Q.15 The non-aromatic compound/ion is:

Aromaticity 

A compound is aromatic if it satisfies all of the following:

1. Cyclic

2. Planar

3. Fully conjugated

4. Follows Hückel’s rule → (4n + 2) π electrons

If a compound is:

• Cyclic, planar, conjugated but has 4n π electrons → Antiaromatic

• Fails cyclic/planar/conjugation → Non-aromatic

Correct Answer

(D)

Explanation of Each Option

Option (A): Naphthalene

• Two fused benzene rings

• Fully conjugated and planar

• Total π electrons = 10

• Follows 4n + 2 rule (n = 2)

Aromatic compound

Option (B): Tropylium Cation (C₇H₇⁺)

• Cyclic and planar

• Fully conjugated

• π electrons = 6

• Follows Hückel’s rule

Aromatic ion

Option (C): Cyclooctatetraene Dianion (C₈H₈²⁻)

• 4 double bonds + 2 extra electrons

• Total π electrons = 10

• Becomes planar after gaining electrons

• Follows 4n + 2 rule

Aromatic ion

Option (D): Cyclopentadienyl Cation (C₅H₅⁺)

• Cyclic and conjugated

• π electrons = 4

• Follows 4n rule (n = 1)

Antiaromatic → chemically unstable

 Since antiaromatic species are not aromatic, this ion is classified as:

Non-aromatic

Final Conclusion

Correct Answer: (D)