Question

Which out of the following is not aromatic compounds?

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

In option(a), cyclobutadiene is cyclic, planar, $4\pi$ electron's system follows (4n) pi electrons rule. So it is anti-aromatic.

In option (b), the structure is cyclic, planar, 6 electrons system ($4\pi \stackrel{-}{e}+2\stackrel{-}{e}$ from one of the lone pair of the O). It follows (4n+2) rule (n=2). $4\pi \stackrel{-}{e}and2\stackrel{-}{e}$ from lone pair are in complete delocalisation or in resonance, hence aromatic.

In option (c), the structure naphthalene is cyclic, planar, $10\pi \stackrel{-}{e}$ system, follows (4n+2) rule, hence aromatic.

In option (d), the structure pyridine is cyclic, planar, $6\pi \stackrel{-}{e}$ system, follows (4n+2) rule, hence aromatic. Here the lone pair electrons does not participate in delocalisation/conjugation.

So, the correct answer is option(a).