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

19. Reactions of Aromatics: EAS and Beyond

Nucleophilic Aromatic Substitution

Organic Chemistry

19. Reactions of Aromatics: EAS and Beyond

Nucleophilic Aromatic Substitution

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6:16 minutes

Problem 12a

Textbook Question

Propose a mechanism for the following reaction:

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Step 1: Analyze the reactant and product. The reactant is pyridine, a six-membered aromatic ring containing one nitrogen atom. The product is 2-pyridone, which has a ketone group at the 2-position and an NH group replacing the nitrogen atom in the aromatic ring. This indicates a tautomerization reaction involving the addition of water and rearrangement of bonds.

Step 2: Recognize the role of KOH and water. KOH acts as a base, and water provides the necessary environment for the reaction. The heat (Δ) facilitates the reaction by providing energy for bond rearrangement.

Step 3: Initiate the mechanism by protonation of pyridine. The nitrogen atom in pyridine is nucleophilic and can interact with water to form a protonated intermediate. This step disrupts the aromaticity of pyridine.

Step 4: Deprotonation and nucleophilic attack. The hydroxide ion (OH⁻) from KOH can attack the 2-position of the pyridine ring, leading to the formation of an intermediate where the aromaticity is temporarily lost.

Step 5: Rearrange bonds to restore aromaticity and form the ketone group. The intermediate undergoes tautomerization, where a hydrogen atom shifts and the double bonds rearrange to form the final product, 2-pyridone, with the ketone group at the 2-position and the NH group in the ring.

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Key Concepts

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

Nucleophilic Aromatic Substitution (NAS)

Nucleophilic Aromatic Substitution is a reaction mechanism where a nucleophile replaces a leaving group on an aromatic ring. This process typically occurs when the aromatic compound has electron-withdrawing groups that stabilize the negative charge developed during the reaction. Understanding this mechanism is crucial for predicting the outcome of reactions involving aromatic compounds, especially when proposing reaction pathways.

Mechanism Steps

The mechanism of nucleophilic aromatic substitution generally involves two main steps: the formation of a Meisenheimer complex, where the nucleophile attacks the aromatic ring, and the subsequent elimination of the leaving group. This two-step process is essential for understanding how the nucleophile interacts with the aromatic system and how the reaction proceeds to completion.

Role of Base and Solvent

In the reaction shown, KOH acts as a base and water as a solvent, which are critical for facilitating the nucleophilic attack. The base can deprotonate the nucleophile, enhancing its nucleophilicity, while the solvent can stabilize the transition state. Recognizing the roles of the base and solvent helps in understanding the reaction conditions that favor nucleophilic aromatic substitution.

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Related Practice

Textbook Question

Show how the substituents containing the azo group (N=N) can facilitate both electrophilic and nucleophilic aromatic substitution.

(a)

Textbook Question

We have considered nucleophilic aromatic substitution of pyridine at the 2-position and 3-position but not at the 4-position. Complete the three possible cases by showing the mechanism for the reaction of methoxide ion with 4-chloropyridine. Show how the intermediate is stabilized by delocalization of the charge onto the nitrogen atom.

Textbook Question

How do the mechanisms of the following reactions differ?

Textbook Question

What are the products of the following reactions?

Textbook Question

Predict the products of the following nucleophilic aromatic substitution reactions.

(c)

Textbook Question

Suggest an arrow-pushing mechanism of the following rearrangement.

Textbook Question

Predict the product of the following substitution/addition reactions involving phenoxides. [Because this problem represents a review of current and previous material, section numbers have been provided for your reference.]

(d)

Textbook Question

What are the products of the following reactions?

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