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

Electron Withdrawing Groups

Organic Chemistry

19. Reactions of Aromatics: EAS and Beyond

Electron Withdrawing Groups

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Problem 52

Textbook Question

Despite the amino group being an ortho/para director, nitration of aniline gives the meta isomer predominantly. Explain this result.

Verified step by step guidance

Understand that the amino group (-NH2) is an ortho/para director due to its electron-donating nature, which typically increases electron density at the ortho and para positions of the benzene ring.

Recognize that nitration involves the introduction of a nitro group (-NO2) using a mixture of concentrated nitric acid (HNO3) and sulfuric acid (H2SO4), which generates the nitronium ion (NO2+), the active electrophile in the reaction.

Consider the reaction conditions: the strongly acidic environment protonates the amino group, converting it into an anilinium ion (-NH3+), which is a strong electron-withdrawing group.

Realize that the protonated amino group (-NH3+) is a meta director because it withdraws electron density from the ortho and para positions, making them less reactive towards electrophilic attack compared to the meta position.

Conclude that under these acidic conditions, the meta isomer is formed predominantly because the anilinium ion directs the incoming nitro group to the meta position, despite the original directing effects of the amino group.

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Key Concepts

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

Amino Group as an Ortho/Para Director

The amino group (-NH2) is an electron-donating group that stabilizes the positive charge on the aromatic ring during electrophilic aromatic substitution. This stabilization occurs primarily at the ortho and para positions relative to the amino group, making these positions more reactive towards electrophiles like nitronium ions (NO2+).

Electrophilic Aromatic Substitution Mechanism

Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. In the case of aniline nitration, the nitronium ion generated from nitric acid and sulfuric acid acts as the electrophile. The reaction proceeds through the formation of a sigma complex, which can lead to different isomers depending on the stability of the intermediates.

Steric Hindrance and Resonance Effects

While the amino group directs substitution to the ortho and para positions, steric hindrance can influence the outcome. In the case of aniline, the ortho position is hindered by the bulk of the amino group, making the meta position more favorable for substitution. Additionally, resonance effects can stabilize the meta product, leading to its predominance despite the ortho/para directing nature of the amino group.

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Related Practice

Textbook Question

For each horizontal row of substituted benzenes, indicate

c. the one that yields the highest percentage of meta product in an electrophilic aromatic substitution reaction.

Textbook Question

For each horizontal row of substituted benzenes, indicate

c. the one that yields the highest percentage of meta product in an electrophilic aromatic substitution reaction.

Textbook Question

Are the following substituents ortho–para directors or meta directors?

a. CH=CHC≡N

b. NO₂

c. CH₂OH

Open Question

Draw the resonance contributors for:

a. benzaldehyde

Textbook Question

Predict the major product(s) that would result when molecules (a)–(i) are allowed to react under the following conditions. (iv) chlorocyclopentane, AlCl₃, (v) 1-chloro-1-methylcyclohexane , AlCl₃, (vi) PhCOCl, AlCl₃. If no reaction will occur, indicate by writing NR.

(a)

Textbook Question

Predict the products of the following electrophilic aromatic substitution reactions.

(b)

Textbook Question

Predict the major product of the following electrophilic aromatic substitution reactions.

(c)

Textbook Question

Would you expect chlorination to occur ortho, para, or meta to the pyridinium ion in the following molecule? Explain your answer.

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