TRB PG Assistant - Aromaticity in benzenoid and non‑benzenoid systems and related reactions One Line Questions & Answers

1. Which functional group is typically activating towards electrophilic aromatic substitution and is an ortho, para director? — -OCH3 (methoxy)

2. Which functional group is typically deactivating towards electrophilic aromatic substitution? — -NO2 (nitro)

3. According to Hückel's Rule, an aromatic system must have how many pi electrons? — 4n + 2

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

5. The cyclopentadienyl anion (C5H5-) is aromatic because it has: — 6 pi electrons.

6. The tropylium cation (C7H7+) is aromatic because it has: — 6 pi electrons and is planar.

7. Cyclooctatetraene is considered antiaromatic because it has: — 8 pi electrons and is non-planar.

8. In electrophilic aromatic substitution, the electrophile attacks: — The pi electron cloud.

9. The Wheland intermediate (arenium ion) in electrophilic aromatic substitution is: — A non-aromatic carbocation intermediate.

10. The stability of benzene compared to hypothetical hypothetical cyclohexatriene is quantified by its: — Resonance energy

11. What is the characteristic reaction of aromatic compounds? — Electrophilic aromatic substitution

12. Which statement about aromaticity is FALSE? — All aromatic compounds contain alternating single and double bonds.

13. Which of the following would be the most deactivated towards electrophilic aromatic substitution? — Nitrobenzene

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

15. 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: — Antiaromatic

16. What is the name of the bicyclic aromatic hydrocarbon with 10 pi electrons? — Naphthalene

17. Which of the following is an example of a non-aromatic compound? — Cyclohexane

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

19. Which rule dictates the number of pi electrons required for aromaticity? — Hückel's Rule

20. Which type of catalyst is typically used in the halogenation of benzene? — Lewis acid

21. The intermediate formed during electrophilic aromatic substitution is called: — Arenium ion (or sigma complex)

22. Nitration of benzene typically uses a mixture of concentrated nitric acid and: — Concentrated H2SO4

23. The Birch reduction of benzene leads to: — 1,4-Cyclohexadiene

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

25. Which of the following is an example of a fused ring aromatic system? — Naphthalene

26. Which of the following is an example of a benzenoid aromatic compound? — Benzene

27. Sulfonation of benzene can be reversed by treatment with: — Steam

28. Which of the following is a common reaction used to remove a sulfonic acid group from a benzene ring? — Heating with dilute sulfuric acid

29. In pyridine, the nitrogen atom contributes to aromaticity by: — Having its lone pair in an sp2 orbital within the plane of the ring.

30. Which reaction involves the introduction of an acyl group (-COR) onto the benzene ring? — Friedel-Crafts acylation

31. Which Lewis acid is commonly used as a catalyst in Friedel-Crafts alkylation? — AlCl3

32. The delocalization of pi electrons in aromatic systems leads to: — Increased stability.

33. Halogens (-Cl, -Br, -I) are deactivating but ortho, para directors in electrophilic aromatic substitution due to: — Inductive electron withdrawal and resonance electron donation.

34. The compound pyridine is considered aromatic because: — It is planar, cyclic, and has 6 pi electrons (including the lone pair on nitrogen).

35. Friedel-Crafts acylation is often preferred over alkylation because: — The acyl group is deactivating, preventing polyacylation.

36. What is the primary criterion for a compound to be aromatic? — It must be planar and possess a cyclic delocalized pi electron system.

37. Friedel-Crafts alkylation is generally not preferred for introducing secondary or tertiary alkyl groups because of: — Carbocation rearrangement.

38. The order of reactivity of benzene and its derivatives towards electrophilic substitution, with activating groups, is generally: — More reactive than benzene

39. The order of reactivity of benzene and its derivatives towards electrophilic substitution, with deactivating groups, is generally: — Less reactive than benzene

40. Which of the following is an example of a non-benzenoid aromatic compound? — Cyclopentadienyl anion

41. The resonance energy of aromatic compounds is: — Positive, indicating extra stability.

42. Which reaction is used to introduce a halogen onto the benzene ring? — Halogenation

43. Which of the following is a characteristic of antiaromatic compounds? — Planar, cyclic, 4n pi electrons, low stability.

44. Which of the following is NOT a characteristic of aromatic compounds? — High reactivity towards addition reactions

45. Which of the following conditions is essential for a cyclic compound to exhibit aromaticity? — Planarity of the ring system.

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

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

48. What is the primary driving force for the stability of aromatic compounds? — Delocalization of pi electrons

49. The regioselectivity of electrophilic aromatic substitution on monosubstituted benzenes is determined by: — The electronic and steric nature of the substituent.

50. Which of the following is a characteristic of heteroaromatic compounds like furan or thiophene? — They follow Hückel's rule for aromaticity, with heteroatoms contributing electrons to the pi system.

Aromaticity in benzenoid and non‑benzenoid systems and related reactions - One Line Questions