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

DIBAL

Organic Chemistry

21. Aldehydes and Ketones: Nucleophilic Addition

DIBAL

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5:02 minutes

Problem 41

Textbook Question

When the ester attacked the aluminum of DIBAl-H, why did the carbonyl oxygen attack preferentially over the alkoxy oxygen?

Verified step by step guidance

Understand the structure of DIBAl-H: DIBAl-H stands for diisobutylaluminum hydride, which is a reducing agent commonly used in organic chemistry to reduce esters to aldehydes.

Identify the reactive sites in the ester: An ester has a carbonyl group (C=O) and an alkoxy group (OR). The carbonyl oxygen is more electronegative and has a partial negative charge, making it a potential site for nucleophilic attack.

Consider the mechanism of reduction: DIBAl-H is known to coordinate with the carbonyl oxygen due to its higher electronegativity compared to the alkoxy oxygen. This coordination is crucial for the reduction process.

Analyze the steric and electronic factors: The carbonyl oxygen is less hindered and more accessible for attack compared to the alkoxy oxygen, which is part of a larger group. Additionally, the carbonyl oxygen's lone pairs are more available for interaction with the aluminum.

Conclude why the carbonyl oxygen attacks preferentially: The combination of electronic factors (higher electronegativity and partial negative charge) and steric accessibility makes the carbonyl oxygen the preferred site for attack by the aluminum in DIBAl-H, facilitating the reduction of the ester to an aldehyde.

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Key Concepts

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

Nucleophilicity

Nucleophilicity refers to the ability of an atom or molecule to donate a pair of electrons to an electrophile, forming a chemical bond. In the context of the reaction with DIBAl-H, the carbonyl oxygen is more nucleophilic than the alkoxy oxygen due to its partial negative charge and the resonance stabilization of the carbonyl group, making it more reactive towards electrophilic centers like aluminum.

Electrophilic Centers

Electrophilic centers are atoms or regions in a molecule that are electron-deficient and can accept electron pairs from nucleophiles. In DIBAl-H, the aluminum atom is an electrophilic center due to its incomplete octet and positive charge, making it susceptible to attack by nucleophiles such as the carbonyl oxygen in esters.

Resonance Stabilization

Resonance stabilization occurs when a molecule can distribute its electron density over multiple structures, lowering its energy and increasing stability. In esters, the carbonyl group benefits from resonance, as the lone pair on the oxygen can delocalize into the carbon-oxygen double bond, enhancing the nucleophilicity of the carbonyl oxygen compared to the alkoxy oxygen, which lacks such stabilization.

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Related Practice

Textbook Question

Show how you would accomplish the following synthetic conversions efficiently and in good yield. You may use any necessary additional reagents and solvents.

(f)

Textbook Question

Show how you would accomplish the following synthetic conversions efficiently and in good yield. You may use any necessary additional reagents and solvents.

(c)

Textbook Question

Predict the major products of the following reactions.

(b)

Textbook Question

Predict the product of the following reaction sequences.

(b)

Textbook Question

The esters shown differ only by the alkoxy group.

(i) Predict the product(s) obtained when these react with DIBAl-H.

(ii) Based on your answer, in a sequence like this, would there ever be a need to convert from one ester to another?

(b)