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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Multiple Choice

Why can't ester reduction with lithium aluminum hydride (LAH, LiAlH₄) stop at the aldehyde stage?

An aldehyde is inherently a more reactive functional group than an ester and will react preferentially over an ester when in competition.

The reaction with lithium aluminum hydride could stop at the aldehyde stage if the stoichiometry of the hydride reagent is carefully controlled.

The boiling point of the ester functional group is much higher than the boiling point of the corresponding aldehyde functional group.

The aldehyde functional group contains a good electron-donating group through resonance, causing the aldehyde to react faster.

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Verified step by step guidance

Begin by understanding the reactivity of esters and aldehydes. Esters are less reactive than aldehydes due to the presence of the electron-withdrawing alkoxy group, which stabilizes the ester and makes it less susceptible to nucleophilic attack.

Consider the mechanism of reduction with lithium aluminum hydride (LiAlH4). LiAlH4 is a strong reducing agent that donates hydride ions (H-) to the carbonyl carbon of the ester, leading to the formation of an aldehyde intermediate.

Recognize that aldehydes are more reactive than esters. Once the aldehyde is formed, it is more susceptible to further reduction by LiAlH4 because the carbonyl carbon in aldehydes is more electrophilic than in esters.

Understand that controlling the stoichiometry of LiAlH4 is challenging. Even if theoretically possible, in practice, it is difficult to stop the reaction at the aldehyde stage because any excess LiAlH4 will continue to reduce the aldehyde to a primary alcohol.

Note that the boiling point and resonance effects mentioned in the problem are not the primary reasons for the inability to stop at the aldehyde stage. The key factor is the inherent reactivity difference between aldehydes and esters, with aldehydes reacting preferentially due to their higher electrophilicity.