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

Nucleophilic Addition

Organic Chemistry

21. Aldehydes and Ketones: Nucleophilic Addition

Nucleophilic Addition

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4:24 minutes

Problem 91

Textbook Question

When a cyclic ketone reacts with diazomethane, the next larger cyclic ketone is formed. This is called a ring-expansion reaction. Draw a mechanism for the following ring-expansion reaction.

Verified step by step guidance

Step 1: Begin by identifying the cyclic ketone and diazomethane as the reactants. Diazomethane (CH₂N₂) is a highly reactive compound that serves as a source of a carbene (a neutral species with a divalent carbon atom). The reaction starts with the nucleophilic attack of the lone pair on the oxygen atom of the ketone on the electrophilic carbon of diazomethane.

Step 2: The nucleophilic attack forms a new bond between the oxygen of the ketone and the carbon of diazomethane. This intermediate is a zwitterion, where the oxygen carries a positive charge and the nitrogen of diazomethane carries a negative charge. This step sets up the system for the next rearrangement.

Step 3: The next step involves the migration of one of the carbon-carbon bonds adjacent to the ketone carbonyl group. This migration is facilitated by the formation of a carbene intermediate. The bond migration expands the ring by one carbon atom, creating a new cyclic structure.

Step 4: The rearrangement results in the formation of a new cyclic ketone with one additional carbon in the ring. The nitrogen from diazomethane is released as molecular nitrogen (N₂), which is a very stable byproduct and drives the reaction forward.

Step 5: Finally, confirm the structure of the product. The new cyclic ketone should have one more carbon in the ring compared to the starting material. Verify that the mechanism is consistent with the principles of organic chemistry, including charge balance and proper electron flow.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Cyclic Ketones

Cyclic ketones are organic compounds that contain a carbonyl group (C=O) within a ring structure. The presence of the carbonyl group influences the reactivity of the molecule, making it susceptible to various reactions, including ring-expansion. Understanding the structure and properties of cyclic ketones is essential for predicting their behavior in chemical reactions.

Ring-Expansion Reaction

A ring-expansion reaction involves the transformation of a smaller cyclic compound into a larger cyclic compound, typically through the addition of new atoms or groups. In the case of cyclic ketones reacting with diazomethane, the reaction leads to the formation of a larger cyclic ketone. This process is significant in organic synthesis as it allows for the construction of more complex molecular architectures.

Mechanism of Reaction

The mechanism of a reaction describes the step-by-step sequence of elementary reactions that occur during the transformation of reactants into products. For the ring-expansion reaction involving cyclic ketones and diazomethane, understanding the mechanism is crucial for illustrating how bonds are broken and formed, and how intermediates are generated. This knowledge helps in predicting the outcome of the reaction and designing synthetic pathways.

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Rank the following compounds from most reactive to least reactive toward nucleophilic addition:

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Rank the following compounds from most reactive to least reactive toward nucleophilic addition:

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Multiple Choice

Which of the following is NOT a reason a ketone is less reactive than an aldehyde?

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When a ketone is dissolved in ¹⁸O-labeled water, the ¹⁸O label is incorporated into the ketone. Suggest a mechanism that explains this observation.

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