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

Fischer Esterification

Organic Chemistry

22. Carboxylic Acid Derivatives: NAS

Fischer Esterification

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2:30 minutes

Problem 78

Textbook Question

a. A student did not obtain any ester when he added 2,4,6-trimethylbenzoic acid to an acidic solution of ethanol. Why? (HINT: Build models.)
b. Would he have encountered the same problem if he had tried to synthesize the methyl ester of 4-methylbenzoic acid in the same way?

Verified step by step guidance

Step 1: Understand the reaction mechanism for esterification. Esterification is typically carried out by reacting a carboxylic acid with an alcohol in the presence of an acid catalyst. The reaction proceeds via a nucleophilic attack of the alcohol on the carbonyl carbon of the carboxylic acid, followed by the elimination of water.

Step 2: Analyze the structure of 2,4,6-trimethylbenzoic acid. This compound has three bulky methyl groups attached to the benzene ring at positions 2, 4, and 6. These groups create significant steric hindrance around the carboxylic acid group, making it difficult for the ethanol molecule to approach and react with the carbonyl carbon.

Step 3: Consider the role of steric hindrance in the reaction. The steric hindrance caused by the bulky methyl groups prevents the nucleophilic ethanol from effectively attacking the carbonyl carbon of the carboxylic acid. As a result, the esterification reaction does not proceed, and no ester is formed.

Step 4: Compare this to 4-methylbenzoic acid. In this compound, there is only one methyl group at the 4-position of the benzene ring. This single methyl group does not create significant steric hindrance around the carboxylic acid group, allowing the ethanol to approach and react with the carbonyl carbon more easily.

Step 5: Conclude that the student would not encounter the same problem with 4-methylbenzoic acid. The reduced steric hindrance in this case would allow the esterification reaction to proceed, resulting in the formation of the methyl ester.

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Key Concepts

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

Esterification Reaction

Esterification is a chemical reaction between an alcohol and a carboxylic acid, resulting in the formation of an ester and water. This process typically requires an acid catalyst to proceed efficiently. In the case of 2,4,6-trimethylbenzoic acid and ethanol, steric hindrance from the bulky methyl groups can impede the reaction, preventing ester formation.

Steric Hindrance

Steric hindrance refers to the prevention of reactions at a particular location within a molecule due to the size of substituent groups. In the context of 2,4,6-trimethylbenzoic acid, the three methyl groups create a crowded environment around the carboxylic acid functional group, making it difficult for the ethanol to approach and react, thus inhibiting ester formation.

Comparison of Reactivity

When comparing the reactivity of different carboxylic acids, the structure and substituents play a crucial role. The methyl ester of 4-methylbenzoic acid may have less steric hindrance than 2,4,6-trimethylbenzoic acid, potentially allowing for successful esterification with ethanol. Understanding how substituents affect reactivity is essential for predicting the outcomes of organic reactions.

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