Textbook Question
For each molecule shown below,
1. indicate the most acidic hydrogens.
2. draw the important resonance contributors of the anion that results from removal of the most acidic hydrogen.
(h)
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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 62a
Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblem 62aChapter 22, Problem 62a
Predict the products of the following aldol condensations. Show the products both before and after dehydration.
(a) 
Verified step by step guidance1
Step 1: Identify the reactants and the type of reaction. The given reaction involves an aldol condensation, which typically occurs between an aldehyde or ketone with an α-hydrogen in the presence of a base (here, -OH). The reactant is isobutyraldehyde (CH3)2CHCH2CHO.
Step 2: Determine the enolate formation. In the presence of a base, the α-hydrogen (hydrogen attached to the carbon adjacent to the carbonyl group) is abstracted, forming an enolate ion. The enolate ion is resonance-stabilized, with the negative charge delocalized between the α-carbon and the oxygen of the carbonyl group.
Step 3: Perform the nucleophilic attack. The enolate ion acts as a nucleophile and attacks the carbonyl carbon of another molecule of isobutyraldehyde. This forms a β-hydroxyaldehyde intermediate, which is the product before dehydration.
Step 4: Dehydration step. Under the reaction conditions, the β-hydroxyaldehyde undergoes dehydration (loss of water) to form an α,β-unsaturated aldehyde. This step involves the elimination of a hydroxyl group (-OH) and a hydrogen atom from the β-carbon and α-carbon, respectively, resulting in the formation of a double bond between the α- and β-carbons.
Step 5: Write the final products. The product before dehydration is the β-hydroxyaldehyde, and the product after dehydration is the α,β-unsaturated aldehyde. Ensure the chemical structures are drawn correctly to reflect these transformations.
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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 predicting the products of the reaction.
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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, attacking the carbonyl carbon of another molecule. Recognizing how enolate ions are generated and their role in the reaction mechanism is essential for predicting the products of aldol condensations.
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Dehydration Step
The dehydration step in aldol condensation involves the elimination of a water molecule from the β-hydroxy carbonyl compound, resulting in the formation of an α,β-unsaturated carbonyl compound. This step is driven by the stability of the resulting double bond and is crucial for completing the reaction. Understanding this step helps in identifying the final products of the aldol condensation process.
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Related Practice
Textbook Question
Predict the products of the following aldol condensations. Show the products both before and after dehydration.
(d)
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Textbook Question
2. Indicate which compounds would be more than 99% deprotonated by a solution of sodium ethoxide in ethanol.
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1
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Textbook Question
Predict the products of the following aldol condensations. Show the products both before and after dehydration.
(b)
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Textbook Question
Predict the products of the following aldol condensations. Show the products both before and after dehydration.
(c)
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Textbook Question
1. Rank the following compounds in order of increasing acidity.
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