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

Previous problemNext problem

1:44 minutes

Problem 1c4

Textbook Question

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

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 molecule is CH₃-CO-CH₂-C₆H₅.

Understand enol formation: Enols are formed by the tautomerization of ketones or aldehydes. In the presence of a base, the alpha-hydrogen (hydrogen on the carbon adjacent to the carbonyl group) is abstracted, leading to the formation of an enolate ion, which can then tautomerize to form the enol.

Propose the mechanism for the second enol formation: (1) A base (e.g., OH⁻) abstracts the alpha-hydrogen from the CH₃ group adjacent to the carbonyl group, forming an enolate ion. (2) The negative charge on the enolate ion delocalizes between the alpha-carbon and the oxygen atom of the carbonyl group, creating resonance structures.

Explain the tautomerization step: The enolate ion undergoes protonation at the oxygen atom, leading to the formation of the enol. The second enol is formed when the double bond is between the alpha-carbon and the carbonyl carbon, and the hydroxyl group (-OH) is attached to the carbonyl carbon.

Summarize the key points: The second enol is formed through base-catalyzed deprotonation of the alpha-hydrogen, resonance stabilization of the enolate ion, and subsequent protonation to yield the enol with a different double bond and hydroxyl group arrangement compared to the first enol.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

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

Enol Formation

Enol formation involves the conversion of a carbonyl compound, such as a ketone or aldehyde, into its corresponding enol form, which features a double bond between a carbon and an adjacent carbon with a hydroxyl group. This process is often facilitated by acid or base catalysis, where the base abstracts a proton from the alpha carbon, leading to the formation of a resonance-stabilized enolate ion that can then re-protonate to form the enol.

Base Catalysis

Base catalysis refers to the use of a base to facilitate a chemical reaction. In the context of enol formation, a base can deprotonate the alpha carbon of a carbonyl compound, generating an enolate ion. This ion is more nucleophilic and can participate in further reactions, such as nucleophilic addition or rearrangement, ultimately leading to the formation of different enol isomers.

Tautomerization

Tautomerization is a chemical equilibrium between two isomers, typically involving the migration of a hydrogen atom and a switch of a double bond. In the case of phenylacetone, the keto form can tautomerize to the enol form, and this process can yield different enol structures depending on the reaction conditions. Understanding tautomerization is crucial for predicting the products of reactions involving carbonyl compounds.

Watch next

Master Unusual Acidity of the Alpha Carbon with a bite sized video explanation from Johnny

Start learning

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

Key Concepts

Enol Formation

Base Catalysis

Tautomerization

Watch next

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