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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2:12 minutes

Problem 42c,d

Textbook Question

Predict the products from crossed Claisen condensation of the following pairs of esters. Indicate which combinations are poor choices for crossed Claisen condensations.
(c)
(d)

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Identify the esters involved in the crossed Claisen condensation. In a crossed Claisen condensation, two different esters react in the presence of a strong base to form a β-keto ester.

Determine the enolate ion that will form from each ester. The enolate ion is generated from the ester with the more acidic alpha hydrogen. Use the base to deprotonate the alpha hydrogen of the ester to form the enolate ion.

Consider the reactivity of each ester. Esters with no alpha hydrogens cannot form enolates and will act as electrophiles. Identify which ester will act as the nucleophile (enolate) and which will act as the electrophile.

Predict the product by combining the enolate ion with the carbonyl carbon of the electrophilic ester. This forms a new carbon-carbon bond, resulting in a β-keto ester.

Evaluate the choice of esters for the reaction. A poor choice for crossed Claisen condensation occurs when both esters can form enolates, leading to a mixture of products. Ideally, one ester should lack alpha hydrogens to avoid multiple products.

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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 derived from one ester on the carbonyl carbon of another ester, followed by the elimination of an alcohol. Understanding this mechanism is crucial for predicting the products of crossed Claisen condensations.

Enolate Ion Formation

Enolate ions are formed when a strong base abstracts a proton from the α-carbon of an ester, resulting in a resonance-stabilized anion. The stability of the enolate ion is influenced by the substituents on the ester, which can affect the reactivity in the Claisen condensation. Recognizing how to generate and utilize enolate ions is essential for successfully predicting the outcomes of crossed Claisen reactions.

Crossed Claisen Condensation Limitations

Crossed Claisen condensation can lead to multiple products, especially when using two different esters. Poor choices for this reaction typically involve esters that can both form enolates, leading to self-condensation rather than the desired crossed product. Identifying which ester combinations are likely to yield unwanted products is key to successfully predicting the outcomes of these reactions.

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Related Practice

Textbook Question

Ethoxide is used as the base in the condensation of ethyl acetate to avoid some unwanted side reactions. Show what side reactions would occur if the following bases were used.

(a) sodium methoxide

(b) sodium hydroxide

Textbook Question

Esters with only one α hydrogen generally give poor yields in the Claisen condensation. Propose a mechanism for the Claisen condensation of ethyl isobutyrate, and explain why a poor yield is obtained.

Textbook Question

Predict the products of self-condensation of the following esters.

(a) methyl propanoate + NaOCH₃

(b) ethyl phenylacetate + NaOCH2CH₃

Textbook Question

Predict the products from crossed Claisen condensation of the following pairs of esters. Indicate which combinations are poor choices for crossed Claisen condensations.

(a)

(b)

Textbook Question

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

(d)

Textbook Question

Write the mechanism for the reaction of a 1,7-diester with an alkoxide ion to form a cyclic b-keto ester.

Textbook Question

Draw the products of the following reactions:

d. diethyl 1,2-benzenedicarboxylate + sodium ethoxide: (1) slow addition of ethyl acetate; (2) HCl

Textbook Question

Show how crossed Claisen condensations could be used to prepare the following esters.

(a)

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Predict the products from crossed Claisen condensation of the following pairs of esters. Indicate which combinations are poor choices for crossed Claisen condensations.(c) (d)

Key Concepts

Claisen Condensation

Enolate Ion Formation

Crossed Claisen Condensation Limitations

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Predict the products from crossed Claisen condensation of the following pairs of esters. Indicate which combinations are poor choices for crossed Claisen condensations.
(c)
(d)