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

Cyanohydrin

Organic Chemistry

21. Aldehydes and Ketones: Nucleophilic Addition

Cyanohydrin

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2:38 minutes

Problem 15

Textbook Question

Propose a mechanism for each cyanohydrin synthesis just shown.

Verified step by step guidance

Step 1: Identify the starting material and the reagent. In each case, the starting material is either an aldehyde or a ketone, and the reagent is hydrogen cyanide (HCN). The reaction is catalyzed by cyanide ions (CN⁻).

Step 2: Understand the mechanism. The cyanohydrin synthesis involves nucleophilic addition of the cyanide ion (CN⁻) to the carbonyl group (C=O) of the aldehyde or ketone. This is followed by protonation of the resulting alkoxide intermediate.

Step 3: Initiate the reaction. The cyanide ion (CN⁻) attacks the electrophilic carbon atom of the carbonyl group, breaking the π bond and forming a tetrahedral intermediate. Represent this step as:

C_{1} (C = O) + {CN}_{-} \to C_{1} (C - O - {CN}_{-})

Step 4: Protonation of the intermediate. The negatively charged oxygen atom in the tetrahedral intermediate is protonated by HCN, forming the cyanohydrin product. Represent this step as:

C_{1} (C - O - {CN}_{-}) + HCN \to C_{1} (C - OH - {CN}_{-})

Step 5: Analyze the steric and electronic effects. The yield of cyanohydrin depends on the steric hindrance around the carbonyl group. For propanal, the reaction proceeds efficiently due to minimal steric hindrance. For butan-2-one, the yield is slightly lower due to increased steric hindrance. For di-tert-butylketone, the reaction is slow and yields are poor due to significant steric hindrance around the carbonyl group.

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Key Concepts

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

Cyanohydrin Formation

Cyanohydrins are formed through the nucleophilic addition of hydrogen cyanide (HCN) to carbonyl compounds, such as aldehydes or ketones. In this reaction, the nucleophile (cyanide ion) attacks the electrophilic carbon of the carbonyl group, leading to the formation of a hydroxyl group and a cyano group on the same carbon atom.

Nucleophilic Addition Mechanism

The nucleophilic addition mechanism involves the attack of a nucleophile on an electrophile, resulting in the formation of a new bond. In the case of cyanohydrin synthesis, the cyanide ion acts as the nucleophile, while the carbonyl carbon serves as the electrophile. This mechanism typically includes a tetrahedral intermediate before the final product is formed.

Stereochemistry of Cyanohydrins

Cyanohydrins can exhibit stereochemistry due to the presence of a chiral center formed during their synthesis. The addition of HCN to the carbonyl carbon can lead to the formation of two enantiomers, depending on the orientation of the nucleophile's attack. Understanding the stereochemical implications is crucial for predicting the properties and reactivity of the resulting cyanohydrins.

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