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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2:46 minutes

Problem 35a

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.

Verified step by step guidance

Step 1: Understand the Diels–Alder reaction mechanism. The Diels–Alder reaction is a [4+2] cycloaddition reaction where a conjugated diene (furan) reacts with a dienophile (maleimide) to form a cyclic adduct. The reaction can produce two stereoisomers: the endo and exo products.

Step 2: Analyze the structures of furan and maleimide. Furan is a five-membered aromatic ring containing oxygen, and maleimide is a cyclic compound with a double bond and two carbonyl groups. Maleimide acts as the dienophile in this reaction.

Step 3: Draw the endo isomer. In the endo product, the substituents on the dienophile (the carbonyl groups of maleimide) are oriented towards the π-electron cloud of the diene (furan). This is due to secondary orbital interactions, which stabilize the endo product at lower temperatures.

Step 4: Draw the exo isomer. In the exo product, the substituents on the dienophile (the carbonyl groups of maleimide) are oriented away from the π-electron cloud of the diene. This isomer becomes the major product at higher temperatures due to thermodynamic stability.

Step 5: Label the structures. Clearly label the endo and exo isomers in your drawing. Indicate the orientation of the substituents (towards or away from the π-electron cloud) and ensure the cyclic adduct is correctly drawn to reflect the stereochemistry of the reaction.

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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 reaction between a 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 with high stereoselectivity. The reaction can yield different isomers, such as endo and exo, depending on the orientation of substituents in the product.

Stereochemistry: Endo vs. Exo

In the context of the Diels–Alder reaction, stereochemistry refers to the spatial arrangement of atoms in the resulting adduct. The endo isomer has substituents oriented towards the larger π system of the diene, while the exo isomer has them oriented away. This difference in orientation affects the stability and reactivity of the isomers, influencing which isomer predominates under specific conditions.

Isomerization

Isomerization is the process by which one isomer is transformed into another, often involving a change in the arrangement of atoms. In this case, the endo isomer of the Diels–Alder product can isomerize to the exo isomer at elevated temperatures, such as 90 °C. This thermal isomerization is crucial for understanding the stability and reactivity of the products formed in the reaction.

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Related Practice

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

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.)

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.

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

Textbook Question

Cyclopentadiene can react with itself in a Diels–Alder reaction. Draw the endo and exo products.

Textbook Question

Recall (Section 16-10) that two positions of anthracene sometimes react more like polyenes than like aromatic compounds.

b. The Diels–Alder reaction of anthracene with maleic anhydride is a common organic lab experiment. Predict the product of this Diels–Alder reaction.

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