Question

Explain why the following systems are not aromatic?

Answer 1

The given systems are not aromatic due to lack of localisation of $(4n+2)\pi$ electrons in the cyclic system.
For a molecule to be aromatic, $4n+2\pi$ electrons should be completely delocalized in the planar ring system.
For compounds (i) and (ii) only $4\pi$ electrons are present in the ring. For compound (III), $8\pi$ electrons are present in the ring.