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

Electrophilic Aromatic Substitution

Organic Chemistry

19. Reactions of Aromatics: EAS and Beyond

Electrophilic Aromatic Substitution

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Problem 15

Textbook Question

Rank imidazole, pyrrole, and benzene from most reactive to least reactive toward electrophilic aromatic substitution.

Verified step by step guidance

Understand the concept of electrophilic aromatic substitution (EAS): This reaction involves the replacement of a hydrogen atom on an aromatic ring with an electrophile. The reactivity of the aromatic compound depends on the electron density of the ring, which is influenced by the substituents or heteroatoms present in the structure.

Analyze the structure of imidazole: Imidazole contains two nitrogen atoms in a five-membered aromatic ring. One nitrogen has a lone pair that participates in the aromaticity of the ring, while the other nitrogen has a lone pair that is not involved in aromaticity. This makes imidazole electron-rich and highly reactive toward electrophiles.

Analyze the structure of pyrrole: Pyrrole is a five-membered aromatic ring with one nitrogen atom. The lone pair on the nitrogen is delocalized into the aromatic system, increasing the electron density of the ring. However, it is slightly less electron-rich compared to imidazole because it has only one nitrogen contributing to the electron density.

Analyze the structure of benzene: Benzene is a six-membered aromatic ring with no heteroatoms. Its electron density is evenly distributed across the ring, making it less reactive toward electrophiles compared to imidazole and pyrrole.

Rank the compounds based on their reactivity: Since imidazole has the highest electron density due to the presence of two nitrogen atoms, it is the most reactive. Pyrrole, with one nitrogen atom, is less reactive than imidazole but more reactive than benzene. Benzene, with no heteroatoms, is the least reactive. Therefore, the order of reactivity is: imidazole > pyrrole > benzene.

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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. The reactivity of the aromatic compound is influenced by the electron density of the ring, which is affected by substituents. Understanding EAS is crucial for ranking the reactivity of compounds like imidazole, pyrrole, and benzene.

Aromaticity and Electron Density

Aromatic compounds are characterized by their stable ring structure and delocalized π-electrons, which contribute to their unique reactivity. The electron density on the ring determines how readily it can react with electrophiles. Compounds with higher electron density are generally more reactive in EAS, making the concept of aromaticity essential for comparing imidazole, pyrrole, and benzene.

Substituent Effects

The presence of different substituents on an aromatic ring can significantly influence its reactivity toward electrophiles. Electron-donating groups increase electron density and enhance reactivity, while electron-withdrawing groups decrease it. In the case of imidazole, pyrrole, and benzene, understanding how their structures affect electron donation is key to ranking their reactivity in EAS.

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Related Practice

Textbook Question

What is the major product of the following reactions?

Textbook Question

What is the major product of the following reactions?

Textbook Question

Show how the following compounds can be prepared from the given starting material.

Textbook Question

When pyrrole is added to a dilute solution of D₂SO₄ in D₂O, 2-deuteriopyrrole is formed. Propose a mechanism to account for the formation of this compound.

Textbook Question

If Kekulé's original hypothesis had been correct and benzene was really an equilibrium between two structures, how many distinct isomers would exist for 1,2-dichlorobenzene?

Textbook Question

Electrophilic aromatic substitution usually occurs at the 1-position of naphthalene, also called the a position. Predict the major products of the reactions of naphthalene with the following reagents.

(a) HNO₃, H₂SO₄

(b) Br₂, FeBr₃

Textbook Question

Biphenyl is two benzene rings joined by a single bond. The site of substitution for a biphenyl is determined by (1) which phenyl ring is more activated (or less deactivated), and (2) which position on that ring is most reactive, using the fact that a phenyl substituent is activating and ortho, para-directing.

a. Use resonance forms of a sigma complex to show why a phenyl substituent should be ortho, para-directing.

(vi)

Textbook Question

Unlike most other electrophilic aromatic substitutions, sulfonation is often reversible (see Section 17-4). When one sample of toluene is sulfonated at 0 °C and another sample is sulfonated at 100 °C, the following ratios of substitution products result:

a. Explain the change in the product ratios when the temperature is increased.

b. Predict what will happen when the product mixture from the reaction at 0 °C is heated to 100 °C.

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