Nitration of benzene MCQs With Answer

Nitration of benzene MCQs With Answer is an essential topic for B. Pharm students studying aromatic chemistry and synthesis. This concise introduction covers the nitration of benzene, the generation of the nitronium ion (NO2+), mixed-acid reagents (concentrated nitric and sulfuric acids), electrophilic aromatic substitution mechanism, regiochemistry, and practical aspects like temperature control, safety and downstream reduction to amines. Understanding nitration is crucial for designing nitro-containing drug intermediates and predicting directing effects in substituted benzenes. These MCQs focus on mechanism, reagents, kinetics, product distribution and pharmaceutical relevance to build exam-ready knowledge. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which reagent mixture is classically used for the nitration of benzene?

• Concentrated nitric acid alone
• Concentrated nitric acid and concentrated sulfuric acid (mixed acid)
• Hydrochloric acid and nitric acid
• AlCl3 and nitric acid

Correct Answer: Concentrated nitric acid and concentrated sulfuric acid (mixed acid)

Q2. What is the active electrophile in the nitration of benzene?

• Nitrate ion (NO3−)
• Nitronium ion (NO2+)
• Nitric oxide (NO)
• Nitrogen dioxide (NO2)

Correct Answer: Nitronium ion (NO2+)

Q3. What is the primary role of sulfuric acid in the mixed acid nitration?

• Acts as a nucleophile to attack benzene
• Protonates nitric acid to generate the nitronium ion
• Oxidizes benzene to phenol
• Serves only as a solvent with no chemical role

Correct Answer: Protonates nitric acid to generate the nitronium ion

Q4. The nitration of benzene proceeds through which general mechanism?

• Nucleophilic aromatic substitution
• Electrophilic aromatic substitution
• Radical substitution
• Pericyclic addition

Correct Answer: Electrophilic aromatic substitution

Q5. The key intermediate formed during electrophilic nitration of benzene is called:

• Carbocation without resonance
• Arenium (σ-complex) ion
• Benzyl radical
• Quinone methide

Correct Answer: Arenium (σ-complex) ion

Q6. What is the major organic product when benzene is nitrated under standard mixed-acid conditions?

• Aniline
• Nitrobenzene
• Phenol
• Benzaldehyde

Correct Answer: Nitrobenzene

Q7. Which substituent directs incoming electrophiles to the meta position during nitration?

• –OH (hydroxyl)
• –NH2 (amino)
• –NO2 (nitro)
• –CH3 (methyl)

Correct Answer: –NO2 (nitro)

Q8. Which substituent strongly activates the benzene ring toward nitration?

• –NO2 (nitro)
• –SO3H (sulfonic acid)
• –OCH3 (methoxy)
• –COOH (carboxylic acid)

Correct Answer: –OCH3 (methoxy)

Q9. Nitration is typically exothermic. What is the primary reason for controlling temperature during nitration?

• To increase the formation of H2O
• To avoid over-nitration and side reactions
• To deactivate sulfuric acid
• To generate more nitric oxide

Correct Answer: To avoid over-nitration and side reactions

Q10. What is a common laboratory hazard associated with the nitration reaction?

• Formation of explosive nitro compounds if uncontrolled
• Generation of hydrogen gas causing fire
• Production of inert nitrogen gas lowering yield
• Formation of peroxides that are harmless

Correct Answer: Formation of explosive nitro compounds if uncontrolled

Q11. In nitration, which species does sulfuric acid form after protonating nitric acid?

• Nitronium sulfate
• Bisulfate ion (HSO4−)
• Nitrate radical
• Nitric oxide gas

Correct Answer: Bisulfate ion (HSO4−)

Q12. Which reagent combination will reduce nitrobenzene to aniline in a lab setting?

• Sn/HCl or Fe/HCl
• PCC (pyridinium chlorochromate)
• KMnO4 in basic solution
• Br2/FeBr3

Correct Answer: Sn/HCl or Fe/HCl

Q13. Which position is favored upon nitration of toluene under standard conditions?

• Only meta
• Ortho and para (with para often favored)
• Only para
• Only ortho

Correct Answer: Ortho and para (with para often favored)

Q14. Why is nitration of nitrobenzene much slower than benzene itself?

• Nitro group strongly activates the ring
• Nitro group strongly deactivates the ring by electron withdrawal
• Nitrobenzene is insoluble in mixed acid
• Nitrobenzene forms radicals too readily

Correct Answer: Nitro group strongly deactivates the ring by electron withdrawal

Q15. Which description best explains why electron-donating groups increase nitration rate?

• They destabilize the arenium ion
• They decrease aromaticity permanently
• They stabilize the electrophilic σ-complex intermediate
• They convert NO2+ to NO3−

Correct Answer: They stabilize the electrophilic σ-complex intermediate

Q16. What is the effect of adding excess sulfuric acid in a nitration mixture?

• Decreases formation of nitronium ion
• Promotes dehydration of nitric acid to form more NO2+
• Neutralizes nitric acid making reaction slower
• Converts nitrobenzene to benzene

Correct Answer: Promotes dehydration of nitric acid to form more NO2+

Q17. Which solvent system is typically used in industrial nitration of benzene?

• Water only
• Mixed concentrated nitric and sulfuric acids
• Pure methanol
• Hexane solution

Correct Answer: Mixed concentrated nitric and sulfuric acids

Q18. In the nitration mechanism, what is the rate-determining step?

• Formation of nitronium ion from nitric acid
• Nucleophilic attack of benzene on NO2+
• Deprotonation of the σ-complex to restore aromaticity
• Formation of nitric oxide gas

Correct Answer: Nucleophilic attack of benzene on NO2+

Q19. Which product ratio is typically expected when nitrating anisole (methoxybenzene)?

• Mostly meta product
• Predominantly ortho and para, with para often major
• Only monosubstituted ortho
• No reaction occurs

Correct Answer: Predominantly ortho and para, with para often major

Q20. Which condition favors mononitration over dinitration?

• High temperature and excess nitric acid
• Low temperature and controlled addition of nitric acid
• Using radical initiators
• Adding metal catalysts like AlCl3

Correct Answer: Low temperature and controlled addition of nitric acid

Q21. Which analytical spectroscopy is most useful to confirm formation of nitrobenzene?

• Proton NMR showing a strong NH signal
• IR spectroscopy showing strong NO2 stretches around 1500–1350 cm−1
• UV-Vis showing no absorption
• Optical rotation measurement

Correct Answer: IR spectroscopy showing strong NO2 stretches around 1500–1350 cm−1

Q22. Which statement about nitration of activated aromatic rings is true?

• Activated rings never undergo nitration
• Activated rings nitration is faster and may give poly-nitration if uncontrolled
• Activated rings only give meta products
• Activation by -NO2 speeds nitration

Correct Answer: Activated rings nitration is faster and may give poly-nitration if uncontrolled

Q23. Which reagent would you avoid when nitrating an aromatic amine (aniline) directly?

• Acetyl chloride to protect the amine
• Mixed acid (concentrated HNO3/H2SO4) without protection
• Acetic anhydride for acetylation
• Sodium nitrite for diazotization (separate reaction)

Correct Answer: Mixed acid (concentrated HNO3/H2SO4) without protection

Q24. What is the effect of electron-withdrawing groups on the position and rate of nitration?

• They increase rate and direct ortho/para
• They decrease rate and direct meta
• They have no effect
• They always cause oxidation instead

Correct Answer: They decrease rate and direct meta

Q25. Which is the correct order of reactivity toward nitration for these substituents: –NH2, –CH3, –NO2?

• –NO2 > –CH3 > –NH2
• –NH2 > –CH3 > –NO2
• –CH3 > –NH2 > –NO2
• All equal

Correct Answer: –NH2 > –CH3 > –NO2

Q26. Why are protecting groups used before nitrating aromatic amines in pharmaceutical synthesis?

• To make the amine more nucleophilic for nitration
• To prevent oxidation or protonation of the amine and undesired side reactions
• To remove the amine completely
• Protecting groups are not used

Correct Answer: To prevent oxidation or protonation of the amine and undesired side reactions

Q27. Which of the following best describes the electronic effect of a nitro group on a benzene ring?

• Strong electron-donating by resonance
• Strong electron-withdrawing by both resonance and induction
• No electronic effect
• Only inductive donation

Correct Answer: Strong electron-withdrawing by both resonance and induction

Q28. In pharmaceutical synthesis, why might one prefer nitration to introduce an amino group indirectly?

• Nitration directly gives amino compounds without reduction
• Nitro group can be placed selectively and then reduced to an amine later
• Nitration is the only way to add an amino group
• Nitro is more reactive than amine in drug action

Correct Answer: Nitro group can be placed selectively and then reduced to an amine later

Q29. Which aromatic substrate will give mainly meta-nitro product upon nitration?

• Toluene
• Phenol
• Benzoic acid
• Anisole

Correct Answer: Benzoic acid

Q30. What happens to aromaticity when the σ-complex (arenium ion) forms during nitration?

• Aromaticity is fully retained without change
• Aromaticity is temporarily lost and regained after deprotonation
• It becomes antiaromatic permanently
• Aromaticity increases permanently

Correct Answer: Aromaticity is temporarily lost and regained after deprotonation

Q31. Which reagent is typically used to quench a nitration reaction safely?

• Cold water or ice to dilute and cool the reaction mixture
• Pure benzene to neutralize acids
• Concentrated sulfuric acid to stop reaction
• Sodium metal to react with acids

Correct Answer: Cold water or ice to dilute and cool the reaction mixture

Q32. Which of the following substituents will most strongly direct nitration to the ortho/para positions?

• –NO2
• –CHO
• –OCH3
• –COOH

Correct Answer: –OCH3

Q33. Which kinetic descriptor increases when benzene is substituted with an electron-donating group?

• Activation energy for nitration increases
• Rate of nitration decreases
• Rate of nitration increases
• Reaction becomes endothermic

Correct Answer: Rate of nitration increases

Q34. For nitration in industry, why is continuous addition of nitric acid often used?

• To maintain low reagent concentration and control heat, reducing side products
• To ensure rapid formation of dinitro compounds
• To avoid formation of nitronium ion
• To convert sulfuric acid to sulfur dioxide

Correct Answer: To maintain low reagent concentration and control heat, reducing side products

Q35. Which observation in IR spectroscopy indicates a nitro group in an aromatic compound?

• Strong peaks near 1700 cm−1 only
• Strong symmetric and asymmetric NO2 stretches near 1500 and 1350 cm−1
• Sharp OH peak at 3200–3600 cm−1 only
• Triple bond stretch at 2200 cm−1

Correct Answer: Strong symmetric and asymmetric NO2 stretches near 1500 and 1350 cm−1

Q36. What would be the major nitration product of chlorobenzene?

• Only para-nitrochlorobenzene
• Mixture of ortho and para nitrochlorobenzene with ortho and para favored over meta
• Only meta-nitrochlorobenzene
• No reaction due to chlorine

Correct Answer: Mixture of ortho and para nitrochlorobenzene with ortho and para favored over meta

Q37. In electrophilic aromatic substitution, which is true about resonance stabilization?

• Resonance destabilizes σ-complex
• Resonance stabilization of intermediate determines regioselectivity
• Resonance is irrelevant for nitration
• Only inductive effects matter

Correct Answer: Resonance stabilization of intermediate determines regioselectivity

Q38. What safety precaution is essential when performing nitration reactions at lab scale?

• Perform reaction at high temperature to speed it up
• Use proper cooling, slow addition of nitric acid and explosion precautions
• No ventilation is required
• Mix acids with base first

Correct Answer: Use proper cooling, slow addition of nitric acid and explosion precautions

Q39. Which is a common downstream transformation of nitrobenzene in drug synthesis?

• Oxidation to benzoic acid
• Reduction to aniline derivatives
• Conversion to alkyl halides directly
• Formation of Grignard reagent

Correct Answer: Reduction to aniline derivatives

Q40. Which factor does NOT significantly affect regioselectivity in nitration of substituted benzenes?

• Electronic effects (resonance/induction) of substituents
• Steric hindrance from existing substituents
• Reaction temperature and solvent effects
• Color of the reaction flask

Correct Answer: Color of the reaction flask

Q41. Which species directly attacks the aromatic ring in the rate-determining step?

• Bisulfate ion (HSO4−)
• Nitronium ion (NO2+)
• Nitrate ion (NO3−)
• Water molecule

Correct Answer: Nitronium ion (NO2+)

Q42. What product distribution is expected from nitration of m-xylene?

• Mostly meta substitution only
• Mixture with nitration at positions activated by methyl groups, giving mainly 2- and 4-positions relative to one methyl
• Only para to both methyls
• No reaction

Correct Answer: Mixture with nitration at positions activated by methyl groups, giving mainly 2- and 4-positions relative to one methyl

Q43. Which experimental technique helps separate nitrobenzene from reaction mixture?

• Simple distillation using difference in boiling points
• Centrifugation only
• Recrystallization from water (nitrobenzene is liquid)
• Filtering solids directly

Correct Answer: Simple distillation using difference in boiling points

Q44. Why is nitration less favorable in strongly deactivated rings like trinitrobenzene?

• Electron density is too low to form the σ-complex effectively
• They are too soluble in acids
• They form radicals instead
• They spontaneously combust

Correct Answer: Electron density is too low to form the σ-complex effectively

Q45. Which of the following is a correct description of nitration selectivity in presence of multiple substituents?

• The strongest activating group usually dominates regiochemistry
• All substituents have equal influence always
• Only steric effects determine product
• Regiochemistry cannot be predicted

Correct Answer: The strongest activating group usually dominates regiochemistry

Q46. In the context of green chemistry, what is a concern regarding classical nitration methods?

• They produce no waste
• Use of large amounts of concentrated acids and generation of acidic waste
• Nitration is always atom-economical and benign
• They eliminate need for catalysts

Correct Answer: Use of large amounts of concentrated acids and generation of acidic waste

Q47. Which substituent combination on benzene will most likely give para-nitro product as the major isomer?

• –CF3 substituent only
• –CH3 substituent (toluene)
• –NO2 substituent only
• –COOH substituent only

Correct Answer: –CH3 substituent (toluene)

Q48. What is the expected directing effect of a sulfonic acid group (–SO3H) during nitration?

• Strong ortho/para director and activator
• Meta director and deactivator
• No directing effect
• Converts ring to alkyl halide

Correct Answer: Meta director and deactivator

Q49. Which laboratory observation suggests formation of nitronium ion in the nitration mixture?

• Evolution of nitrogen gas rapidly
• Appearance of a yellow to red color due to NO2+/charge-transfer species
• Precipitation of solid benzene
• Strong basic odor

Correct Answer: Appearance of a yellow to red color due to NO2+/charge-transfer species

Q50. In designing a pharmaceutical synthesis route, why might controlled regioselective nitration be preferred over direct amination?

• Direct amination is always cheaper and cleaner
• Nitration allows introduction of a protected functional handle (nitro) that can be selectively reduced to an amine later
• Nitration always gives a single product with no need for purification
• Aromatic amines cannot be made from nitro groups

Correct Answer: Nitration allows introduction of a protected functional handle (nitro) that can be selectively reduced to an amine later

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