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

21. Aldehydes and Ketones: Nucleophilic Addition

Hemiacetal

Organic Chemistry

21. Aldehydes and Ketones: Nucleophilic Addition

Hemiacetal

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2:48 minutes

Problem 32a

Textbook Question

Provide a mechanism for the formation of the hemiacetals shown. [Only (c) is favored as written.]
(a)

Verified step by step guidance

Identify the reactants involved in the formation of a hemiacetal. Typically, a hemiacetal is formed from an aldehyde or ketone reacting with an alcohol.

Recognize the functional groups present in the reactants. The carbonyl group (C=O) in the aldehyde or ketone is the electrophile, while the hydroxyl group (OH) in the alcohol acts as the nucleophile.

Initiate the mechanism by protonating the carbonyl oxygen to make the carbonyl carbon more electrophilic. This is often facilitated by an acid catalyst.

The nucleophilic attack occurs when the alcohol's oxygen atom donates a pair of electrons to the electrophilic carbonyl carbon, forming a new C-O bond.

Complete the mechanism by deprotonating the oxygen atom of the alcohol, resulting in the formation of the hemiacetal. The structure now contains both an alcohol and an ether functional group on the same carbon.

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Key Concepts

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

Hemiacetal Formation

Hemiacetals are formed when an alcohol reacts with an aldehyde or ketone. This reaction involves the nucleophilic attack of the alcohol's hydroxyl group on the carbonyl carbon, leading to the formation of a tetrahedral intermediate. The subsequent proton transfer and loss of water yield the hemiacetal, which contains both an alcohol and an ether functional group.

Equilibrium and Favorability

The formation of hemiacetals is an equilibrium process, meaning that both the reactants and products can coexist. The position of this equilibrium can be influenced by factors such as concentration, temperature, and the nature of the reactants. In the context of the question, understanding which hemiacetal is favored requires analyzing these factors and the stability of the resulting structures.

Mechanistic Steps

The mechanism for hemiacetal formation involves several key steps: nucleophilic attack, formation of a tetrahedral intermediate, proton transfer, and elimination of water. Each step is crucial for understanding how the reaction proceeds and how the structure of the hemiacetal is established. A clear grasp of these mechanistic steps is essential for predicting the outcome of the reaction and the stability of the products.

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