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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6:40 minutes

Problem 24a

Textbook Question

Predict the products of aldol condensation, followed by dehydration, of the following ketones and aldehydes.
(a) butyraldehyde

Verified step by step guidance

Identify the reactants: Butyraldehyde (CH₃CH₂CH₂CHO) is an aldehyde with an alpha-hydrogen, making it capable of undergoing aldol condensation.

Determine the enolate formation: In the presence of a base (e.g., OH⁻), the alpha-hydrogen of butyraldehyde is abstracted, forming an enolate ion. The enolate ion is a nucleophile.

Perform the aldol addition: The enolate ion attacks the carbonyl carbon of another butyraldehyde molecule, forming a β-hydroxyaldehyde intermediate. The structure of this intermediate is CH₃CH₂CH(OH)CH₂CHO.

Carry out the dehydration step: Under heating or in the presence of a strong base, the β-hydroxyaldehyde undergoes elimination of water (dehydration) to form an α,β-unsaturated aldehyde. The product is crotonaldehyde (CH₃CH=CHCHO).

Summarize the reaction: The overall reaction involves the formation of crotonaldehyde as the final product through aldol condensation and subsequent dehydration of butyraldehyde.

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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 at least one alpha-hydrogen. In this process, one molecule acts as a nucleophile and attacks the carbonyl carbon of another molecule, forming a beta-hydroxy aldehyde or ketone. This intermediate can then undergo dehydration to yield an α,β-unsaturated carbonyl compound, which is often the final product of the reaction.

Dehydration Reaction

Dehydration is the process of removing a water molecule from a compound. In the context of aldol condensation, after the formation of the beta-hydroxy carbonyl compound, dehydration occurs, leading to the formation of a double bond between the alpha and beta carbons. This step is crucial as it stabilizes the product and enhances its reactivity, often resulting in conjugated systems that are more favorable in organic reactions.

Alpha-Hydrogen

Alpha-hydrogens are the hydrogen atoms attached to the carbon atom adjacent to a carbonyl group (C=O) in aldehydes and ketones. The presence of alpha-hydrogens is essential for aldol condensation, as they can be abstracted by a base to form an enolate ion, which is a key intermediate in the reaction. The ability to form enolates is what allows these compounds to participate in nucleophilic addition reactions.

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Textbook Question

The following compounds can be synthesized by aldol condensations, followed by further reactions. (In each case, work backward from the target molecule to an aldol product, and show what compounds are needed for the condensation.)

(b)

Textbook Question

(a)

Textbook Question

Predict the products of aldol condensation, followed by dehydration, of the following ketones and aldehydes.

Textbook Question

Predict the products of aldol condensation, followed by dehydration, of the following ketones and aldehydes.

(b) acetophenone

Textbook Question

Give the expected products for the aldol condensations of (c) pentan-3-one.

Textbook Question

Give the expected products for the aldol condensations of (b) phenylacetaldehyde.

Textbook Question

Give the expected products for the aldol condensations of (a) propanal.

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)

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Predict the products of aldol condensation, followed by dehydration, of the following ketones and aldehydes. (a) butyraldehyde

Key Concepts

Aldol Condensation

Dehydration Reaction

Alpha-Hydrogen

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Predict the products of aldol condensation, followed by dehydration, of the following ketones and aldehydes.
(a) butyraldehyde