Textbook Question
Starting from toluene, propose a synthesis of this trisubstituted benzene.
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Ch. 17 - Reactions of Aromatic Compounds
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 17, Problem 50a,b
Predict the major products formed when benzene reacts (just once) with the following reagents.
a. tert-butyl bromide, AlCl3
b. 1-chlorobutane, AlCl3
Verified step by step guidance1
Step 1: Recognize that the reaction involves benzene and an alkyl halide in the presence of AlCl₃, which is a Friedel-Crafts alkylation reaction. This reaction introduces an alkyl group onto the benzene ring.
Step 2: For part (a), tert-butyl bromide (C(CH₃)₃Br) reacts with AlCl₃ to form a tert-butyl carbocation (C(CH₃)₃⁺) as the electrophile. This occurs because AlCl₃ acts as a Lewis acid, abstracting the bromide ion (Br⁻) from tert-butyl bromide.
Step 3: The tert-butyl carbocation then reacts with the benzene ring via electrophilic aromatic substitution. The π-electrons of the benzene ring attack the carbocation, forming a sigma complex (arenium ion). This intermediate is stabilized by resonance.
Step 4: The sigma complex loses a proton (H⁺) to restore aromaticity, resulting in the formation of tert-butylbenzene as the major product.
Step 5: For part (b), 1-chlorobutane (CH₃CH₂CH₂CH₂Cl) reacts with AlCl₃ to form a primary butyl carbocation (CH₃CH₂CH₂CH₂⁺). However, primary carbocations are unstable and undergo hydride shifts to form a more stable secondary carbocation (CH₃CH₂CH⁺CH₃). This secondary carbocation then reacts with benzene in the same manner as described in steps 3 and 4, leading to the formation of sec-butylbenzene as the major product.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Aromatic Substitution
Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. This process is crucial for understanding how benzene and its derivatives react with various reagents, as it preserves the aromaticity of the ring while introducing new substituents.
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EAS Review
Friedel-Crafts Alkylation
Friedel-Crafts alkylation is a specific type of electrophilic aromatic substitution that involves the introduction of an alkyl group onto an aromatic ring using an alkyl halide and a Lewis acid catalyst, such as AlCl3. This reaction can lead to the formation of branched or linear alkyl groups, depending on the structure of the alkyl halide used.
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Rearrangement of Carbocations
The stability and rearrangement of carbocations play a critical role in reactions involving alkyl halides. When an alkyl halide reacts in a Friedel-Crafts alkylation, the formation of a carbocation intermediate can lead to rearrangements, resulting in more stable carbocations, which can affect the final product distribution.
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Related Practice
Textbook Question
Predict the major products formed when benzene reacts (just once) with the following reagents.
e. isobutylene + HF
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Textbook Question
Propose a synthetic sequence of this trisubstituted benzene starting from toluene.
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Textbook Question
Predict the major products formed when benzene reacts (just once) with the following reagents.
c. isobutyl alcohol + BF3
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Textbook Question
To synthesize m-ethylbenzenesulfonic acid, a student attempted the Friedel–Crafts alkylation of benzenesulfonic acid with bromoethane. Do you predict that this reaction was successful? If not, propose an alternative synthesis.
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Textbook Question
Predict the major products formed when benzene reacts (just once) with the following reagents.
d. bromine + a nail
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