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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3:41 minutes

Problem 65c

Textbook Question

There are other condensation reactions similar to the aldol and Claisen condensations:
c. The Knoevenagel condensation is the condensation of an aldehyde or a ketone that has no a-hydrogens and a compound such as diethyl malonate that has an a-carbon flanked by two electron-withdrawing groups. Draw the product obtained from the following Knoevenagel condensation:

Verified step by step guidance

Step 1: Identify the reactants in the Knoevenagel condensation. The first reactant is an aldehyde or ketone without α-hydrogens, which in this case is the aromatic ketone (4-methylbenzophenone). The second reactant is diethyl malonate, which has an α-carbon flanked by two electron-withdrawing groups (the ester groups). The base used is sodium ethoxide (EtONa).

Step 2: Deprotonation of the α-carbon in diethyl malonate occurs due to the presence of the strong base (EtONa). This generates a resonance-stabilized enolate ion. The enolate ion is nucleophilic and will attack the electrophilic carbonyl carbon of the ketone.

Step 3: The nucleophilic enolate ion attacks the carbonyl carbon of the ketone, forming a new carbon-carbon bond. This step results in the formation of a β-hydroxy intermediate.

Step 4: Under the reaction conditions, the β-hydroxy intermediate undergoes dehydration (loss of water) to form a conjugated double bond. This elimination step leads to the formation of an α,β-unsaturated product.

Step 5: The final product is a conjugated system where the diethyl malonate has condensed with the ketone, forming a compound with a double bond between the α-carbon of diethyl malonate and the carbonyl carbon of the ketone. The electron-withdrawing ester groups stabilize the conjugated system.

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Key Concepts

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

Knoevenagel Condensation

The Knoevenagel condensation is a reaction between an aldehyde or a ketone lacking alpha-hydrogens and a compound with an active methylene group, typically flanked by electron-withdrawing groups. This reaction results in the formation of a β-unsaturated carbonyl compound through the elimination of water. It is a key method for synthesizing enones and enals, which are important intermediates in organic synthesis.

Active Methylene Group

An active methylene group refers to a methylene (-CH2-) group that is adjacent to two electron-withdrawing groups, making it highly acidic and reactive. This acidity allows for the deprotonation of the methylene hydrogen, facilitating nucleophilic attack on electrophiles, such as carbonyl compounds in condensation reactions. In the context of the Knoevenagel condensation, this group is essential for forming the new carbon-carbon bond.

Electron-Withdrawing Groups

Electron-withdrawing groups (EWGs) are substituents that pull electron density away from the rest of the molecule, stabilizing negative charges and increasing the electrophilicity of nearby carbonyl groups. Common examples include nitro (-NO2), cyano (-CN), and carbonyl (-C=O) groups. In the Knoevenagel condensation, the presence of EWGs enhances the reactivity of the active methylene compound, making it more likely to participate in the reaction.

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Related Practice

Textbook Question

Show how Claisen condensations could be used to make the following compounds.

(d)

Textbook Question

Predict the products of the following Claisen condensations.

(a)

(b)

Textbook Question

There are other condensation reactions similar to the aldol and Claisen condensations:

a. The Perkin condensation is the condensation of an aromatic aldehyde and acetic anhydride. Draw the product obtained from the following Perkin condensation:

Textbook Question

What product is obtained when the product of a Knoevenagel condensation is heated in an aqueous acidic solution?

Textbook Question

The Knoevenagel condensation is a special case of the aldol condensation in which an active methylene compound reacts with an aldehyde or ketone, in the presence of a secondary amine as a basic catalyst, to produce a new C=C. Show the starting materials that made each of these by a Knoevenagel condensation.

(a)

Textbook Question

Show how you would use an aldol, Claisen, or another type of condensation to make each compound.

(a)

Textbook Question

Propose mechanisms for the reactions shown in Problems 22-63 part (b).

Textbook Question

Show how you would use an aldol, Claisen, or another type of condensation to make each compound.

(f)

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