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

Claisen Condensation

Organic Chemistry

25. Condensation Chemistry

Claisen Condensation

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Problem 41

Textbook Question

Propose a mechanism for the crossed Claisen condensation between ethyl acetate and ethyl benzoate.

Verified step by step guidance

Step 1: Identify the reactants and the type of reaction. The crossed Claisen condensation involves two esters, ethyl acetate (CH₃COOCH₂CH₃) and ethyl benzoate (C₆H₅COOCH₂CH₃), reacting in the presence of a strong base to form a β-keto ester.

Step 2: Deprotonation of the α-hydrogen. A strong base, such as sodium ethoxide (NaOCH₂CH₃), deprotonates the α-hydrogen of ethyl acetate, forming an enolate ion. The enolate ion is stabilized by resonance, with the negative charge delocalized between the oxygen atom and the α-carbon.

Step 3: Nucleophilic attack of the enolate ion. The enolate ion acts as a nucleophile and attacks the carbonyl carbon of ethyl benzoate. This step forms a tetrahedral intermediate, where the negative charge is temporarily localized on the oxygen atom of the carbonyl group.

Step 4: Collapse of the tetrahedral intermediate. The tetrahedral intermediate collapses, expelling the ethoxide ion (CH₃CH₂O⁻) as a leaving group. This step results in the formation of a β-keto ester, where the two original esters are now connected through a new carbon-carbon bond.

Step 5: Protonation of the product. The β-keto ester formed in the previous step is protonated by the solvent or another proton source, stabilizing the final product. The reaction is complete, yielding the crossed Claisen condensation product.

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Key Concepts

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

Claisen Condensation

Claisen condensation is a reaction between two esters or an ester and a carbonyl compound in the presence of a strong base, leading to the formation of a β-keto ester or a β-diketone. This reaction involves the nucleophilic attack of an enolate ion, generated from one of the esters, on the carbonyl carbon of the other ester. Understanding this mechanism is crucial for proposing the crossed Claisen condensation between ethyl acetate and ethyl benzoate.

Enolate Ion Formation

Enolate ions are formed when a strong base abstracts a proton from the α-carbon of an ester or carbonyl compound, resulting in a resonance-stabilized anion. This enolate ion acts as a nucleophile in the Claisen condensation, attacking the electrophilic carbonyl carbon of another ester. Recognizing how enolate ions are generated and their role in nucleophilic attacks is essential for understanding the mechanism of the crossed Claisen condensation.

Crossed Claisen Condensation

Crossed Claisen condensation refers to the reaction between two different esters or an ester and a carbonyl compound, which can lead to the formation of a new carbon-carbon bond. This reaction is selective and can yield different products depending on the choice of reactants and the conditions used. Analyzing the specific reactants, such as ethyl acetate and ethyl benzoate, is vital for predicting the outcome and mechanism of the reaction.

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