Organic Chemistry – Some Basic Principles and Techniques

Among the given organic compounds, the total number of aromatic compounds is [figure]

Answer

3

Solution

[figure]

(A): two ring-fusion C are sp³ (C–H) ⇒ cyclic conjugation broken ⇒ (A) is non-aromatic

(B): has a benzene ring (planar, 6 π e⁻) ⇒ (B) is aromatic

(C): planar, fully conjugated; lone pair in p orbital ⇒ 8 + 2 = 10 π e⁻ (4n + 2, n = 2) ⇒ (C) is aromatic

(D): planar, fully conjugated anion ⇒ 12 + 2 = 14 π e⁻ (4n + 2, n = 3) ⇒ (D) is aromatic

∵ Hückel rule: cyclic, planar, complete conjugation and (4n + 2) π electrons

Answer: 3