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 Reaction

Organic Chemistry

16. Conjugated Systems

Diels-Alder Reaction

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7:22 minutes

Problem 17a,b

Textbook Question

We predicted that the products would have a 1,2- or 1,4-relationship of the proper substituents. Draw the charge-separated resonance forms of the reactants to support these predictions.
(a) (b)

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Identify the reactants in each image. In the first image, the reactants are isoprene (2-methyl-1,3-butadiene) and methyl vinyl ketone. In the second image, the reactants are methoxybutadiene and acrylonitrile.

For each pair of reactants, consider the possibility of a Diels-Alder reaction, which involves a diene and a dienophile. The diene is the compound with two double bonds, and the dienophile is the compound with one double bond and an electron-withdrawing group.

Draw the resonance structures for the diene and the dienophile. For the diene, show the movement of electrons to form a charge-separated structure. For the dienophile, show the electron-withdrawing group stabilizing the negative charge.

For the first pair, isoprene can form a resonance structure where one of the double bonds shifts, creating a positive charge on one carbon and a negative charge on another. Methyl vinyl ketone can form a resonance structure where the carbonyl group stabilizes a negative charge.

For the second pair, methoxybutadiene can form a resonance structure with a positive charge on the carbon adjacent to the methoxy group and a negative charge on the terminal carbon. Acrylonitrile can form a resonance structure where the cyano group stabilizes a negative charge.

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Key Concepts

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

Resonance Structures

Resonance structures are different ways of drawing the same molecule that illustrate the delocalization of electrons. They help in understanding the distribution of charge and the stability of a molecule. In organic chemistry, resonance is crucial for predicting the behavior of reactants and products, especially in reactions involving conjugated systems.

Charge Separation

Charge separation refers to the distribution of positive and negative charges within a molecule. In resonance forms, charge separation can indicate the stability of a compound; structures with minimized charge separation are generally more stable. Understanding charge separation is essential for predicting the reactivity and product formation in organic reactions.

Substituent Positioning

The positioning of substituents on a molecule significantly influences its chemical properties and reactivity. In the context of the question, the 1,2- and 1,4-relationships refer to the relative positions of substituents on a benzene ring or similar structure. Recognizing these relationships is vital for predicting the outcomes of reactions and understanding the stability of the resulting products.

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Related Practice

Textbook Question

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

(e)

(f)

Textbook Question

An important variation of the Diels–Alder reaction is intramolecular, in which the diene and the dienophile are connected. This type of Diels–Alder reaction makes two new rings. Draw the compound produced in each of these examples; try to predict stereochemistry (using models will help). In some cases, Lewis acid catalysts are used; that can be ignored for this problem.

(a)

(b)

Textbook Question

Predict the products of the following proposed Diels–Alder reactions.

(f)

Textbook Question

What stereochemical result would you expect if the Diels–Alder reaction with the free α,β- unsaturated ketone was faster than reaction with the iminium-bound alkene?

Textbook Question

(c)

Textbook Question

(d)

Textbook Question

What is the major product when the methoxy substituent in the preceding reaction is bonded to C-2 of the diene rather than to C-1?

Textbook Question

Explain why the following compounds are not optically active:

a. the product obtained from the reaction of 1,3-butadiene with cis-1,2-dichloroethene

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We predicted that the products would have a 1,2- or 1,4-relationship of the proper substituents. Draw the charge-separated resonance forms of the reactants to support these predictions.(a) (b)

Key Concepts

Resonance Structures

Charge Separation

Substituent Positioning

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We predicted that the products would have a 1,2- or 1,4-relationship of the proper substituents. Draw the charge-separated resonance forms of the reactants to support these predictions.
(a) (b)