Textbook Question
Propose mechanisms for the Birch reduction of anisole. Show why the observed orientation of reduction is favored in each case.
1527
views
Ch. 17 - Reactions of Aromatic Compounds
Wade9th EditionOrganic ChemistryISBN: 9780135213728
Not the one you use?Change textbookSelect a different textbook
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 31a
Propose mechanisms for the Birch reduction of benzoic acid. Show why the observed orientation of reduction is favored in each case.
Verified step by step guidance1
Step 1: Understand the Birch reduction mechanism. The Birch reduction involves the reduction of aromatic compounds using alkali metals (e.g., sodium or lithium) in liquid ammonia, typically in the presence of an alcohol as a proton source. This reaction leads to the formation of 1,4-cyclohexadienes.
Step 2: Analyze the structure of benzoic acid. Benzoic acid contains a benzene ring with a carboxylic acid (-COOH) group attached. The electron-withdrawing nature of the carboxylic acid group influences the orientation of the reduction.
Step 3: Explain the regioselectivity of the Birch reduction. In the Birch reduction, electron-withdrawing groups like -COOH stabilize the negative charge formed during the reaction. This stabilization occurs at positions ortho and para to the electron-withdrawing group, leading to selective reduction of the benzene ring at the meta positions relative to the -COOH group.
Step 4: Propose the mechanism. The mechanism begins with the transfer of an electron from the alkali metal to the benzene ring, forming a radical anion. The radical anion is stabilized by the electron-withdrawing -COOH group. Protonation from the alcohol follows, and subsequent electron transfers and protonations lead to the formation of the 1,4-cyclohexadiene product.
Step 5: Summarize why the observed orientation is favored. The electron-withdrawing -COOH group directs the reduction to occur at the meta positions due to stabilization of the intermediate radical anion. This regioselectivity ensures the formation of the most stable product during the Birch reduction of benzoic acid.
Verified video answer for a similar problem:
This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
5mWas this helpful?
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 from aromatic rings. Understanding the mechanism of this reduction is crucial, as it helps predict the orientation and products formed during the reaction.
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 either activate or deactivate the ring towards further substitution. In the context of Birch reductions, recognizing how substituents affect the reactivity and orientation of the aromatic compound is essential.
Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple possibilities exist. In Birch reductions, the regioselectivity is determined by the stability of the intermediates formed during the reaction. Analyzing the factors that influence regioselectivity, such as sterics and electronics, is key to understanding why certain products are favored in the reduction of benzoic acid.
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.
(b)
624
views
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
views
Textbook Question
What products would you expect from the following Suzuki coupling reactions?
(b)
1585
views
Textbook Question
Predict the major products of the following reactions.
(b) benzamide (PhCONH2) + Na (liquid NH3, CH3CH2OH)
2065
views
Textbook Question
Predict the major products of the following reactions.
(a) toluene + excess Cl2 (heat, pressure)
1494
views