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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4:32 minutes

Problem 33a

Textbook Question

Which of the following cyclic hemiacetals would you expect to have the highest K_eq for their formation? Explain your answer.
(a)

Verified step by step guidance

Identify the reactant and product in the given reaction. The reactant is a hydroxy aldehyde, and the product is a cyclic hemiacetal.

Understand that the formation of a cyclic hemiacetal involves the nucleophilic attack of the hydroxyl group on the carbonyl carbon, forming a new C-O bond and resulting in a ring structure.

Consider the size of the ring formed in the cyclic hemiacetal. Smaller rings, such as three-membered rings, are generally less stable due to angle strain.

Evaluate the stability of the cyclic hemiacetal. Five- and six-membered rings are typically more stable due to minimal angle strain and favorable enthalpic and entropic factors.

Conclude that the equilibrium constant (Keq) for the formation of a cyclic hemiacetal is higher when the resulting ring is more stable, typically favoring five- or six-membered rings over smaller rings.

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Key Concepts

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

Cyclic Hemiacetal Formation

Cyclic hemiacetals form when an alcohol group within a molecule reacts with an aldehyde or ketone group in the same molecule, creating a ring structure. This intramolecular reaction is favored when it results in a stable, five- or six-membered ring due to minimal ring strain and favorable enthalpic and entropic factors.

Equilibrium Constant (K_eq)

The equilibrium constant (K_eq) for a reaction quantifies the ratio of the concentration of products to reactants at equilibrium. A higher K_eq indicates that the products are favored at equilibrium, suggesting that the formation of the cyclic hemiacetal is more thermodynamically favorable compared to its open-chain form.

Ring Strain and Stability

Ring strain arises from bond angles deviating from their ideal values, torsional strain from eclipsing interactions, and steric strain from atoms being too close. Five- and six-membered rings are generally more stable due to minimal ring strain, making them more likely to form and persist, thus influencing the equilibrium position towards the cyclic form.

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