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

Previous problemNext problem

2: minutes

Problem 28b(i)

Textbook Question

b. Explain why the rate of aminolysis of an ester cannot be increased by H⁺.

Verified step by step guidance

Understand the process of aminolysis: Aminolysis is a reaction where an ester reacts with an amine to form an amide and an alcohol. This reaction typically proceeds via a nucleophilic acyl substitution mechanism, where the amine acts as the nucleophile.

Recognize the role of H+ in chemical reactions: Adding H+ (protons) to a reaction mixture typically increases the acidity of the environment. This can protonate certain species, making them more electrophilic or altering their reactivity.

Analyze the effect of H+ on the nucleophile (amine): Amines are basic in nature, and the addition of H+ will protonate the amine, converting it into an ammonium ion (R-NH3+). This protonated form is no longer nucleophilic because it lacks a lone pair of electrons to attack the ester carbonyl carbon.

Examine the effect of H+ on the ester: While H+ can protonate the carbonyl oxygen of the ester, making the carbonyl carbon more electrophilic, this does not compensate for the loss of nucleophilicity of the amine. The reaction rate will not increase because the nucleophile (amine) is no longer effective.

Conclude: The rate of aminolysis of an ester cannot be increased by H+ because the protonation of the amine reduces its nucleophilicity, which is essential for the reaction to proceed. The overall effect of H+ is counterproductive in this context.

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.

Aminolysis

Aminolysis is a nucleophilic substitution reaction where an amine attacks an electrophilic carbon atom in an ester, leading to the formation of an amide and an alcohol. This process involves the nucleophile (amine) replacing the leaving group (alcohol) in the ester. Understanding the mechanism of aminolysis is crucial for analyzing how reaction conditions affect the rate of the reaction.

Role of H+ in Reactions

In organic chemistry, H+ ions can act as catalysts by protonating certain functional groups, making them more electrophilic and thus more reactive. However, in the case of aminolysis of esters, the presence of H+ does not enhance the reaction rate because it can also protonate the amine, reducing its nucleophilicity. This balance is essential to understand why H+ does not facilitate the reaction.

Equilibrium Considerations

The rate of a chemical reaction is often influenced by the position of equilibrium. In the case of aminolysis, if H+ is added, it can shift the equilibrium towards the protonated species, which are less reactive. This shift can hinder the formation of the desired products, illustrating that simply adding acid does not always increase the reaction rate and can sometimes have the opposite effect.

Watch next

Master NAS - The Three Rules with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

Textbook Question

The reaction of a nitrile with an alcohol in the presence of a strong acid forms an N-substituted amide. This reaction, known as the Ritter reaction, does not work with primary alcohols.

b. Why does the Ritter reaction not work with primary alcohols?

Textbook Question

The reaction of a nitrile with an alcohol in the presence of a strong acid forms an N-substituted amide. This reaction, known as the Ritter reaction, does not work with primary alcohols.

c. How does the Ritter reaction differ from the acid-catalyzed hydrolysis of a nitrile to form an amide?

Textbook Question

a. Which of the following reactions does not give the carbonyl product shown?

b. Which of the reactions that do not occur can be made to occur if an acid catalyst is added to the reaction mixture?

Textbook Question

a. Which of the following reactions does not give the carbonyl product shown?

b. Which of the reactions that do not occur can be made to occur if an acid catalyst is added to the reaction mixture?

10.

Textbook Question

b. Explain why the rate of aminolysis of an ester cannot be increased by HO⁻, or RO⁻.

Textbook Question

a. Rank the following esters from most reactive to least reactive in the first slow step of a nucleophilic acyl substitution reaction (formation of the tetrahedral intermediate):

Textbook Question

b. Rank the same esters from most reactive to least reactive in the second slow step of a nucleophilic acyl substitution reaction (collapse of the tetrahedral intermediate).

Textbook Question

In each part, rank the compounds in order of increasing rate of nucleophilic attack at C=O by a strong nucleophile like methoxide.

(a)

Show more practices