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.
(c)
(d)
1298
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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 41
Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 41Chapter 22, Problem 41
Propose a mechanism for the crossed Claisen condensation between ethyl acetate and ethyl benzoate.
Verified step by step guidance1
Step 1: Identify the reactants and the type of reaction. The crossed Claisen condensation involves two esters, ethyl acetate (CH₃COOCH₂CH₃) and ethyl benzoate (C₆H₅COOCH₂CH₃), reacting in the presence of a strong base to form a β-keto ester.
Step 2: Deprotonation of the α-hydrogen. A strong base, such as sodium ethoxide (NaOCH₂CH₃), deprotonates the α-hydrogen of ethyl acetate, forming an enolate ion. The enolate ion is stabilized by resonance, with the negative charge delocalized between the oxygen atom and the α-carbon.
Step 3: Nucleophilic attack of the enolate ion. The enolate ion acts as a nucleophile and attacks the carbonyl carbon of ethyl benzoate. This step forms a tetrahedral intermediate, where the negative charge is temporarily localized on the oxygen atom of the carbonyl group.
Step 4: Collapse of the tetrahedral intermediate. The tetrahedral intermediate collapses, expelling the ethoxide ion (CH₃CH₂O⁻) as a leaving group. This step results in the formation of a β-keto ester, where the two original esters are now connected through a new carbon-carbon bond.
Step 5: Protonation of the product. The β-keto ester formed in the previous step is protonated by the solvent or another proton source, stabilizing the final product. The reaction is complete, yielding the crossed Claisen condensation product.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Claisen Condensation
Claisen condensation is a reaction between two esters or an ester and a carbonyl compound in the presence of a strong base, leading to the formation of a β-keto ester or a β-diketone. This reaction involves the nucleophilic attack of an enolate ion, generated from one of the esters, on the carbonyl carbon of the other ester. Understanding this mechanism is crucial for proposing the crossed Claisen condensation between ethyl acetate and ethyl benzoate.
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Claisen Condensation
Enolate Ion Formation
Enolate ions are formed when a strong base abstracts a proton from the α-carbon of an ester or carbonyl compound, resulting in a resonance-stabilized anion. This enolate ion acts as a nucleophile in the Claisen condensation, attacking the electrophilic carbonyl carbon of another ester. Recognizing how enolate ions are generated and their role in nucleophilic attacks is essential for understanding the mechanism of the crossed Claisen condensation.
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Crossed Claisen Condensation
Crossed Claisen condensation refers to the reaction between two different esters or an ester and a carbonyl compound, which can lead to the formation of a new carbon-carbon bond. This reaction is selective and can yield different products depending on the choice of reactants and the conditions used. Analyzing the specific reactants, such as ethyl acetate and ethyl benzoate, is vital for predicting the outcome and mechanism of the reaction.
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Related Practice
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
views
Textbook Question
Predict the products from crossed Claisen condensation of the following pairs of esters. Indicate which combinations are poor choices for crossed Claisen condensations.
(a)
(b)
883
views
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
views
Textbook Question
Predict the products from crossed Claisen condensation of the following pairs of esters. Indicate which combinations are poor choices for crossed Claisen condensations.
(c)
(d)
709
views
Textbook Question
Show how crossed Claisen condensations could be used to prepare the following esters.
(a)
1001
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