Textbook Question
Predict the major products of the following reactions:
(d)
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Ch. 18 - Ketones and Aldehydes
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
Chapter 18, Problem 36b
Predict the major products of the following reactions:
(b) 
Verified step by step guidance1
Step 1: Recognize the reaction type. The reagents H₂NNH₂ (hydrazine) and KOH with heat indicate a Wolff-Kishner reduction. This reaction is used to reduce a carbonyl group (C=O) in aldehydes or ketones to a methylene group (-CH₂).
Step 2: Analyze the starting material. The given compound is a ketone with a carbonyl group attached to a secondary carbon. The rest of the molecule consists of alkyl groups branching off the main chain.
Step 3: Understand the mechanism. In the Wolff-Kishner reduction, hydrazine reacts with the carbonyl group to form a hydrazone intermediate. Under basic conditions and heat, the hydrazone undergoes decomposition, resulting in the removal of the oxygen atom and the formation of a methylene group (-CH₂).
Step 4: Predict the product. The carbonyl group in the ketone will be replaced by a methylene group (-CH₂), leaving the rest of the molecule unchanged. The major product will retain the same carbon skeleton as the starting material, but the carbonyl group will be reduced.
Step 5: Verify the structure. Ensure that the major product is consistent with the Wolff-Kishner reduction mechanism and that no other functional groups are affected during the reaction.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Wolff-Kishner Reduction
The Wolff-Kishner reduction is a chemical reaction used to convert carbonyl compounds, such as ketones and aldehydes, into alkanes. This process involves the use of hydrazine (H2NNH2) and a strong base, typically potassium hydroxide (KOH), under heating conditions. The reaction proceeds through the formation of a hydrazone intermediate, which is then deprotonated and subsequently decomposed to yield the corresponding alkane.
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Mechanism
Hydrazine and its Role
Hydrazine (H2NNH2) is a key reagent in the Wolff-Kishner reduction, acting as a nucleophile that reacts with carbonyl compounds to form hydrazones. This intermediate is crucial for the subsequent steps of the reaction, where it undergoes deprotonation and elimination to produce the final alkane product. Understanding the reactivity of hydrazine and its derivatives is essential for predicting the outcomes of reactions involving carbonyl compounds.
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Base-Catalyzed Decomposition
In the Wolff-Kishner reduction, the strong base (KOH) plays a vital role in facilitating the decomposition of the hydrazone intermediate. The base deprotonates the hydrazone, leading to the formation of a carbanion that can eliminate nitrogen gas (N2) and yield the alkane product. This step is critical for the successful conversion of the carbonyl compound to an alkane, highlighting the importance of base strength and reaction conditions in organic synthesis.
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Related Practice
Textbook Question
Propose a mechanism for both parts of the Wolff–Kishner reduction of cyclohexanone: the formation of the hydrazone, and then the base-catalyzed reduction with evolution of nitrogen gas.
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Textbook Question
Draw structures of the following derivatives.
(a) the 2,4-dinitrophenylhydrazone of benzaldehyde
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Textbook Question
Propose a mechanism for both parts of the Wolff–Kishner reduction of cyclohexanone: the formation of the hydrazone, and then the base-catalyzed reduction with evolution of nitrogen gas.
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Textbook Question
Predict the major products of the following reactions:
(c)
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Textbook Question
Predict the major products of the following reactions:
(a)
2
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