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

Benzyne

Organic Chemistry

19. Reactions of Aromatics: EAS and Beyond

Benzyne

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3:54 minutes

Problem 33b

Textbook Question

b. At what position does pyridine-N-oxide undergo electrophilic aromatic substitution?

Verified step by step guidance

Pyridine-N-oxide is a derivative of pyridine where an oxygen atom is bonded to the nitrogen atom, creating a positively charged nitrogen and a negatively charged oxygen. This alters the electronic distribution in the ring, making it different from regular pyridine.

In electrophilic aromatic substitution (EAS), the position of substitution is determined by the electronic effects of substituents. The oxygen in pyridine-N-oxide withdraws electron density from the nitrogen atom, which in turn affects the electron density at the various positions of the aromatic ring.

The resonance structures of pyridine-N-oxide show that the electron density is reduced at the ortho (positions 2 and 6) and para (position 4) positions relative to the nitrogen atom. However, the meta positions (positions 3 and 5) retain relatively higher electron density.

Since electrophiles are attracted to regions of higher electron density, the electrophilic aromatic substitution reaction will preferentially occur at the meta positions (positions 3 and 5) of pyridine-N-oxide.

To summarize, pyridine-N-oxide undergoes electrophilic aromatic substitution at the meta positions (positions 3 and 5) due to the electronic effects of the N-oxide group, which directs substitution to these positions.

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Key Concepts

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

Electrophilic Aromatic Substitution (EAS)

Electrophilic Aromatic Substitution is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. This process typically involves the formation of a sigma complex, where the aromaticity is temporarily lost, followed by deprotonation to restore aromaticity. Understanding EAS is crucial for predicting the reactivity of aromatic compounds, including heterocycles like pyridine.

Pyridine and its Derivatives

Pyridine is a six-membered aromatic ring containing one nitrogen atom, which influences its reactivity compared to benzene. The nitrogen atom in pyridine is electron-withdrawing due to its electronegativity, which affects the positions where electrophilic substitution can occur. Recognizing the role of nitrogen in pyridine derivatives is essential for determining the regioselectivity of EAS reactions.

Regioselectivity in Electrophilic Aromatic Substitution

Regioselectivity refers to the preference of an electrophile to attack specific positions on an aromatic ring during substitution reactions. In the case of pyridine-N-oxide, the presence of the nitrogen atom and the oxygen atom influences the electron density on the ring, making certain positions more favorable for electrophilic attack. Understanding regioselectivity helps predict the outcome of reactions involving substituted aromatic compounds.

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