TRB PG Assistant - Aromaticity in benzenoid and non‑benzenoid systems and related reactions Online Test (MCQ Quiz)

1. What is the primary criterion for a compound to be aromatic?

A) It must contain a benzene ring. B) It must be planar and possess a cyclic delocalized pi electron system. C) It must undergo electrophilic substitution reactions. D) It must have alternating single and double bonds.

2. Which rule dictates the number of pi electrons required for aromaticity?

A) Boyle's Law B) Hückel's Rule C) Ohm's Law D) Avogadro's Law

3. According to Hückel's Rule, an aromatic system must have how many pi electrons?

A) 2n B) 4n + 2 C) 2n + 1 D) 4n

4. Which of the following is an example of a benzenoid aromatic compound?

A) Cyclopentadiene B) Tropylium cation C) Benzene D) Cyclooctatetraene

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

A) Naphthalene B) Anthracene C) Cyclopentadienyl anion D) Phenanthrene

6. What is the number of pi electrons in benzene?

A) 4 B) 6 C) 8 D) 10

7. The tropylium cation (C7H7+) is aromatic because it has:

A) 6 pi electrons and is planar. B) 8 pi electrons and is planar. C) 10 pi electrons and is planar. D) 4 pi electrons and is planar.

8. Cyclooctatetraene is considered antiaromatic because it has:

A) 6 pi electrons and is planar. B) 8 pi electrons and is planar. C) 8 pi electrons and is non-planar. D) 10 pi electrons and is planar.

9. What is the characteristic reaction of aromatic compounds?

A) Addition reactions B) Elimination reactions C) Electrophilic aromatic substitution D) Nucleophilic addition

10. Which of the following conditions is essential for a cyclic compound to exhibit aromaticity?

A) Presence of a heteroatom in the ring. B) Planarity of the ring system. C) Presence of only sp2 hybridized carbons. D) Alternating single and double bonds in the ring.

11. The delocalization of pi electrons in aromatic systems leads to:

A) Increased reactivity. B) Decreased stability. C) Increased stability. D) Alternating bond lengths.

12. Which of the following is NOT a characteristic of aromatic compounds?

A) Planarity B) Cyclic structure C) Delocalized pi electron system D) High reactivity towards addition reactions

13. What is the name of the bicyclic aromatic hydrocarbon with 10 pi electrons?

A) Benzene B) Naphthalene C) Anthracene D) Pyrene

14. The cyclopentadienyl anion (C5H5-) is aromatic because it has:

A) 4 pi electrons. B) 6 pi electrons. C) 8 pi electrons. D) 10 pi electrons.

15. Which Lewis acid is commonly used as a catalyst in Friedel-Crafts alkylation?

A) H2SO4 B) AlCl3 C) HCl D) HNO3

16. In electrophilic aromatic substitution, the electrophile attacks:

A) A sigma bond. B) The pi electron cloud. C) A lone pair of electrons. D) An anti-bonding orbital.

17. The intermediate formed during electrophilic aromatic substitution is called:

A) Carbanion B) Carbocation C) Arenium ion (or sigma complex) D) Free radical

18. Which functional group is typically deactivating towards electrophilic aromatic substitution?

A) -OH (hydroxyl) B) -NH2 (amino) C) -NO2 (nitro) D) -CH3 (methyl)

19. Which functional group is typically activating towards electrophilic aromatic substitution and is an ortho, para director?

A) -COOH (carboxyl) B) -SO3H (sulfonic acid) C) -Cl (chloro) D) -OCH3 (methoxy)

20. Halogens (-Cl, -Br, -I) are deactivating but ortho, para directors in electrophilic aromatic substitution due to:

A) Inductive effect only. B) Resonance effect only. C) Inductive electron withdrawal and resonance electron donation. D) Steric hindrance.

21. Nitration of benzene typically uses a mixture of concentrated nitric acid and:

A) Concentrated HCl B) Concentrated H2SO4 C) Concentrated H3PO4 D) Concentrated CH3COOH

22. Sulfonation of benzene can be reversed by treatment with:

A) Dilute acid B) Dilute alkali C) Steam D) Heat

23. Friedel-Crafts alkylation is generally not preferred for introducing secondary or tertiary alkyl groups because of:

A) Lack of reactivity. B) Carbocation rearrangement. C) Polyalkylation. D) Deactivation of the ring.

24. Which reaction is used to introduce a halogen onto the benzene ring?

A) Nitration B) Sulfonation C) Halogenation D) Friedel-Crafts acylation

25. The order of reactivity of benzene and its derivatives towards electrophilic substitution, with activating groups, is generally:

A) Less reactive than benzene B) More reactive than benzene C) Equally reactive as benzene D) Non-reactive

26. The order of reactivity of benzene and its derivatives towards electrophilic substitution, with deactivating groups, is generally:

A) More reactive than benzene B) Less reactive than benzene C) Equally reactive as benzene D) Non-reactive

27. Which of the following is an example of a fused ring aromatic system?

A) Cyclopentadiene B) Tropylium cation C) Naphthalene D) Cyclooctatetraene

28. A compound that has the same number of pi electrons as benzene (6 pi electrons) but is not a benzene derivative is:

A) Cyclooctatetraene B) Cyclopentadienyl anion C) Tropylium cation D) Naphthalene

29. Which reaction involves the introduction of an acyl group (-COR) onto the benzene ring?

A) Friedel-Crafts alkylation B) Friedel-Crafts acylation C) Nitration D) Halogenation

30. Friedel-Crafts acylation is often preferred over alkylation because:

A) It is simpler to perform. B) The acyl group is deactivating, preventing polyacylation. C) It does not require a Lewis acid catalyst. D) It leads to carbocation rearrangements.

31. What is the primary driving force for the stability of aromatic compounds?

A) Sigma bond strength B) Pi bond strength C) Delocalization of pi electrons D) Steric strain relief

32. A compound that is planar, cyclic, has 4n pi electrons, and is expected to be unstable compared to benzene is called:

A) Aromatic B) Non-aromatic C) Antiaromatic D) Pseudoaromatic

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

A) Benzene B) Cyclopentadiene C) Cyclohexane D) Tropylium cation

34. The resonance energy of aromatic compounds is:

A) Negative, indicating instability. B) Zero, indicating no extra stability. C) Positive, indicating extra stability. D) Variable and dependent on substituents.

35. Which of the following is a characteristic of antiaromatic compounds?

A) Planar, cyclic, 4n pi electrons, high stability. B) Planar, cyclic, 4n+2 pi electrons, high stability. C) Planar, cyclic, 4n pi electrons, low stability. D) Non-planar, cyclic, 4n+2 pi electrons, high stability.

36. The compound pyridine is considered aromatic because:

A) It contains a benzene ring. B) It is planar, cyclic, and has 6 pi electrons (including the lone pair on nitrogen). C) It is planar, cyclic, and has 10 pi electrons. D) It undergoes addition reactions readily.

37. In pyridine, the nitrogen atom contributes to aromaticity by:

A) Donating one electron to the pi system. B) Participating in sigma bonding. C) Having its lone pair in an sp2 orbital perpendicular to the pi system. D) Having its lone pair in an sp2 orbital within the plane of the ring.

38. Which type of catalyst is typically used in the halogenation of benzene?

A) Brønsted acid B) Lewis acid C) Oxidizing agent D) Reducing agent

39. The regioselectivity of electrophilic aromatic substitution on monosubstituted benzenes is determined by:

A) The catalyst used. B) The strength of the electrophile. C) The electronic and steric nature of the substituent. D) The solvent used.

40. A compound that is cyclic, planar, and has delocalized pi electrons, but does not follow Hückel's rule (e.g., 8 pi electrons) would be classified as:

A) Aromatic B) Antiaromatic C) Non-aromatic D) Heteroaromatic

41. Which of the following is a common reaction used to remove a sulfonic acid group from a benzene ring?

A) Dilute acid hydrolysis B) Steam distillation C) Heating with dilute sulfuric acid D) Reaction with NaOH

42. Which of the following is an example of a fused polycyclic aromatic hydrocarbon (PAH)?

A) Benzene B) Toluene C) Pyrene D) Cyclohexane

43. The stability of benzene compared to hypothetical hypothetical cyclohexatriene is quantified by its:

A) Activation energy B) Enthalpy of formation C) Resonance energy D) Heat of combustion

44. Which of the following would be the most deactivated towards electrophilic aromatic substitution?

A) Aniline B) Phenol C) Nitrobenzene D) Toluene

45. The Wheland intermediate (arenium ion) in electrophilic aromatic substitution is:

A) A stable aromatic species. B) A non-aromatic carbocation intermediate. C) A transition state. D) A radical species.

46. Which statement about aromaticity is FALSE?

A) All aromatic compounds are cyclic. B) All aromatic compounds are planar. C) All aromatic compounds contain alternating single and double bonds. D) Aromatic compounds have enhanced stability due to electron delocalization.

47. The reaction of benzene with a diazonium salt in the presence of a base is known as:

A) Sandmeyer reaction B) Gattermann reaction C) Azo coupling D) Fries rearrangement

48. Which of the following is a characteristic of heteroaromatic compounds like furan or thiophene?

A) They are always non-aromatic. B) They follow Hückel's rule for aromaticity, with heteroatoms contributing electrons to the pi system. C) They contain only carbon atoms in the ring. D) They undergo nucleophilic substitution reactions exclusively.

49. The Birch reduction of benzene leads to:

A) Cyclohexane B) Cyclohexene C) 1,4-Cyclohexadiene D) Phenol

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

A) Pyridine B) Furan C) Pyrrole D) Thiophene

Aromaticity in benzenoid and non‑benzenoid systems and related reactions - Online Test

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