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

16. Conjugated Systems

Diels-Alder Forming Bridged Products

Organic Chemistry

16. Conjugated Systems

Diels-Alder Forming Bridged Products

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2:21 minutes

Problem 29b

Textbook Question

The diene lactone shown in part (a) has one electron-donating group (-OR) and one electron-withdrawing group (C=O). This diene lactone is sufficiently electron-rich to serve as the diene in a Diels–Alder reaction.

b. The Diels–Alder product A is not very stable. Upon mild heating, it reacts to produce CO₂ gas and methyl benzoate (PhCOOCH₃), a very stable product. Explain how this strongly exothermic decarboxylation takes place. (Hint: Under the right conditions, the Diels–Alder reaction can be reversible.)

Verified step by step guidance

Step 1: Analyze the diene lactone structure. The diene lactone contains a conjugated diene system with one electron-donating group (-OR) and one electron-withdrawing group (C=O). These groups influence the electron density of the diene, making it electron-rich and suitable for a Diels–Alder reaction with an electron-deficient dienophile.

Step 2: Examine the dienophile, methyl acetylene carboxylate. This molecule contains a triple bond (C≡C) and an electron-withdrawing ester group (-COOCH3), making it electron-deficient and reactive toward the electron-rich diene lactone in the Diels–Alder reaction.

Step 3: Describe the Diels–Alder reaction mechanism. The diene lactone reacts with the dienophile to form a cyclic adduct (product A). This reaction involves a [4+2] cycloaddition, where the diene contributes four π-electrons and the dienophile contributes two π-electrons to form a new six-membered ring.

Step 4: Explain the instability of product A. Product A is unstable due to strain in the newly formed ring and the presence of functional groups that can undergo further reactions. Upon mild heating, product A undergoes a retro-Diels–Alder reaction, releasing CO2 gas and forming methyl benzoate (PhCOOCH3).

Step 5: Discuss the decarboxylation process. The retro-Diels–Alder reaction is strongly exothermic because it releases CO2, a stable gas, and forms methyl benzoate, a thermodynamically stable aromatic compound. This drives the reaction forward under mild heating conditions.

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Key Concepts

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

Diels–Alder Reaction

The Diels–Alder reaction is a [4+2] cycloaddition between a conjugated diene and a dienophile, forming a six-membered ring. This reaction is significant in organic synthesis due to its ability to create complex cyclic structures in a single step. The electron-rich diene and electron-poor dienophile interact to form a new sigma bond, making it a valuable tool for constructing various organic compounds.

Decarboxylation

Decarboxylation is the process of removing a carboxyl group (-COOH) from a molecule, resulting in the release of carbon dioxide (CO2). This reaction often occurs in organic compounds under heat or catalytic conditions, leading to more stable products. In the context of the Diels–Alder product, decarboxylation can enhance stability by converting a less stable intermediate into a more stable compound, such as methyl benzoate.

Reversibility of Diels–Alder Reaction

The Diels–Alder reaction can be reversible under certain conditions, particularly when the reaction is conducted at elevated temperatures or when the products are less stable. This reversibility allows the reaction to shift back to the reactants, facilitating the formation of more stable products through subsequent reactions, such as decarboxylation. Understanding this concept is crucial for predicting the behavior of Diels–Alder adducts in various chemical environments.

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Related Practice

Textbook Question

Predict the major product for each proposed Diels–Alder reaction. Include stereochemistry where appropriate.

(a)

Textbook Question

Predict the products of the following Diels–Alder reactions.

(a)

(b)

Textbook Question

Predict the products of the following proposed Diels–Alder reactions. Include stereochemistry where appropriate.

(a)

(b)

(c)

Textbook Question

Give the structures of the products represented by letters in this synthesis.

Part 3:

Textbook Question

Predict the products of the following reactions.

(h) cyclopentadiene + methyl acrylate, CH₂=CH–COOCH₃

Textbook Question

Furan and maleimide undergo a Diels–Alder reaction at 25 °C to give the endo isomer of the product. When the reaction takes place at 90 °C, however, the major product is the exo isomer. Further study shows that the endo isomer of the product isomerizes to the exo isomer at 90 °C.

a. Draw and label the endo and exo isomers of the Diels–Alder adduct of furan and maleimide.

Textbook Question

b. Which isomer of the product would you usually expect from this reaction? Explain why this isomer is usually favored.

Textbook Question

1,4-Benzoquinone is a good Diels–Alder dienophile. Predict the products of its reaction with

a. buta-1,3-diene

b. cyclopenta-1,3-diene

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