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

Robinson Annulation

Organic Chemistry

25. Condensation Chemistry

Robinson Annulation

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4:12 minutes

Problem 58a

Textbook Question

The base-catalyzed reaction of an aldehyde (having no α hydrogens) with an anhydride is called the Perkin condensation. Propose a mechanism for the following example of the Perkin condensation. (Sodium acetate serves as the base.)

Verified step by step guidance

Step 1: The reaction begins with the deprotonation of the anhydride by sodium acetate (CH₃CO₂Na), which acts as the base. This generates an enolate ion from the anhydride. The enolate ion is stabilized by resonance between the oxygen and the carbonyl group.

Step 2: The enolate ion then performs a nucleophilic attack on the carbonyl carbon of the aldehyde (benzaldehyde). This forms a tetrahedral intermediate, which subsequently collapses to eliminate acetate (CH₃CO₂⁻), regenerating the base.

Step 3: The resulting intermediate undergoes an aldol condensation. A proton is abstracted from the α-carbon of the intermediate, forming a new enolate ion. This enolate ion then eliminates a molecule of acetic acid (CH₃COOH), forming the α,β-unsaturated product.

Step 4: The reaction mixture is subjected to acidic workup (H₃O⁺), which ensures the protonation of any remaining intermediates and stabilizes the final product. This step also helps to isolate cinnamic acid as the major product.

Step 5: The final products of the reaction are cinnamic acid (an α,β-unsaturated carboxylic acid) and acetic acid (CH₃COOH). The mechanism highlights the role of sodium acetate as the base and the aldol condensation pathway in forming the conjugated double bond in cinnamic acid.

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Key Concepts

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

Perkin Condensation

The Perkin condensation is a reaction between an aldehyde and an anhydride, typically catalyzed by a base, to form α,β-unsaturated carboxylic acids. This reaction is significant in organic synthesis for constructing complex molecules. In this process, the aldehyde must lack α-hydrogens, which prevents self-condensation and allows for the formation of a specific product.

Mechanism of Base-Catalyzed Reactions

Base-catalyzed reactions involve the use of a base to facilitate the reaction by deprotonating a substrate, thereby increasing its nucleophilicity. In the context of the Perkin condensation, sodium acetate acts as the base, which helps in the formation of the nucleophile that attacks the anhydride. Understanding this mechanism is crucial for predicting the reaction pathway and the formation of intermediates.

Role of Sodium Acetate

Sodium acetate serves as a mild base in the Perkin condensation, promoting the reaction without overly aggressive conditions. It deprotonates the aldehyde, generating a more reactive enolate ion that can effectively attack the anhydride. This role is essential for the successful progression of the reaction and the formation of the desired α,β-unsaturated product.

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Related Practice

Textbook Question

Predict the product of the following reactions.

(b)

Textbook Question

Show how the following molecule might be synthesized using the Robinson annulation.

Textbook Question

Propose mechanisms for the following reactions.

(d)

Textbook Question

The base-catalyzed reaction of an aldehyde (having no α hydrogens) with an anhydride is called the Perkin condensation. Propose a mechanism for the following example of the Perkin condensation. (Sodium acetate serves as the base.)

Textbook Question

Show how you would use Robinson annulations to synthesize the following compounds. Work backward, remembering that the cyclohexenone is the new ring and that the double bond of the cyclohexenone is formed by the aldol with dehydration. Take apart the double bond, then see what structures the Michael donor and acceptor must have.

(a)

Textbook Question

(b)

Multiple Choice

Provide the product for the following Robinson Annulation Reaction.

Multiple Choice

How would you prepare the following compound using a Robinson annulation reaction between a di-ketone and an alpha, beta unsaturated ketone?

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