Textbook Question
Show how you would use Suzuki reactions to synthesize these products from the indicated starting materials. You may use any additional reagents you need.
(b)
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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 31b
Propose mechanisms for the Birch reduction of anisole. Show why the observed orientation of reduction is favored in each case.
Verified step by step guidance1
Understand the Birch reduction: The Birch reduction is a reaction where aromatic rings are partially reduced to form 1,4-cyclohexadienes using a combination of sodium (or lithium), liquid ammonia, and an alcohol. The reaction involves electron transfer and protonation steps.
Analyze the substrate: Anisole (methoxybenzene) has a methoxy (-OCH₃) group, which is an electron-donating group (EDG) through resonance and inductive effects. This group influences the regioselectivity of the reduction by stabilizing certain intermediates.
Propose the mechanism: (1) The sodium metal donates an electron to the aromatic ring, forming a radical anion. (2) The radical anion is stabilized by resonance, with the negative charge delocalized onto the ortho and para positions relative to the methoxy group. (3) Protonation occurs at the position where the negative charge is most stabilized, typically at the meta position relative to the methoxy group. (4) A second electron is added, forming a dianion, which is again stabilized by resonance. (5) A second protonation step completes the reduction, yielding a 1,4-cyclohexadiene product.
Explain the observed orientation: The methoxy group stabilizes the negative charge at the ortho and para positions through resonance. However, steric hindrance makes the ortho position less favorable for protonation. As a result, the para position is more likely to be reduced, leading to the observed regioselectivity.
Summarize the favored product: The Birch reduction of anisole typically results in a 1,4-cyclohexadiene where the double bonds are positioned such that the methoxy group remains conjugated with one of the double bonds, maximizing stability. This regioselectivity is driven by electronic and steric factors.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Birch Reduction
The Birch reduction is a chemical reaction that involves the reduction of aromatic compounds using alkali metals in liquid ammonia, often in the presence of an alcohol. This reaction typically leads to the formation of 1,4-cyclohexadienes. Understanding the Birch reduction mechanism is crucial for predicting the products and the orientation of the reduction, as it involves the formation of radical anions and their subsequent protonation.
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. The orientation of substitution is influenced by the substituents already present on the ring, which can be activating or deactivating. In the case of anisole, the methoxy group is an electron-donating group that directs electrophilic attack to the ortho and para positions, affecting the outcome of the Birch reduction.
Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple possibilities exist. In the context of Birch reduction of anisole, the regioselectivity is influenced by the stability of the intermediates formed during the reaction. The orientation of reduction is favored at the positions that lead to more stable radical anions, which is essential for predicting the major products of the reaction.
Related Practice
Textbook Question
Show how you would use Suzuki reactions to synthesize these products from the indicated starting materials. You may use any additional reagents you need.
(a)
1002
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Textbook Question
Predict the major products of the following reactions.
(b) benzamide (PhCONH2) + Na (liquid NH3, CH3CH2OH)
2065
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Textbook Question
Predict the major products of the following reactions.
(c) o-xylene + H2 (1000 psi, 100 °C, Rh catalyst)
1346
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Textbook Question
Propose mechanisms for the Birch reduction of benzoic acid. Show why the observed orientation of reduction is favored in each case.
777
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Textbook Question
Predict the major products of the following reactions.
(a) toluene + excess Cl2 (heat, pressure)
1494
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