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

EAS:Ortho vs. Para Positions

Organic Chemistry

19. Reactions of Aromatics: EAS and Beyond

EAS:Ortho vs. Para Positions

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6:30 minutes

Problem 5b

Textbook Question

(b) Explain why m-xylene undergoes nitration 100 times faster than p-xylene.

Verified step by step guidance

Understand the nitration reaction: Nitration is an electrophilic aromatic substitution reaction where a nitro group (-NO₂) is introduced into the aromatic ring. The rate of this reaction depends on the electron density of the aromatic ring and the positions of substituents.

Analyze the structure of m-xylene and p-xylene: Both compounds are derivatives of xylene (dimethylbenzene). In m-xylene, the two methyl groups are positioned meta to each other, while in p-xylene, the two methyl groups are positioned para to each other.

Consider the electron-donating effect of methyl groups: Methyl groups are electron-donating through both inductive (+I) and hyperconjugation effects. This increases the electron density on the aromatic ring, making it more reactive toward electrophiles like the nitronium ion (NO₂⁺).

Examine the steric hindrance in p-xylene: In p-xylene, the two methyl groups are positioned opposite each other, which can create steric hindrance at the para position. This steric hindrance can slow down the approach of the electrophile, reducing the rate of nitration compared to m-xylene.

Conclude the reasoning: In m-xylene, the methyl groups are positioned meta to each other, which minimizes steric hindrance and allows for a higher electron density at the reactive positions. This makes m-xylene undergo nitration much faster than p-xylene.

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Key Concepts

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

Electrophilic Aromatic Substitution

Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. The reaction is facilitated by the stability of the aromatic system, which allows for the formation of a resonance-stabilized carbocation intermediate. Understanding EAS is crucial for analyzing the reactivity of substituted aromatic compounds, such as m-xylene and p-xylene, in nitration reactions.

Substituent Effects

Substituent effects refer to how different groups attached to an aromatic ring influence its reactivity and orientation during electrophilic substitution. Electron-donating groups, like methyl groups in xylene, increase the electron density of the ring, enhancing its reactivity towards electrophiles. The position of these substituents (ortho, meta, para) also affects the rate of reaction, with m-xylene being more reactive than p-xylene due to the favorable resonance stabilization of the intermediate formed during nitration.

Resonance Stabilization

Resonance stabilization is a key concept in organic chemistry that describes how the electron density in a molecule can be delocalized over multiple atoms, leading to increased stability. In the case of m-xylene, the formation of a resonance-stabilized carbocation during nitration is more favorable compared to p-xylene. This increased stabilization in m-xylene's transition state results in a significantly faster reaction rate, making it more reactive towards nitration.

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