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

Saponification

Organic Chemistry

22. Carboxylic Acid Derivatives: NAS

Saponification

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3:38 minutes

Problem 29

Textbook Question

D. N. Kursanov, a Russian chemist, proved that the bond that is broken in the hydroxide-ion-promoted hydrolysis of an ester is the acyl C—O bond, rather than the alkyl C—O bond, by studying the hydrolysis of the following ester under basic conditions:

a. What products contained the ¹⁸O label?
b. What product would have contained the ¹⁸O label if the alkyl C—O bond had broken?

Verified step by step guidance

Step 1: Analyze the ester structure provided in the image. The ester contains an acyl group (C=O) and an alkyl group (CH3CH2O). The oxygen labeled with O^18 is part of the alkyl group, specifically bonded to the carbon of the ethyl group.

Step 2: Understand the mechanism of hydroxide-ion-promoted hydrolysis of esters. In basic hydrolysis, the hydroxide ion attacks the carbonyl carbon of the acyl group, leading to the cleavage of the acyl C—O bond.

Step 3: Predict the products when the acyl C—O bond breaks. The reaction produces a carboxylate ion (CH3CH2COO^-) and an alcohol (CH3CH2O^18H). The O^18 label remains in the alcohol product because the acyl C—O bond is broken.

Step 4: Consider the alternative scenario where the alkyl C—O bond breaks. If this bond were to break, the products would be CH3CH2CO^18O^- (carboxylate ion with the O^18 label) and CH3CH2OH (regular alcohol without the O^18 label).

Step 5: Summarize the findings. When the acyl C—O bond breaks, the O^18 label is found in the alcohol product. If the alkyl C—O bond had broken, the O^18 label would have been found in the carboxylate ion product.

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Key Concepts

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

Ester Hydrolysis

Ester hydrolysis is a chemical reaction where an ester reacts with water to form an alcohol and a carboxylic acid. In the presence of a base, this reaction is often referred to as saponification. Understanding the mechanism of ester hydrolysis is crucial, as it involves breaking specific bonds within the ester, which can be influenced by the conditions of the reaction, such as the presence of hydroxide ions.

Bond Selectivity in Hydrolysis

In the hydrolysis of esters, the selectivity of bond cleavage is essential for determining the products formed. The acyl C—O bond is typically more susceptible to hydrolysis than the alkyl C—O bond under basic conditions. This concept is critical for understanding the experimental findings of Kursanov, as it explains why the O^18 label appears in specific products based on which bond is broken during the reaction.

Isotope Labeling

Isotope labeling involves using isotopes, such as O^18, to trace the movement of atoms through a chemical reaction. In the context of ester hydrolysis, the presence of the O^18 label in the products indicates which bond was broken during the reaction. This technique provides valuable insights into reaction mechanisms and helps chemists understand the pathways and transformations that occur during chemical processes.

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