Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

21. Aldehydes and Ketones: Nucleophilic Addition

Wolff Kishner Reduction

Organic Chemistry

21. Aldehydes and Ketones: Nucleophilic Addition

Wolff Kishner Reduction

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6:48 minutes

Problem 35a

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.

Verified step by step guidance

Step 1: Formation of the hydrazone - Start with cyclohexanone (a ketone) and hydrazine (NH₂NH₂). The carbonyl group (C=O) of cyclohexanone reacts with hydrazine in the presence of an acid catalyst. This involves nucleophilic attack by the lone pair on the nitrogen of hydrazine on the electrophilic carbon of the carbonyl group, forming a tetrahedral intermediate.

Step 2: Proton transfer - In the tetrahedral intermediate, a proton transfer occurs, leading to the elimination of water (H₂O) and the formation of a double bond between the carbon and nitrogen. This results in the formation of the hydrazone (C=N-NH₂).

Step 3: Base-catalyzed reduction - In the second part of the mechanism, the hydrazone is treated with a strong base, such as KOH, and heat. The base deprotonates the terminal nitrogen (NH₂ group), forming a resonance-stabilized anion.

Step 4: Nitrogen gas evolution - The resonance-stabilized anion undergoes further deprotonation and rearrangement, leading to the cleavage of the N-N bond and the release of nitrogen gas (N₂). This step is driven by the stability of nitrogen gas as a product.

Step 5: Formation of the alkane - The remaining carbon fragment is protonated by water or another proton source, resulting in the formation of cyclohexane, the fully reduced product.

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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 formation of a hydrazone intermediate, which is then treated with a strong base, typically hydrazine and potassium hydroxide, to facilitate the removal of nitrogen gas and reduce the carbonyl compound.

Formation of Hydrazone

The formation of a hydrazone occurs when a carbonyl compound reacts with hydrazine. This reaction involves the nucleophilic attack of the hydrazine on the carbonyl carbon, leading to the formation of a C=N bond. The resulting hydrazone is a key intermediate in the Wolff–Kishner reduction, which stabilizes the carbonyl compound for subsequent reduction.

Base-Catalyzed Reduction

In the base-catalyzed reduction step of the Wolff–Kishner reaction, the hydrazone undergoes deprotonation by a strong base, generating a reactive intermediate. This intermediate then eliminates nitrogen gas, resulting in the formation of an alkane. The evolution of nitrogen gas is a driving force for the reaction, facilitating the conversion of the hydrazone to the final hydrocarbon product.

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