Textbook Question
Propose mechanisms for the two Dieckmann condensations just shown.
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Ch. 22 - Condensations and Alpha Substitutions of Carbonyl 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
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Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 39a
Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 39aChapter 22, Problem 39a
Propose mechanisms for the two Dieckmann condensations just shown.
Verified step by step guidance1
Step 1: Identify the starting materials for the Dieckmann condensation. In the first reaction, the starting material is diethyl adipate (a 1,6-diesters), and in the second reaction, the starting material is dimethyl pimelate (a 1,7-diesters). Both are esters with two ester groups separated by a chain of carbons.
Step 2: Recognize the role of the base (−OCH₂CH₃). The base abstracts a proton from the α-carbon (the carbon adjacent to the ester group) to form an enolate ion. This enolate ion is nucleophilic and will attack the carbonyl carbon of the second ester group within the same molecule.
Step 3: Understand the intramolecular nucleophilic attack. The enolate ion formed in Step 2 attacks the carbonyl carbon of the second ester group, leading to the formation of a cyclic intermediate. This step is crucial for the formation of the cyclic β-keto ester product.
Step 4: Analyze the intermediate formed. After the nucleophilic attack, a tetrahedral intermediate is formed. This intermediate undergoes elimination of the ethoxide group (−OCH₂CH₃), resulting in the formation of the cyclic β-keto ester.
Step 5: Confirm the final product. The first reaction yields a five-membered cyclic β-keto ester, while the second reaction yields a six-membered cyclic β-keto ester. These products are stabilized by resonance and are the result of the Dieckmann condensation mechanism.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Dieckmann Condensation
The Dieckmann condensation is a type of intramolecular reaction that involves the formation of a cyclic β-keto ester from a diester in the presence of a strong base. This reaction typically occurs when the base deprotonates one of the ester groups, allowing the resulting enolate to attack the carbonyl carbon of the other ester group, leading to cyclization and subsequent hydrolysis.
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03:27
Diesters (Dieckmann Condensation)
Enolate Formation
Enolate formation is a crucial step in many organic reactions, including the Dieckmann condensation. It involves the deprotonation of a carbonyl compound, resulting in a resonance-stabilized anion known as an enolate. This enolate can act as a nucleophile, attacking electrophilic centers, such as carbonyl carbons, facilitating the formation of new carbon-carbon bonds.
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Mechanistic Pathways
Understanding mechanistic pathways is essential for proposing reaction mechanisms in organic chemistry. A mechanistic pathway outlines the step-by-step sequence of elementary reactions that occur during a chemical transformation. In the context of Dieckmann condensations, it involves identifying the formation of enolates, nucleophilic attacks, and the rearrangement of intermediates to yield the final cyclic product.
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Related Practice
Textbook Question
Show what esters would undergo Claisen condensation to give the following β-keto esters.
(a)
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Textbook Question
Some (but not all) of the following keto esters can be formed by Dieckmann condensations. Determine which ones are possible, and draw the starting diesters.
(a)
(b)
963
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Textbook Question
Show what esters would undergo Claisen condensation to give the following β-keto esters.
(b)
1339
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Textbook Question
Some (but not all) of the following keto esters can be formed by Dieckmann condensations. Determine which ones are possible, and draw the starting diesters.
992
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Textbook Question
Show what esters would undergo Claisen condensation to give the following β-keto esters.
(c)
1023
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