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Friedel-Crafts Acylation

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Di- and Polysubstitution

Existing groups on a benzene ring influence further substitution in both orientation and rate

Orientation certain substituents direct new substitution preferentially

toward ortho-para positions, others direct preferentially toward meta positions

Rate certain substituents are activating toward further

substitution, others are deactivating toward further substitution

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-OCH3 is ortho-para directing

Ortho-para Directors

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Meta Directors

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Types of Substituents

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Page 218 Problem 18

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Page 221 Problem 19

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Trisubstituted Benzenes

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Where would the electrophile attack the ring preferentially?

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Predict the major product of each of the following reactions.

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Synthesis of p-Bromobenzoic acid

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The order of steps is important.

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