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

22. Carboxylic Acid Derivatives: NAS

Nucleophilic Acyl Substitution

Organic Chemistry

22. Carboxylic Acid Derivatives: NAS

Nucleophilic Acyl Substitution

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3:55 minutes

Problem 84b

Textbook Question

Propose a mechanism for each of the following reactions:
b.

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Step 1: Analyze the starting material and the product. The starting material is a cyclic diketone, and the product is a phenol with a carboxylic acid side chain. This suggests a ring-opening reaction followed by rearrangement under acidic conditions.

Step 2: Protonation of one of the carbonyl groups occurs first under acidic conditions (H3O+), making the carbonyl carbon more electrophilic and susceptible to nucleophilic attack.

Step 3: Water acts as a nucleophile and attacks the protonated carbonyl group, leading to the formation of a tetrahedral intermediate. This intermediate undergoes rearrangement to open the ring structure.

Step 4: The ring-opening leads to the formation of a linear intermediate. Subsequent proton transfers and tautomerization occur, converting one of the ketone groups into a hydroxyl group (phenol formation).

Step 5: The other carbonyl group undergoes hydrolysis to form a carboxylic acid. The final product is stabilized by resonance in the aromatic ring and the carboxylic acid group.

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Key Concepts

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

Nucleophilic Acyl Substitution

Nucleophilic acyl substitution is a fundamental reaction in organic chemistry where a nucleophile attacks an acyl compound, leading to the replacement of a leaving group. In this mechanism, the nucleophile, often a water molecule in the presence of acid, attacks the carbonyl carbon, forming a tetrahedral intermediate. This intermediate then collapses, expelling the leaving group and forming a new carbonyl compound.

Role of H3O+ in Acid-Catalyzed Reactions

H3O+ (hydronium ion) acts as a catalyst in acid-catalyzed reactions, enhancing the electrophilicity of carbonyl compounds. In the context of nucleophilic acyl substitution, H3O+ protonates the carbonyl oxygen, increasing the positive charge on the carbonyl carbon and making it more susceptible to nucleophilic attack. This step is crucial for facilitating the reaction and ensuring a higher reaction rate.

Tetrahedral Intermediate

The tetrahedral intermediate is a key species formed during nucleophilic acyl substitution. When the nucleophile attacks the carbonyl carbon, the sp2 hybridization of the carbon changes to sp3, resulting in a tetrahedral geometry. This intermediate is unstable and typically collapses to reform the carbonyl group, leading to the release of the leaving group and the formation of the final product.

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Propose a mechanism for each of the following reactions:b.

Key Concepts

Nucleophilic Acyl Substitution

Role of H3O+ in Acid-Catalyzed Reactions

Tetrahedral Intermediate

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Propose a mechanism for each of the following reactions:
b.