Question

Which of the following compounds are anti-aromatic in nature?

• A. Naphthalene
• B. Cyclopentadienyl cation
• C. butadiene
• D. Cyclooctatetraene
  

Answer 1

The correct option is B Cyclopentadienyl cation

Naphthalene is aromatic in nature because it nearly follows all the tenets of Huckel's rules for aromaticity. It has $[4n+2]\pi$ electrons and they are delocalized to a good extent, maybe not as much as found in benzene (or other monocyclic aromatic compounds).

Cyclooctatetraene is non-aromatic in nature. Despite possessing $\left[4n\pi \right]$ electrons, it is not planar, and hence is non-aromatic. Butadiene is not a cyclic molecule. Cyclopentadienyl cation is anti-aromatic because, apart from delocalisation, it possess $\left[4n\pi \right]$ electrons.