Question

Which one of the following compounds is non-aromatic ? 

• A. A
• B. B
• C. C
• D. D

Hint:

Aromatic: Cyclic, Planar, Conjugated, $(4n+2)\pi\ e^-$.
Anti-aromatic: Cyclic, Planar, Conjugated, $(4n)\pi\ e^-$.
Non-aromatic: Fails any of the first three criteria (e.g., non-planar or non-cyclic).

Answer 1

The Correct Option is C

Step 1: Apply Hückel's Rule ($4n+2$) $\pi$ electrons for aromaticity.
Step 2: Furan and Thiophene have 6 $\pi$ electrons (4 from double bonds + 2 from lone pair), so they are aromatic.
Step 3: Cyclopropenyl cation has 2 $\pi$ electrons ($n=0$ in $4n+2$), so it is aromatic.
Step 4: Cyclobutadiene has 4 $\pi$ electrons. It follows the $4n$ rule, making it anti-aromatic, which falls under the broad category of "non-aromatic" in many MCQ contexts.