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

Tautomerization

Organic Chemistry

24. Enolate Chemistry: Reactions at the Alpha-Carbon

Tautomerization

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2:11 minutes

Problem 1c1

Textbook Question

Phenylacetone can form two different enols.
(c) Propose mechanisms for the formation of the first enol in acid.

Verified step by step guidance

Identify the structure of phenylacetone: It consists of a phenyl group (C₆H₅-) attached to a carbonyl group (C=O) via a CH₂ group. The carbonyl group is the reactive site for enol formation.

Understand the concept of enol formation: Enols are formed through keto-enol tautomerism, where a proton is transferred, and a double bond is formed between the alpha-carbon (the carbon adjacent to the carbonyl group) and the carbonyl carbon.

Protonate the carbonyl oxygen: In acidic conditions, the lone pair of electrons on the oxygen atom of the carbonyl group interacts with a proton (H⁺), forming a positively charged oxonium ion (C=O⁺H). This step increases the electrophilicity of the carbonyl carbon.

Deprotonate the alpha-carbon: A base (such as water or another molecule in the acidic medium) abstracts a proton (H⁺) from the alpha-carbon. This generates a carbanion intermediate, which is stabilized by resonance with the positively charged oxonium ion.

Form the enol: The lone pair of electrons on the alpha-carbon forms a double bond with the carbonyl carbon, while the oxonium ion loses a proton to regenerate the neutral hydroxyl group (-OH). This results in the formation of the enol structure, where the alpha-carbon is now part of a C=C double bond, and the oxygen is part of an -OH group.

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Key Concepts

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

Enol Formation

Enols are compounds with a hydroxyl group (-OH) bonded to a carbon atom that is part of a carbon-carbon double bond. The formation of enols typically involves the tautomerization of carbonyl compounds, where the keto form (C=O) converts to the enol form (C=C-OH). Understanding this process is crucial for proposing mechanisms for enol formation, especially in the context of acid-catalyzed reactions.

Acid-Catalyzed Mechanism

In acid-catalyzed reactions, the presence of an acid protonates the carbonyl oxygen, increasing the electrophilicity of the carbonyl carbon. This makes it more susceptible to nucleophilic attack, facilitating the formation of the enol. Recognizing how acids influence the reaction pathway is essential for accurately proposing the mechanism for enol formation from phenylacetone.

Tautomerization

Tautomerization is a chemical reaction that involves the interconversion between two isomers, typically a keto form and an enol form. This process is often facilitated by acid or base catalysis. In the case of phenylacetone, understanding the tautomerization process helps in predicting the stability and formation of the enols, which is key to proposing the correct mechanism.

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Phenylacetone can form two different enols.(c) Propose mechanisms for the formation of the first enol in acid.

Key Concepts

Enol Formation

Acid-Catalyzed Mechanism

Tautomerization

Watch next

Phenylacetone can form two different enols.
(c) Propose mechanisms for the formation of the first enol in acid.