| Aromatic Hydrocarbons – Important Questions, Reactions & Mechanisms [NEET Focused] |
Aromatic hydrocarbons are one of the most important classes of organic compounds, especially in the NEET Chemistry syllabus. These compounds contain a benzene ring or related ring systems and show special stability due to delocalized π-electrons. In this article, we will cover the essential reactions, properties, and NEET-level questions on aromatic hydrocarbons to help you score well.
📌 What Are Aromatic Hydrocarbons?
- Also called arenes, these compounds have one or more benzene rings.
- Common examples include benzene, toluene, aniline, and phenol.
- They follow Huckel's Rule (4n+2 π-electrons).
🔬 General Properties of Aromatic Hydrocarbons
- Planar structure with delocalized electrons.
- High chemical stability (resonance energy).
- Undergo electrophilic substitution reactions.
- Burn with a sooty flame due to high carbon content.
⚗️ Important Reactions of Aromatic Hydrocarbons
| Reaction | Type | Example |
|---|---|---|
| Halogenation | Electrophilic substitution | C6H6 + Cl2 → C6H5Cl + HCl |
| Nitration | Electrophilic substitution | Benzene + HNO3/H2SO4 → Nitrobenzene |
| Friedel–Crafts Alkylation | Electrophilic substitution | C6H6 + CH3Cl → C6H5CH3 |
| Oxidation | Side chain oxidation | Toluene → Benzoic acid |
🧪 Mechanism Example – Nitration of Benzene
- Formation of nitronium ion: HNO3 + H2SO4 → NO2+ + H2O
- Attack of electrophile on benzene ring.
- Restoration of aromaticity by loss of H+.
📝 NEET Level Important Questions (With Answers)
Q1. Which compound is an aromatic hydrocarbon?
A. Cyclohexane
B. Benzene
C. Ethylene
D. Acetylene
Answer: B. Benzene
Explanation: Benzene has a delocalized π-system and satisfies Huckel's rule.
Q2. Which reaction is used for the preparation of toluene?
A. Nitration
B. Halogenation
C. Friedel–Crafts Alkylation
D. Oxidation
Answer: C. Friedel–Crafts Alkylation
Q3. The IUPAC name of benzene with a –CH3 group is:
A. Benzyl
B. Toluene
C. Methylbenzene
D. Phenylmethane
Answer: C. Methylbenzene
Q4. What is the product of benzene + Br2/FeBr3?
A. Bromobenzene
B. Benzyl bromide
C. Nitrobenzene
D. Phenol
Answer: A. Bromobenzene
Q5. Aromaticity is defined by:
A. Resonance
B. Planarity
C. Huckel’s rule
D. All of the above
Answer: D. All of the above
📚 Summary
Aromatic hydrocarbons are crucial in organic chemistry, especially for NEET and board exams. Understanding their structure, reactions, and mechanisms helps in mastering many important concepts. Keep practicing with MCQs and focus on electrophilic substitution reactions in depth.
🧠 Pro Tips for NEET
- Revise mechanisms like nitration, sulfonation, and Friedel–Crafts.
- Use flashcards for functional groups.
- Practice previous year questions regularly.
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