Question

Which of the following are aromatic?

• A. A) Cyclopropenone
• B. B) Tropone
• C. C) Squaric acid
• D. D) Cyclohexenone

Answer 1

Answer: (A), (B), (C)

A, B, C

Answer 2

To determine aromaticity, we check for the following criteria: 1. Cyclic, 2. Planar, 3. Continuous ring of delocalized pi electrons, 4. Huckel's Rule ($4n+2$ pi electrons).

• A) Cyclopropenone: Cyclic, planar, 2 $\pi$ electrons (from C=C). Fits $4n+2$ ($n=0$). Aromatic.
• B) Tropone: Cyclic, planar, 6 $\pi$ electrons (from 3 C=C bonds). Fits $4n+2$ ($n=1$). Aromatic.
• C) Squaric acid: Cyclic, planar, 6 $\pi$ electrons (from 1 C=C and 2 C=O). Fits $4n+2$ ($n=1$). Aromatic.
• D) Cyclohexenone: Cyclic, not fully planar, 4 $\pi$ electrons (from 1 C=C and 1 C=O). Fits $4n$ ($n=1$). Non-aromatic.