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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2:15 minutes

Problem 64b

Textbook Question

A β-ɣ-unsaturated carbonyl compound rearranges to a more stable conjugated ⍺,β-unsaturated compound in the presence of either acid or base. b. Propose a mechanism for the acid-catalyzed rearrangement.

Verified step by step guidance

Step 1: Protonation of the carbonyl oxygen occurs in the presence of the acid (H₃O⁺), making the carbonyl group more electrophilic. This step increases the reactivity of the molecule and prepares it for rearrangement.

Step 2: A resonance-stabilized carbocation is formed by shifting the π-electrons of the double bond towards the positively charged carbonyl carbon. This creates a new intermediate with a positive charge on the β-carbon.

Step 3: A hydride shift or proton transfer occurs from the β-carbon to the α-carbon, stabilizing the carbocation and forming a new double bond between the α- and β-carbons. This step is crucial for the rearrangement to the conjugated structure.

Step 4: Deprotonation of the hydroxyl group (formed during protonation) occurs, regenerating the acid catalyst and completing the rearrangement. The molecule now exists as a conjugated α,β-unsaturated carbonyl compound.

Step 5: The final product is stabilized due to conjugation between the carbonyl group and the double bond, which lowers the overall energy of the molecule and makes it more thermodynamically favorable.

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Key Concepts

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

b,g-Unsaturated Carbonyl Compounds

b,g-Unsaturated carbonyl compounds contain a carbonyl group (C=O) adjacent to a double bond (C=C). This structure allows for unique reactivity, particularly in rearrangements and tautomerizations, where the stability of the conjugated system can drive the reaction. Understanding the electronic and steric factors influencing these compounds is crucial for predicting their behavior in acid or base-catalyzed reactions.

Acid-Catalyzed Mechanism

In acid-catalyzed reactions, protons (H+) from the acid facilitate the rearrangement of the substrate. The mechanism typically involves protonation of the carbonyl oxygen, increasing its electrophilicity, followed by nucleophilic attack by the double bond. This process can lead to the formation of more stable conjugated systems, as seen in the rearrangement of b,g-unsaturated carbonyl compounds.

Tautomerization

Tautomerization is a chemical reaction that involves the transfer of a proton and the rearrangement of bonds, resulting in the interconversion of structural isomers. In the context of b,g-unsaturated carbonyl compounds, tautomerization can lead to the formation of more stable isomers, such as a,b-unsaturated carbonyl compounds. This process is often facilitated by acid or base, highlighting the importance of proton transfer in organic reactions.

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