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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5:05 minutes

Problem 22a,b

Textbook Question

Propose a mechanism for the dehydration of diacetone alcohol to mesityl oxide
(a) in acid.
(b) in base.

Verified step by step guidance

Step 1: (Acidic conditions) Begin by protonating the hydroxyl group (-OH) of diacetone alcohol using the acid catalyst. This increases the electrophilicity of the oxygen atom and makes the molecule more susceptible to elimination.

Step 2: (Acidic conditions) After protonation, the molecule undergoes an E1 elimination mechanism. The protonated hydroxyl group leaves as water (H₂O), forming a carbocation intermediate.

Step 3: (Acidic conditions) The carbocation intermediate undergoes rearrangement or stabilization, if necessary, and a proton is removed from the adjacent carbon atom (α-carbon) by the conjugate base of the acid. This results in the formation of a double bond, yielding mesityl oxide.

Step 4: (Basic conditions) In basic conditions, the base abstracts a proton from the α-carbon adjacent to the hydroxyl group of diacetone alcohol, forming an enolate ion. This step initiates the E2 elimination mechanism.

Step 5: (Basic conditions) The enolate ion facilitates the elimination of the hydroxyl group (-OH) as water (H₂O), forming a double bond between the α-carbon and β-carbon, resulting in mesityl oxide.

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Key Concepts

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

Dehydration Reaction

Dehydration reactions involve the removal of a water molecule from a compound, often resulting in the formation of a double bond. In organic chemistry, this process is crucial for converting alcohols into alkenes or other unsaturated compounds. Understanding the conditions under which dehydration occurs, such as acidic or basic environments, is essential for predicting the products and mechanisms involved.

Acid-Catalyzed Mechanism

In acid-catalyzed dehydration, the alcohol is protonated by an acid, increasing its electrophilicity. This leads to the formation of a carbocation intermediate, which can then lose a water molecule to form a double bond. The stability of the carbocation and the ability to rearrange can significantly influence the reaction pathway and the final product, such as mesityl oxide in this case.

Base-Catalyzed Mechanism

In base-catalyzed dehydration, a base abstracts a proton from the alcohol, generating an alkoxide ion that can eliminate a water molecule. This mechanism typically involves a concerted process where the bond formation and bond breaking occur simultaneously, leading to the formation of an alkene. The choice of base and the reaction conditions can affect the efficiency and selectivity of the dehydration process.

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Related Practice

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.

(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

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

(a)

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)

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.

(c)

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Propose a mechanism for the dehydration of diacetone alcohol to mesityl oxide(a) in acid.(b) in base.

Key Concepts

Dehydration Reaction

Acid-Catalyzed Mechanism

Base-Catalyzed Mechanism

Watch next

Propose a mechanism for the dehydration of diacetone alcohol to mesityl oxide
(a) in acid.
(b) in base.