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

Aldol Condensation

Organic Chemistry

25. Condensation Chemistry

Aldol Condensation

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7:56 minutes

Problem 62a

Textbook Question

Predict the products of the following aldol condensations. Show the products both before and after dehydration.
(a)

Verified step by step guidance

Step 1: Identify the reactants and the type of reaction. The given reaction involves an aldol condensation, which typically occurs between an aldehyde or ketone with an α-hydrogen in the presence of a base (here, -OH). The reactant is isobutyraldehyde (CH3)2CHCH2CHO.

Step 2: Determine the enolate formation. In the presence of a base, the α-hydrogen (hydrogen attached to the carbon adjacent to the carbonyl group) is abstracted, forming an enolate ion. The enolate ion is resonance-stabilized, with the negative charge delocalized between the α-carbon and the oxygen of the carbonyl group.

Step 3: Perform the nucleophilic attack. The enolate ion acts as a nucleophile and attacks the carbonyl carbon of another molecule of isobutyraldehyde. This forms a β-hydroxyaldehyde intermediate, which is the product before dehydration.

Step 4: Dehydration step. Under the reaction conditions, the β-hydroxyaldehyde undergoes dehydration (loss of water) to form an α,β-unsaturated aldehyde. This step involves the elimination of a hydroxyl group (-OH) and a hydrogen atom from the β-carbon and α-carbon, respectively, resulting in the formation of a double bond between the α- and β-carbons.

Step 5: Write the final products. The product before dehydration is the β-hydroxyaldehyde, and the product after dehydration is the α,β-unsaturated aldehyde. Ensure the chemical structures are drawn correctly to reflect these transformations.

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Key Concepts

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

Aldol Condensation

Aldol condensation is a reaction between aldehydes or ketones that contain alpha-hydrogens, leading to the formation of β-hydroxy aldehydes or ketones. This reaction involves the nucleophilic addition of an enolate ion to a carbonyl compound, followed by dehydration to yield an α,β-unsaturated carbonyl compound. Understanding this process is crucial for predicting the products of the reaction.

Enolate Ion Formation

Enolate ions are formed when a base abstracts an alpha-hydrogen from a carbonyl compound, resulting in a resonance-stabilized anion. This ion acts as a nucleophile in aldol reactions, attacking the carbonyl carbon of another molecule. Recognizing how enolate ions are generated and their role in the reaction mechanism is essential for predicting the products of aldol condensations.

Dehydration Step

The dehydration step in aldol condensation involves the elimination of a water molecule from the β-hydroxy carbonyl compound, resulting in the formation of an α,β-unsaturated carbonyl compound. This step is driven by the stability of the resulting double bond and is crucial for completing the reaction. Understanding this step helps in identifying the final products of the aldol condensation process.

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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.

(b)

Textbook Question

(c)

Textbook Question

Propose a mechanism for the aldol condensation of cyclohexanone. Do you expect the equilibrium to favor the reactant or the product?

Textbook Question

Propose a complete mechanism for the acid-catalyzed aldol condensation of acetone.

Textbook Question

Propose a mechanism for the dehydration of diacetone alcohol to mesityl oxide

(a) in acid.

(b) in base.

Textbook Question

Show how each compound can be dissected into reagents joined by an aldol condensation, then decide whether the necessary aldol condensation is feasible.

(a)

Textbook Question

Using cyclopentanone as the reactant, show the product of

b. an aldol addition.

c. an aldol condensation.

Textbook Question

Show how each compound can be dissected into reagents joined by an aldol condensation, then decide whether the necessary aldol condensation is feasible.

(b)

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Predict the products of the following aldol condensations. Show the products both before and after dehydration.(a)

Key Concepts

Aldol Condensation

Enolate Ion Formation

Dehydration Step

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Predict the products of the following aldol condensations. Show the products both before and after dehydration.
(a)