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

24. Enolate Chemistry: Reactions at the Alpha-Carbon

Acid-Catalyzed Alpha-Halogentation

Organic Chemistry

24. Enolate Chemistry: Reactions at the Alpha-Carbon

Acid-Catalyzed Alpha-Halogentation

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6:30 minutes

Problem 69a

Textbook Question

Predict the products of the following reactions.
(a) cyclopentanone + Br₂ in acetic acid

Verified step by step guidance

Identify the type of reaction: The reaction involves cyclopentanone and bromine (Br₂) in acetic acid. This is a halogenation reaction under acidic conditions, specifically an alpha-halogenation of a ketone.

Determine the reactive site: In acidic conditions, the alpha-hydrogens (hydrogens attached to the carbon adjacent to the carbonyl group) of cyclopentanone are acidic and can be removed to form an enol intermediate.

Form the enol intermediate: The carbonyl oxygen of cyclopentanone is protonated by the acidic medium, increasing the electrophilicity of the carbonyl carbon. This facilitates the formation of the enol tautomer by deprotonation of an alpha-hydrogen.

React the enol with bromine: The enol intermediate reacts with Br₂, where the double bond of the enol attacks the bromine molecule. This results in the substitution of one alpha-hydrogen with a bromine atom, forming an alpha-bromoketone.

Conclude the product: The final product is an alpha-brominated cyclopentanone, where one of the alpha-hydrogens has been replaced by a bromine atom. Ensure to consider regioselectivity if there are multiple alpha-hydrogens.

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Key Concepts

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

Electrophilic Aromatic Substitution

Electrophilic aromatic substitution is a fundamental reaction mechanism in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. In the case of cyclopentanone, while it is not an aromatic compound, understanding this mechanism is crucial for predicting how electrophiles like Br2 interact with carbonyl compounds. The presence of acetic acid as a solvent can also influence the reaction pathway and product formation.

Halogenation of Ketones

Halogenation of ketones involves the substitution of a hydrogen atom in the ketone structure with a halogen atom, such as bromine. This reaction typically occurs at the alpha position relative to the carbonyl group, leading to the formation of alpha-halo ketones. The reaction conditions, including the solvent and temperature, can significantly affect the regioselectivity and yield of the halogenated product.

Reactivity of Carbonyl Compounds

Carbonyl compounds, such as ketones and aldehydes, exhibit unique reactivity due to the polarized carbon-oxygen double bond. This polarization makes the carbon atom electrophilic, allowing it to react with nucleophiles and electrophiles. Understanding the reactivity of carbonyl compounds is essential for predicting the outcomes of reactions involving cyclopentanone and Br2, as it determines how the carbonyl will interact with the halogen.

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