Question

Among the following, the anti-aromatic compound(s) is (are)

• A. A
• B. B
• C. C
• D. D

Hint:

Remember: $(4n + 2)$ → aromatic, $4n$ → anti-aromatic, and nonplanar systems are non-aromatic.

Answer 1

The Correct Option is B, C, D

Step 1: Recall Hückel’s rule.
A compound is: - Aromatic if it has $(4n + 2)$ π-electrons (planar, cyclic, conjugated)
- Anti-aromatic if it has $4n$ π-electrons (planar and conjugated)
Step 2: Analyze each structure.
(A) Cyclopentadienyl anion: 6 π-electrons → $(4n+2)$ form (n=1) → aromatic. ✗
(B) Cyclopentadienyl cation: 4 π-electrons → $4n$ form (n=1) → anti-aromatic. ✓
(C) Cyclopropenyl cation: 2 π-electrons → $(4n+2)$ form (n=0) → aromatic. ✗
(D) Cyclobutadiene: 4 π-electrons → $4n$ form (n=1) → anti-aromatic. ✓
Step 3: Conclusion.
Anti-aromatic compounds are (B) Cyclopentadienyl cation and (D) Cyclobutadiene.