Skip to main content
Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet SpectroscopyProblem 35b
Chapter 15, Problem 35b

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.

Verified step by step guidance
1
Step 1: Understand the Diels–Alder reaction mechanism. The Diels–Alder reaction is a [4+2] cycloaddition between a conjugated diene (furan) and a dienophile (maleimide). This reaction forms a six-membered ring and is stereospecific, meaning the stereochemistry of the reactants influences the stereochemistry of the product.
Step 2: Analyze the endo and exo isomers. The endo isomer is typically favored in Diels–Alder reactions due to secondary orbital interactions. These interactions occur between the π-electrons of the diene and the π* orbitals of the dienophile, stabilizing the transition state and favoring the endo product.
Step 3: Consider the temperature effect. At 25 °C, the reaction is kinetically controlled, favoring the endo isomer due to the lower activation energy and stabilizing secondary orbital interactions. At 90 °C, the reaction becomes thermodynamically controlled, allowing the endo isomer to isomerize to the exo isomer, which is more stable due to steric factors.
Step 4: Explain why the endo isomer is usually favored. Under typical reaction conditions (lower temperatures), the endo isomer is favored because the reaction is kinetically controlled, and the secondary orbital interactions stabilize the transition state leading to the endo product.
Step 5: Summarize the findings. The endo isomer is the expected product under standard conditions due to kinetic control and secondary orbital interactions. However, at higher temperatures, the exo isomer becomes the major product due to thermodynamic control and its greater stability.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
5m
Was this helpful?

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 cycloaddition reaction between a conjugated diene and a dienophile, forming a six-membered ring. This reaction is a key method in organic synthesis due to its ability to create complex cyclic structures efficiently. The stereochemistry of the products can vary based on reaction conditions, such as temperature, which influences the stability of the resulting isomers.
Recommended video:
Guided course
04:02
Diels-Alder Retrosynthesis

Endo vs. Exo Isomers

In the context of the Diels–Alder reaction, endo and exo refer to the relative orientation of substituents on the newly formed ring. The endo isomer has substituents oriented towards the larger bridge of the bicyclic structure, while the exo isomer has them oriented away. Generally, the endo isomer is favored at lower temperatures due to secondary orbital interactions, while the exo isomer becomes more stable at higher temperatures.
Recommended video:
Guided course
01:10
What is a constitutional isomer?

Isomerization

Isomerization is the process by which one isomer is transformed into another, often involving the rearrangement of bonds. In the case of the Diels–Alder reaction, the endo isomer can isomerize to the exo isomer upon heating. This temperature-dependent behavior is crucial for understanding product distribution and stability, as the exo isomer is typically more thermodynamically stable at elevated temperatures.
Recommended video:
Guided course
06:47
Monosaccharides - D and L Isomerism
Related Practice
Textbook Question

Sketch the pi molecular orbitals of hexa-1,3,5-triene.

2539
views
Textbook Question

Show the electronic configuration of the ground state of hexa-1,3,5-triene.

1402
views
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.

897
views
Textbook Question

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

Part 1:

1351
views
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.

c. Examine your answer to (b) and determine whether this answer applies to a reaction that is kinetically controlled or one that is thermodynamically controlled, or both.

550
views
Textbook Question

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

Part 2:

1232
views