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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8:05 minutes

Problem 45

Textbook Question

We saw that acid anhydrides react with alcohols, water, and amines. In which of these reactions can the tetrahedral intermediate eliminate the carboxylate ion even if it does not lose a proton before the elimination step? Explain.

Verified step by step guidance

Step 1: Understand the reaction mechanism of acid anhydrides with alcohols, water, and amines. Acid anhydrides are reactive compounds that undergo nucleophilic acyl substitution reactions. The key intermediate in these reactions is a tetrahedral intermediate formed when the nucleophile attacks the carbonyl carbon.

Step 2: Analyze the elimination step in the reaction mechanism. The tetrahedral intermediate can eliminate a leaving group, such as a carboxylate ion, without losing a proton if the leaving group is already negatively charged. This is because the carboxylate ion is a stable leaving group due to resonance stabilization.

Step 3: Examine the nucleophiles provided in the image: ethanol (CH₃CH₂OH), ethylamine (CH₃CH₂NH₂), and water (H₂O). Ethanol and water are neutral nucleophiles, meaning they will likely lose a proton before elimination occurs. Ethylamine, however, is a basic nucleophile and can form a tetrahedral intermediate where the carboxylate ion is eliminated directly without proton loss.

Step 4: Consider the role of the nucleophile's basicity and the stability of the leaving group. Amines, such as ethylamine, are stronger nucleophiles and can facilitate direct elimination of the carboxylate ion due to their ability to stabilize the intermediate without requiring proton transfer.

Step 5: Conclude that the reaction of acid anhydrides with amines (e.g., CH₃CH₂NH₂) allows the tetrahedral intermediate to eliminate the carboxylate ion directly, even without losing a proton before the elimination step. This is due to the inherent properties of the amine nucleophile and the stability of the carboxylate ion.

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Key Concepts

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

Tetrahedral Intermediate

A tetrahedral intermediate is a transient species formed during nucleophilic acyl substitution reactions, where a nucleophile attacks the carbonyl carbon of a carboxylic acid derivative. This intermediate has a tetrahedral geometry due to the addition of the nucleophile, which temporarily disrupts the carbonyl's planar structure. Understanding this concept is crucial for analyzing how the intermediate can lead to the elimination of leaving groups, such as carboxylate ions.

Carboxylate Ion

A carboxylate ion is the conjugate base of a carboxylic acid, formed when the acid loses a proton from its carboxyl group. In the context of acid anhydrides, the carboxylate ion can act as a leaving group during nucleophilic substitution reactions. Recognizing the role of the carboxylate ion is essential for understanding the conditions under which it can be eliminated from the tetrahedral intermediate without prior proton loss.

Nucleophilic Acyl Substitution

Nucleophilic acyl substitution is a fundamental reaction in organic chemistry where a nucleophile attacks the electrophilic carbon of a carbonyl compound, leading to the substitution of a leaving group. This reaction is characteristic of carboxylic acid derivatives, including acid anhydrides, esters, and amides. Grasping this concept helps in predicting the outcomes of reactions involving acid anhydrides with alcohols, amines, and water, particularly in the context of tetrahedral intermediates.

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