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

Ketone and Aldehyde Synthesis Reactions

Organic Chemistry

21. Aldehydes and Ketones: Nucleophilic Addition

Ketone and Aldehyde Synthesis Reactions

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3:46 minutes

Problem 27

Textbook Question

In the mechanism for acetal hydrolysis shown, the ring oxygen atom was protonated first, the ring was cleaved, and then the methoxy group was lost. The mechanism could also be written to show the methoxy oxygen protonating and cleaving first, followed by ring cleavage. Draw this alternative mechanism.

Verified step by step guidance

Identify the starting structure of the acetal and recognize the functional groups involved. Acetals typically have two alkoxy groups (-OR) attached to the same carbon atom, and in this case, one of the alkoxy groups is part of a ring structure.

Protonate the methoxy oxygen atom first. This step involves the addition of a proton (H⁺) to the methoxy oxygen, making it a better leaving group. Represent this step using curved arrows to show the movement of electrons from the oxygen lone pair to the proton.

Facilitate the cleavage of the methoxy group. After protonation, the methoxy group becomes a good leaving group and departs, forming a carbocation intermediate. Use curved arrows to show the bond breaking between the carbon and the methoxy group.

Protonate the ring oxygen atom. Once the methoxy group has left, the ring oxygen atom can be protonated by another molecule of acid (H⁺), making it more electrophilic and susceptible to cleavage.

Cleave the ring structure. After protonation, the bond between the ring oxygen and the adjacent carbon is broken, leading to the formation of a second carbocation intermediate and the release of the ring oxygen as a neutral molecule. Use curved arrows to show the bond breaking and electron movement.

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Key Concepts

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

Acetal Hydrolysis

Acetal hydrolysis is a chemical reaction where an acetal is converted back into its corresponding carbonyl compound and alcohol in the presence of water, typically under acidic conditions. This process involves the protonation of the acetal oxygen, leading to the cleavage of the carbon-oxygen bond and the formation of a hemiacetal intermediate before yielding the final products.

Protonation

Protonation is the addition of a proton (H+) to a molecule, which often enhances its reactivity. In the context of acetal hydrolysis, protonation of the oxygen atom in the acetal increases the electrophilicity of the carbon atom, facilitating the cleavage of the ring and the subsequent loss of the methoxy group.

Reaction Mechanism

A reaction mechanism is a step-by-step description of the pathway by which reactants are converted into products. Understanding the mechanism of acetal hydrolysis is crucial, as it allows chemists to visualize the sequence of protonation, bond cleavage, and rearrangement, which can vary depending on the order of events, such as whether the methoxy group or the ring oxygen is protonated first.

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