Textbook Question
Predict the products of self-condensation of the following esters.
(d)
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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 36a,b
Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 36a,bChapter 22, Problem 36a,b
Predict the products of self-condensation of the following esters.
(a) methyl propanoate + NaOCH3
(b) ethyl phenylacetate + NaOCH2CH3
Verified step by step guidance1
Step 1: Recognize that the reaction involves the Claisen condensation, a reaction where esters undergo self-condensation in the presence of a strong base to form β-keto esters. The base used must match the alkoxide group of the ester to avoid transesterification.
Step 2: For part (a), methyl propanoate reacts with sodium methoxide (NaOCH3). Deprotonation of the α-hydrogen (hydrogen on the carbon adjacent to the carbonyl group) by the base generates an enolate ion. Write the enolate ion structure for methyl propanoate.
Step 3: The enolate ion then acts as a nucleophile and attacks the carbonyl carbon of another molecule of methyl propanoate. This forms a tetrahedral intermediate. Write the structure of the tetrahedral intermediate.
Step 4: The tetrahedral intermediate collapses, expelling a methoxide ion (CH3O⁻) as the leaving group. This results in the formation of a β-keto ester. Write the structure of the β-keto ester product for part (a).
Step 5: For part (b), ethyl phenylacetate reacts with sodium ethoxide (NaOCH2CH3). Follow the same steps as in part (a): deprotonation of the α-hydrogen to form the enolate ion, nucleophilic attack on another molecule of ethyl phenylacetate, formation of the tetrahedral intermediate, and expulsion of the ethoxide ion to yield the β-keto ester product. Write the structure of the β-keto ester product for part (b).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Self-Condensation of Esters
Self-condensation of esters involves the reaction of an ester with itself in the presence of a strong base, leading to the formation of β-keto esters or other products. This reaction typically occurs through a nucleophilic acyl substitution mechanism, where the base deprotonates the ester, allowing it to act as a nucleophile and attack another ester molecule.
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Condensation Reactions
Role of Strong Bases
Strong bases, such as sodium methoxide (NaOCH3) or sodium ethoxide (NaOCH2CH3), are crucial in ester self-condensation as they facilitate the deprotonation of the ester. This creates a reactive alkoxide ion that can initiate nucleophilic attack on another ester molecule, promoting the formation of new carbon-carbon bonds and leading to the desired condensation products.
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Formation of β-Keto Esters
The self-condensation of esters often results in the formation of β-keto esters, which are characterized by a carbonyl group adjacent to an ester group. This structure is significant in organic synthesis as it can undergo further reactions, such as decarboxylation or hydrolysis, leading to a variety of useful compounds in organic chemistry.
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Related Practice
Textbook Question
Esters with only one α hydrogen generally give poor yields in the Claisen condensation. Propose a mechanism for the Claisen condensation of ethyl isobutyrate, and explain why a poor yield is obtained.
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Textbook Question
The following compound results from base-catalyzed aldol cyclization of a 2-substituted cyclohexanone.
(b) Propose a mechanism for the cyclization.
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Textbook Question
Propose a mechanism for the self-condensation of methyl 3-phenylpropionate promoted by sodium methoxide.
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Textbook Question
Ethoxide is used as the base in the condensation of ethyl acetate to avoid some unwanted side reactions. Show what side reactions would occur if the following bases were used.
(a) sodium methoxide
(b) sodium hydroxide
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Textbook Question
Predict the products of self-condensation of the following esters.
(c)
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