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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Problem 60

Textbook Question

While not covered explicitly in this chapter, the ene reaction occurs similarly to the Diels–Alder reaction but replaces the electrons from one bond in the diene with the electrons in a C―H bond. Draw the mechanism for the following reaction. [Number the carbons and draw in the hydrogens of the product. And, of course, make a note of bonds formed and bonds broken.]

Verified step by step guidance

Identify the components of the ene reaction: the 'ene' (alkene with an allylic hydrogen) and the 'enophile' (an electron-deficient species). In this case, determine which part of the molecule acts as the ene and which as the enophile.

Number the carbon atoms in the alkene and identify the allylic hydrogen that will participate in the reaction. This hydrogen is typically adjacent to the double bond.

Draw the initial step of the mechanism where the allylic hydrogen is transferred to the enophile. This involves the formation of a new C-H bond and the breaking of the original C-H bond.

Illustrate the movement of electrons: the π electrons from the alkene double bond will form a new σ bond with the enophile, while the electrons from the C-H bond will form a new π bond in the alkene.

Finally, draw the product of the reaction, ensuring that all new bonds are shown, and the numbering of carbons and hydrogens is clear. Highlight the bonds that were formed and those that were broken during the reaction.

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Key Concepts

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

Ene Reaction

The ene reaction is a type of pericyclic reaction where an alkene (ene) reacts with a compound containing a hydrogen atom (enophile) to form a new bond. It involves the transfer of electrons from a C-H bond to form a new C-C bond, similar to the Diels–Alder reaction but with different electron sources. Understanding the electron flow and bond formation is crucial for drawing the mechanism.

Pericyclic Reactions

Pericyclic reactions are a class of organic reactions that occur through a concerted process involving cyclic transition states. They are characterized by the redistribution of bonding electrons in a cyclic manner, often without intermediates. Familiarity with these reactions helps in understanding the mechanism of the ene reaction, as they share similar principles of electron movement and bond formation.

Mechanism Drawing

Drawing mechanisms involves illustrating the step-by-step process of a chemical reaction, showing how reactants transform into products. It requires identifying bonds broken and formed, numbering atoms for clarity, and indicating electron movement. This skill is essential for visualizing the ene reaction, ensuring accurate representation of the molecular changes and understanding the reaction pathway.

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Related Practice

Textbook Question

Predict the products of the following Diels–Alder reactions.

(c)

(d)

Textbook Question

The highly reactive triple bond of benzyne is a powerful dienophile. Predict the product of the Diels–Alder reaction of benzyne (from chlorobenzene and NaOH, heated) with cyclopentadiene.

Textbook Question

Provide a mechanism of the Diels–Alder reaction shown and predict the regioisomer that will form.

Textbook Question

Predict the product of the Diels–Alder reactions shown.

(a)

Textbook Question

Diene A participates in a fast and efficient Diels–Alder reaction with maleic anhydride, the powerful dienophile from Assessment 22.9. However, the related diene B does not undergo a Diels–Alder reaction. Why?

Textbook Question

Predict the product of the following Diels–Alder reactions. Where a racemic mixture is produced, show both enantiomers and explain how each is formed.

(d)

Textbook Question

Figure 22.16(a) <IMAGE> shows a unique example where the Diels–Alder reaction gives a single product (no enantiomers) regardless of whether the diene attacks the dienophile from the top or bottom.

(a) Show the product of the diene attacking from the bottom and confirm that the same product is obtained.

(b) What is special about this product that makes this true?

Textbook Question

Assuming the diene approaches the dienophile from the top, predict the product of the following Diels–Alder reactions.

(c)

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