JEE Main - Aromatic hydrocarbons benzene structure aromaticity and electrophilic substitution Question Bank with Options

1. What is the electrophile in the bromination of benzene using Br2 and FeBr3?

A) Br-

B) Br+

C) FeBr3

D) HBr

2. The relative ease of electrophilic substitution of benzene compared to addition to alkenes is explained by:

A) Higher electron density in benzene

B) Greater stability of the intermediate arenium ion

C) Loss of aromaticity during addition

D) Formation of a more stable product

3. Which type of reaction is favored by aromatic hydrocarbons due to their stable delocalized pi electron system?

A) Addition reactions

B) Substitution reactions

C) Elimination reactions

D) Rearrangement reactions

4. The structure of benzene was proposed by:

A) Dmitri Mendeleev

B) August Kekulé

C) Michael Faraday

D) Svante Arrhenius

5. Which of the following is a deactivating group due to resonance effect?

A) -OH

B) -NH2

C) -Cl

D) -NO2

6. The loss of a proton from the arenium ion in electrophilic substitution of benzene restores:

A) The positive charge on the ring

B) The aromaticity of the ring

C) The delocalized pi system

D) Both B and C

7. Which of the following is a correct representation of a resonance structure of benzene?

A) A structure with localized double bonds at 1,2, 3,4, 5,6 positions

B) A structure with a single C-C bond and a single C=C bond

C) Two structures with alternating single and double bonds that are equivalent

D) A structure with all C-C bonds of equal length and strength

8. What is the limiting factor for the number of pi electrons in Hückel's rule for aromaticity?

A) The number of carbon atoms in the ring

B) The total number of pi electrons must be 4n

C) The total number of pi electrons must be 4n+2

D) The presence of at least one double bond

9. The product of the Friedel-Crafts alkylation of benzene with ethyl chloride and AlCl3 can undergo:

A) Isomerization to propylbenzene

B) Polyalkylation

C) Rearrangement of the ethyl group to isopropyl

D) All of the above

10. In the electrophilic substitution of toluene, the methyl group is:

A) Deactivating and meta-directing

B) Activating and meta-directing

C) Deactivating and ortho, para-directing

D) Activating and ortho, para-directing

11. Which reaction is used to convert benzene to nitrobenzene?

A) Reaction with N2O4 and H2SO4

B) Reaction with NO2+ and H2SO4

C) Reaction with HNO3 and H2SO4

D) Reaction with NO and H2SO4

12. The stability of benzene is attributed to:

A) Localized pi bonds

B) Steric hindrance

C) Resonance and delocalization of pi electrons

D) Strong sigma bonds

13. The mechanism of electrophilic substitution in benzene involves:

A) Attack by a nucleophile followed by loss of a proton

B) Attack by an electrophile to form a sigma complex, followed by loss of a proton

C) Addition of the electrophile across a double bond

D) Radical chain mechanism

14. Which of the following is an example of a non-benzenoid aromatic compound?

A) Toluene

B) Naphthalene

C) Cyclopentadienyl anion

D) Anthracene

15. The compound cyclopentadienyl anion is aromatic because it has:

A) 6 pi electrons

B) 4 pi electrons

C) 8 pi electrons

D) 10 pi electrons

16. Which of the following is a requirement for a compound to be considered aromatic according to Hückel's rule?

A) At least one double bond

B) A cyclic structure with 4n pi electrons

C) A planar ring system with a delocalized (4n+2) pi electron cloud

D) Presence of heteroatoms in the ring

17. The electrophilic substitution reaction that introduces an acyl group (-COR) onto the benzene ring is called:

A) Friedel-Crafts alkylation

B) Friedel-Crafts acylation

C) Electrophilic acylation

D) Aromatic acylation

18. What is the electrophile generated in the Friedel-Crafts acylation of benzene?

A) R-C=O+

B) R-C-O-

C) R-C+

D) R-O+

19. Which of the following is a consequence of the aromaticity of benzene?

A) It readily undergoes addition reactions like alkenes

B) It is less stable than hypothetical 1,3,5-cyclohexatriene

C) It has a lower heat of hydrogenation compared to cyclohexene

D) It reacts via electrophilic substitution rather than addition

20. The resonance energy of benzene is approximately:

A) 36 kJ/mol

B) 72 kJ/mol

C) 150 kJ/mol

D) 360 kJ/mol

21. The energy released when two moles of H2 are added to benzene to form cyclohexane is called:

A) Activation energy

B) Resonance energy

C) Heat of hydrogenation

D) Heat of formation

22. The term 'aromatic' originally referred to:

A) Compounds with a strong odor

B) Compounds with a planar structure

C) Compounds with a delocalized electron system

D) Compounds that undergo substitution reactions

23. Which of the following is an example of an aromatic hydrocarbon?

A) Ethane

B) Ethene

C) Benzene

D) Cyclohexene

24. Aromaticity in benzene is due to:

A) The presence of only sigma bonds

B) The overlap of sp3 hybridized orbitals

C) The cyclic arrangement of sp2 hybridized carbons with a delocalized pi system of 6 electrons

D) The presence of alternating single and double bonds

25. The Kekulé structure of benzene proposes:

A) A planar hexagonal ring with delocalized pi electrons

B) A planar hexagonal ring with two resonance structures showing alternating single and double bonds

C) A non-planar structure with sp3 hybridized carbons

D) A linear arrangement of carbon atoms

26. What is the product of the reaction of benzene with CH3Cl in the presence of AlCl3?

A) Chlorobenzene

B) Toluene

C) Xylene

D) Benzene

27. The order of reactivity of benzene towards different electrophilic substitution reactions is generally:

A) Nitration > Halogenation > Friedel-Crafts > Sulfonation

B) Friedel-Crafts > Halogenation > Nitration > Sulfonation

C) Sulfonation > Nitration > Halogenation > Friedel-Crafts

D) Halogenation > Nitration > Friedel-Crafts > Sulfonation

28. The presence of an electron-withdrawing group on the benzene ring generally:

A) Activates the ring and directs ortho, para

B) Deactivates the ring and directs meta

C) Activates the ring and directs meta

D) Deactivates the ring and directs ortho, para

29. The presence of an electron-donating group on the benzene ring generally:

A) Deactivates the ring and directs meta

B) Activates the ring and directs ortho, para

C) Deactivates the ring and directs ortho, para

D) Activates the ring and directs meta

30. Which of the following groups is a deactivating and meta-directing group in electrophilic aromatic substitution?

A) -NH2

B) -OCH3

C) -CHO

D) -CH3

31. Which of the following groups is an activating and ortho, para-directing group in electrophilic aromatic substitution?

A) -NO2

B) -CN

C) -OH

D) -SO3H

32. The reaction where benzene reacts with a halogen in the presence of a Lewis acid catalyst is called:

A) Halogenation

B) Electrophilic halogenation

C) Friedel-Crafts halogenation

D) Aromatic halogenation

33. In the sulfonation of benzene, the electrophile is:

A) SO3

B) H2SO4

C) SO3H+

D) SO2

34. Carbocation rearrangements can occur during Friedel-Crafts alkylation due to:

A) The stability of the primary carbocation

B) The formation of a stable arenium ion

C) The tendency of carbocations to rearrange to more stable forms

D) The presence of the Lewis acid catalyst

35. Which of the following is a common Lewis acid catalyst used in Friedel-Crafts reactions?

A) H2SO4

B) NaOH

C) AlCl3

D) HCl

36. The Friedel-Crafts alkylation of benzene requires:

A) An alcohol and a strong acid

B) An alkyl halide and a Lewis acid catalyst

C) An alkene and a Brønsted acid

D) An alkyl halide and a strong base

37. What is the role of concentrated sulfuric acid in the nitration of benzene using nitric acid?

A) To act as a solvent

B) To provide the electrophile (NO2+)

C) To absorb water produced

D) To increase the solubility of nitric acid

38. Which of the following is a common electrophile used in the nitration of benzene?

A) NO3-

B) NO2+

C) HNO3

D) H2O

39. The intermediate formed during the electrophilic substitution of benzene is known as:

A) Carbanion

B) Carbocation

C) Arenium ion (or sigma complex)

D) Free radical

40. In electrophilic substitution of benzene, the attacking species is an:

A) Electron-rich species

B) Electron-deficient species

C) Free radical

D) Proton donor

41. Which of the following reactions is characteristic of aromatic hydrocarbons like benzene?

A) Electrophilic addition

B) Nucleophilic addition

C) Electrophilic substitution

D) Radical substitution

42. The delocalization of pi electrons in benzene is often represented by:

A) Two distinct resonance structures with localized double bonds

B) A single structure with alternating single and double bonds

C) A circle inside a hexagon

D) A hexagon with only single bonds

43. What is the hybridization of each carbon atom in the benzene ring?

A) sp

B) sp2

C) sp3

D) d2sp3

44. The bond length between carbon atoms in benzene is:

A) Shorter than a typical C-C single bond

B) Longer than a typical C=C double bond

C) Intermediate between a C-C single bond and a C=C double bond

D) Equal to the bond length in cyclohexane

45. Which of the following is NOT an aromatic compound?

A) Benzene

B) Naphthalene

C) Cyclohexane

D) Pyridine

46. The resonance structures of benzene contribute to its:

A) Instability

B) Reactivity towards addition

C) Delocalized electron cloud and stability

D) Alternating single and double bond character

47. Hückel's rule states that for a compound to be aromatic, it must possess a planar ring system with (4n+2) pi electrons, where 'n' is:

A) A positive integer

B) A non-negative integer

C) An even integer

D) An odd integer

48. Which of the following is a characteristic of aromatic compounds?

A) Undergo addition reactions readily

B) Contain a delocalized pi electron system

C) Are typically saturated hydrocarbons

D) Have a planar ring structure with alternating single and double bonds

49. What is the molecular formula of benzene?

A) C6H5

B) C6H6

C) C5H6

D) C6H12

Aromatic hydrocarbons benzene structure aromaticity and electrophilic substitution - Question Bank