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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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 32e
Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 32eChapter 22, Problem 32e
Show how each compound can be dissected into reagents joined by an aldol condensation, then decide whether the necessary aldol condensation is feasible.
(e) 
Verified step by step guidance1
Step 1: Analyze the given compound structure. The compound contains a ketone functional group (C=O) and an α,β-unsaturated system (double bond adjacent to the carbonyl group). This suggests that the compound could be formed via an aldol condensation reaction.
Step 2: Identify the two fragments that could combine to form the given compound. In an aldol condensation, one fragment acts as the enolate ion (nucleophile) and the other as the electrophile (carbonyl compound). Here, the enolate ion would likely form from the methyl ketone group (CH3CO-) and the electrophile would be cyclohexanone.
Step 3: Write the retrosynthetic disconnection. Break the compound at the α,β-unsaturated bond to identify the two starting materials. The disconnection suggests that the compound can be formed by the reaction of cyclohexanone and acetone (CH3COCH3).
Step 4: Assess the feasibility of the aldol condensation. Cyclohexanone can form an enolate ion under basic conditions, and acetone can act as the electrophile. The reaction is feasible because both components are reactive under typical aldol condensation conditions.
Step 5: Summarize the reaction mechanism. Under basic conditions, cyclohexanone forms an enolate ion, which attacks the carbonyl carbon of acetone. This forms a β-hydroxyketone intermediate, which then undergoes dehydration to yield the α,β-unsaturated ketone product shown in the image.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Aldol Condensation
Aldol condensation is a reaction between aldehydes or ketones that contain alpha-hydrogens, leading to the formation of β-hydroxy aldehydes or ketones. This reaction involves the nucleophilic addition of an enolate ion to a carbonyl compound, followed by dehydration to yield an α,β-unsaturated carbonyl compound. Understanding this process is crucial for dissecting compounds into their respective reagents.
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Crossed Aldol
Enolate Ion Formation
Enolate ions are formed when a base abstracts an alpha-hydrogen from a carbonyl compound, resulting in a resonance-stabilized anion. This ion acts as a nucleophile in aldol reactions, allowing it to attack another carbonyl carbon. Recognizing how enolate ions are generated and their role in aldol condensation is essential for analyzing the feasibility of the reaction.
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Intramolecular Aldol Condensation
Intramolecular aldol condensation occurs when the aldehyde or ketone reacts with itself within the same molecule, forming a cyclic compound. This process is often favored due to the stability of the resulting ring structure. Identifying whether a compound can undergo intramolecular aldol condensation is key to determining the feasibility of the reaction presented in the question.
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03:27Diesters (Dieckmann Condensation)
Related Practice
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
Show how each compound can be dissected into reagents joined by an aldol condensation, then decide whether the necessary aldol condensation is feasible.
(a)
1172
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Textbook Question
The following compound results from base-catalyzed aldol cyclization of a 2-substituted cyclohexanone.
(a) Show the diketone that would cyclize to give this product.
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Textbook Question
Show how each compound can be dissected into reagents joined by an aldol condensation, then decide whether the necessary aldol condensation is feasible.
(b)
746
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Textbook Question
Show how each compound can be dissected into reagents joined by an aldol condensation, then decide whether the necessary aldol condensation is feasible.
(c)
809
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