Friedel–Crafts reactions and directive influence of substituents - Question Bank

1. The directive influence of the alkyl group (-R) in electrophilic aromatic substitution is:
A) Meta-directing and deactivating
B) Ortho, para-directing and deactivating
C) Meta-directing and activating
D) Ortho, para-directing and activating
2. Which of the following is a characteristic feature of Friedel-Crafts acylation that makes it superior to alkylation for controlled synthesis?
A) The acyl group is activating, allowing further acylation.
B) The acyl group is deactivating, preventing polyacylation.
C) The acyl group is easily removed by reduction.
D) The reaction is stereospecific.
3. When benzene is reacted with carbon tetrachloride (CCl₄) in the presence of AlCl₃, the product is:
A) Chlorobenzene
B) Benzotrichloride
C) Diphenylmethane
D) No reaction
4. The deactivating effect of the cyano group (-CN) in electrophilic aromatic substitution is due to:
A) Inductive effect only
B) Resonance effect only
C) Both inductive and resonance effects, with inductive effect being dominant
D) Both inductive and resonance effects, with resonance effect being dominant
5. Which of the following carbocations is most stable and likely to form in a Friedel-Crafts alkylation if possible?
A) Methyl carbocation
B) Ethyl carbocation
C) Isopropyl carbocation
D) Tertiary butyl carbocation
6. In the Friedel-Crafts reaction, the aromatic ring acts as a:
A) Nucleophile
B) Electrophile
C) Radical
D) Base
7. Which of the following substituents is a weak deactivator and an ortho, para-director?
A) -NO₂
B) -SO₃H
C) -Cl
D) -CHO
8. What is the reason behind the ortho, para-directing nature of the methoxy group (-OCH₃)?
A) Strong inductive electron withdrawal
B) Strong inductive electron donation
C) Resonance electron donation
D) Steric hindrance at ortho positions
9. The use of excess Lewis acid in Friedel-Crafts alkylation is sometimes necessary because:
A) The alkyl halide is a poor electrophile.
B) The product is more reactive than the reactant.
C) The catalyst gets complexed with the product.
D) The reaction is highly reversible.
10. Which of the following reactions is an example of Friedel-Crafts acylation?
A) Benzene + CH₃Cl + AlCl₃ → Toluene
B) Benzene + CH₃COCl + AlCl₃ → Acetophenone
C) Toluene + HNO₃ + H₂SO₄ → Nitrotoluenes
D) Phenol + Br₂ → Bromophenols
11. The Friedel-Crafts reaction is generally not applicable to aromatic compounds containing which type of substituents?
A) Electron-donating groups
B) Electron-withdrawing groups
C) Halogens
D) Alkyl groups
12. In electrophilic substitution of nitrobenzene, the incoming electrophile is directed to the meta position because the nitro group:
A) Activates the ortho and para positions
B) Deactivates the meta position
C) Deactivates the ortho and para positions more than the meta position
D) Activates the meta position
13. Which of the following is a strong activating group and an ortho, para-director?
A) -NO₂
B) -CN
C) -OH
D) -SO₃H
14. The directive influence of a substituent can be explained by considering resonance and inductive effects on the stability of the:
A) Carbanion intermediate
B) Free radical intermediate
C) Sigma complex (arenium ion) intermediate
D) Transition state only
15. What product is formed when benzene is treated with acetyl chloride and AlCl₃, followed by hydrolysis?
A) Ethylbenzene
B) Acetophenone
C) Benzene
D) Toluene
16. Why is aniline not suitable for Friedel-Crafts reactions?
A) The amino group is a strong deactivator.
B) The amino group reacts with the Lewis acid catalyst, deactivating it.
C) The amino group undergoes oxidation under the reaction conditions.
D) The amino group is a weak ortho, para-director.
17. The reaction of benzene with an alkyl halide in the presence of a Lewis acid catalyst is known as:
A) Friedel-Crafts acylation
B) Friedel-Crafts alkylation
C) Williamson ether synthesis
D) Electrophilic addition
18. Which of the following is NOT a typical Lewis acid catalyst for Friedel-Crafts reactions?
A) AlCl₃
B) FeCl₃
C) BF₃
D) H₂O
19. In the Friedel-Crafts alkylation of benzene with methyl chloride, the electrophile is:
A) CH₃⁺
B) CH₃Cl
C) AlCl₄⁻
D) HCl
20. The directive influence of a substituent on electrophilic aromatic substitution is primarily determined by:
A) Its size and steric hindrance
B) Its ability to donate or withdraw electron density from the ring
C) The type of catalyst used
D) The temperature of the reaction
21. Which group directs incoming electrophiles predominantly to the meta position and deactivates the ring?
A) -NH₂
B) -OH
C) -COOH
D) -OCH₃
22. The reaction of benzene with fuming sulfuric acid (H₂SO₄ + SO₃) leads to:
A) Benzaldehyde
B) Benzenesulfonic acid
C) Nitrobenzene
D) Phenyl sulfate
23. In the sulfonation of benzene, what is the electrophile?
A) SO₂
B) SO₃
C) HSO₄⁻
D) H₂SO₄
24. Consider the nitration of chlorobenzene. The major products are ortho and para isomers. This indicates that the chlorine atom is:
A) Meta-directing and activating
B) Ortho, para-directing and activating
C) Meta-directing and deactivating
D) Ortho, para-directing and deactivating
25. Which reaction involves the formation of a sigma complex as an intermediate?
A) Nucleophilic addition
B) Electrophilic aromatic substitution
C) Free radical polymerization
D) Elimination reaction
26. What is the primary reason for the rearrangement of carbocations in Friedel-Crafts alkylation?
A) To form a less stable carbocation
B) To form a more stable carbocation (e.g., secondary to tertiary)
C) To increase the electronegativity of the carbon atom
D) To facilitate nucleophilic attack
27. The carbocation formed in the Friedel-Crafts alkylation of benzene with n-propyl chloride is:
A) Primary carbocation
B) Secondary carbocation
C) Tertiary carbocation
D) Resonance-stabilized carbocation
28. Which of the following reagents would be used for the Friedel-Crafts acylation of benzene to form benzophenone?
A) Benzoyl chloride and AlCl₃
B) Benzyl chloride and AlCl₃
C) Benzene and acetyl chloride
D) Benzene and phosgene
29. Friedel-Crafts acylation is an example of which type of reaction mechanism?
A) Nucleophilic addition-elimination
B) Electrophilic addition-elimination
C) Free radical substitution
D) Nucleophilic substitution
30. When anisole (methoxybenzene) is subjected to nitration, the major product is:
A) o-Nitroanisole
B) m-Nitroanisole
C) p-Nitroanisole
D) A mixture of o- and p-nitroanisole
31. The relative rates of electrophilic substitution of monosubstituted benzenes follow the order:
A) Activating > Halogens > Deactivating
B) Halogens > Activating > Deactivating
C) Deactivating > Activating > Halogens
D) Activating > Deactivating > Halogens
32. Which of the following substituents is least activating for electrophilic aromatic substitution?
A) -OH
B) -NH₂
C) -OCH₃
D) -F
33. In the electrophilic substitution of phenol, which positions are most reactive?
A) Meta positions
B) Ortho and para positions
C) Ortho positions only
D) Para positions only
34. Halogens (like Cl, Br) are ortho, para-directors but are deactivating. Why?
A) They withdraw electron density inductively but donate electron density via resonance.
B) They donate electron density inductively but withdraw electron density via resonance.
C) They are strong electron donors both inductively and via resonance.
D) They are strong electron withdrawers both inductively and via resonance.
35. When toluene undergoes nitration, the major product formed is:
A) o-Nitrotoluene
B) m-Nitrotoluene
C) p-Nitrotoluene
D) A mixture of all three isomers in equal proportions
36. The nitro group (-NO₂) is a strong deactivator and a:
A) Ortho, para-director
B) Meta-director
C) Ortho-director
D) Para-director
37. Which of the following is an example of a meta-directing group in electrophilic aromatic substitution?
A) -NH₂
B) -CH₃
C) -Cl
D) -CHO
38. What is the directive influence of an electron-withdrawing group (EWG) in electrophilic aromatic substitution?
A) Ortho, para-directing and activating
B) Meta-directing and activating
C) Ortho, para-directing and deactivating
D) Meta-directing and deactivating
39. Which of the following is an example of an ortho, para-directing group in electrophilic aromatic substitution?
A) -NO₂
B) -SO₃H
C) -OH
D) -CN
40. When a monosubstituted benzene is subjected to electrophilic aromatic substitution, the incoming electrophile usually attacks at positions directed by the substituent. What is the directive influence of an electron-donating group (EDG)?
A) Ortho, para-directing and activating
B) Meta-directing and activating
C) Ortho, para-directing and deactivating
D) Meta-directing and deactivating
41. What is the correct order of reactivity of halobenzenes in Friedel-Crafts alkylation?
A) Fluorobenzene > Chlorobenzene > Bromobenzene > Iodobenzene
B) Iodobenzene > Bromobenzene > Chlorobenzene > Fluorobenzene
C) Chlorobenzene > Bromobenzene > Fluorobenzene > Iodobenzene
D) All halobenzenes react at the same rate.
42. Compared to Friedel-Crafts alkylation, Friedel-Crafts acylation is generally preferred because:
A) It is less exothermic.
B) It does not suffer from polyacylation due to the deactivating nature of the acyl group.
C) It uses milder catalysts.
D) It directly introduces a hydroxyl group onto the ring.
43. The reaction of benzene with acetyl chloride in the presence of AlCl₃ yields:
A) Ethylbenzene
B) Acetophenone
C) Benzaldehyde
D) Benzoic acid
44. In Friedel-Crafts acylation, what is the electrophile generated?
A) An alkyl carbocation
B) An acylium ion
C) A protonated acyl halide
D) A free radical
45. What is the main limitation of Friedel-Crafts alkylation regarding polyalkylation?
A) The alkyl group is deactivating, preventing further reaction.
B) The alkyl group is activating, making the product more reactive than the starting material.
C) The catalyst is consumed during the reaction, requiring excess.
D) The reaction is reversible and favors the starting materials.
46. Friedel-Crafts alkylation is generally not suitable for the alkylation of which type of aromatic compound?
A) Benzene
B) Toluene
C) Aniline
D) Naphthalene
47. Which of the following is a common Lewis acid catalyst used in Friedel-Crafts reactions?
A) H₂SO₄
B) NaOH
C) FeCl₃
D) NH₃
48. In Friedel-Crafts alkylation, what is the primary role of the Lewis acid catalyst (e.g., AlCl₃)?
A) To protonate the alkyl halide
B) To abstract a halide ion from the alkyl halide, generating a carbocation
C) To activate the aromatic ring towards electrophilic attack
D) To neutralize the acidic byproducts
49. Which type of catalyst is typically used in Friedel-Crafts alkylation and acylation reactions?
A) Protic acids
B) Lewis acids
C) Brønsted-Lowry bases
D) Organocatalysts
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