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

25. Condensation Chemistry

Conjugate Addition

Organic Chemistry

25. Condensation Chemistry

Conjugate Addition

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3:12 minutes

Problem 83

Textbook Question

A Cannizzaro reaction is the reaction of an aldehyde that has no a-hydrogens with concentrated aqueous sodium hydroxide. In this reaction, half the aldehyde is converted to a carboxylic acid and the other half is converted to an alcohol. Propose a mechanism for the following Cannizzaro reaction:

Verified step by step guidance

Step 1: Identify the key features of the reaction. The Cannizzaro reaction involves an aldehyde that lacks α-hydrogens reacting with concentrated sodium hydroxide. In this case, the aldehyde is 4-nitrobenzaldehyde, which lacks α-hydrogens due to the absence of hydrogens on the carbon adjacent to the carbonyl group.

Step 2: Initiate the reaction mechanism. The hydroxide ion (OH⁻) from the concentrated NaOH attacks the carbonyl carbon of the aldehyde, forming a tetrahedral intermediate. This step is nucleophilic addition.

Step 3: The tetrahedral intermediate undergoes rearrangement. One molecule of the aldehyde donates a hydride ion (H⁻) to another molecule of the aldehyde. This hydride transfer is the key step in the Cannizzaro reaction, leading to the formation of two distinct products.

Step 4: Formation of products. The molecule that receives the hydride ion is reduced to an alcohol (4-nitrobenzyl alcohol), while the molecule that donates the hydride ion is oxidized to a carboxylic acid (4-nitrobenzoate ion).

Step 5: Final step involves stabilization. The carboxylic acid product is deprotonated by the hydroxide ion in the basic medium, forming the carboxylate ion (4-nitrobenzoate ion). The alcohol product remains neutral.

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Key Concepts

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

Cannizzaro Reaction

The Cannizzaro reaction is a redox reaction that occurs with aldehydes lacking alpha-hydrogens when treated with a strong base, such as sodium hydroxide. In this reaction, one molecule of the aldehyde is oxidized to a carboxylic acid, while another molecule is reduced to an alcohol. This reaction is significant in organic chemistry as it provides a method for synthesizing both alcohols and carboxylic acids from simple aldehydes.

Mechanism of the Cannizzaro Reaction

The mechanism of the Cannizzaro reaction involves the formation of a hydride ion transfer between two aldehyde molecules. Initially, one aldehyde molecule is deprotonated by the base, forming an alkoxide ion. This alkoxide then attacks another aldehyde molecule, leading to the transfer of a hydride ion, resulting in the formation of a carboxylate ion and an alcohol. The carboxylate can then be protonated to yield the carboxylic acid.

Role of Sodium Hydroxide

Sodium hydroxide (NaOH) acts as a strong base in the Cannizzaro reaction, facilitating the deprotonation of the aldehyde. This step is crucial as it generates the alkoxide ion, which is a key intermediate in the reaction mechanism. The presence of concentrated NaOH not only drives the reaction forward but also helps stabilize the carboxylate ion formed during the process, allowing for the successful conversion of the aldehyde into both the carboxylic acid and the alcohol.

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