Textbook Question
Predict the major products of the following base-catalyzed aldol condensations with dehydration.
(a) benzophenone (PhCOPh) + propionaldehyde
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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 31
Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 31Chapter 22, Problem 31
When cyclodecane-1,6-dione is treated with sodium carbonate, the product gives a UV spectrum similar to that of 1-acetyl-2-methylcyclopentene. Propose a structure for the product, and give a mechanism for its formation.
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Identify the starting material, cyclodecane-1,6-dione, which is a cyclic diketone with ketone groups at positions 1 and 6. Recognize that the reaction involves sodium carbonate, a weak base, which can facilitate enolate formation and intramolecular reactions.
Consider the possibility of an intramolecular aldol condensation. Sodium carbonate can deprotonate one of the alpha-hydrogens adjacent to a ketone group, forming an enolate ion. This enolate can act as a nucleophile and attack the carbonyl carbon of the other ketone group within the same molecule.
Propose the formation of a new carbon-carbon bond between the enolate and the carbonyl carbon, resulting in a beta-hydroxyketone intermediate. This intermediate is unstable under the reaction conditions and will undergo dehydration (loss of water) to form an alpha, beta-unsaturated ketone.
Analyze the UV spectrum similarity to 1-acetyl-2-methylcyclopentene. This suggests the product contains a conjugated system, likely a cyclopentene ring with an alpha, beta-unsaturated ketone functional group. The reaction likely involves ring contraction from the 10-membered ring to a 5-membered ring during the aldol condensation.
Propose the final product structure as 2-methyl-5-cyclopentenone, which is consistent with the UV spectrum data and the mechanism of intramolecular aldol condensation followed by dehydration.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Cyclodecane-1,6-dione Structure
Cyclodecane-1,6-dione is a cyclic diketone with two carbonyl groups located at the 1 and 6 positions of a ten-membered carbon ring. Understanding its structure is crucial for predicting how it will react with sodium carbonate, as the presence of carbonyl groups can influence reactivity and the formation of new bonds during the reaction.
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Mechanism of Nucleophilic Attack
The reaction of cyclodecane-1,6-dione with sodium carbonate likely involves a nucleophilic attack on the carbonyl carbon by a carbonate ion. This mechanism is essential for understanding how the product is formed, as it illustrates the steps involved in the conversion of the diketone to the final product, including any intermediate species that may arise during the reaction.
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UV Spectroscopy in Organic Chemistry
UV spectroscopy is a technique used to analyze the electronic transitions in molecules, particularly those with conjugated systems. The similarity in UV spectra between the product and 1-acetyl-2-methylcyclopentene suggests that the product likely contains a similar conjugated system, which is important for deducing the structure of the product and understanding its stability and reactivity.
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Related Practice
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)
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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)
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Textbook Question
Predict the major products of the following base-catalyzed aldol condensations with dehydration.
(b) 2,2-dimethylpropanal + acetophenone
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Textbook Question
Show how octane-2,7-dione might cyclize to a cycloheptenone. Explain why ring closure to the cycloheptenone is not favored.
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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)
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