Recall the conditions for aromaticity

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

1. It is cyclic.
2. It is fully conjugated.
3. It is planar.
4. It has $(4n+2)\pi$ electrons (Hückel rule).

If planarity/full conjugation is lost, the compound is non-aromatic. If it is planar and conjugated but has $4n\pi$ electrons, it is antiaromatic.

Examine the compounds in the Assertion

(i) $[6]$ Annulene

$[6]$ Annulene is benzene. It is planar, fully conjugated, and has $6\pi$ electrons. Since $6 = 4n+2$ for $n=1$, it is aromatic.

So the first part is correct.

(ii) $[8]$ Annulene

$[8]$ Annulene has $8\pi$ electrons. If it were planar, it would be antiaromatic $(4n,\ n=2)$. To avoid this, it adopts a non-planar tub-shaped structure, so continuous overlap is lost. Therefore, it is not aromatic (non-aromatic).

So the second part is correct.

(iii) cis-$[10]$ Annulene

A $[10]$ annulene has $10\pi$ electrons, which satisfies Hückel rule: $10 = 4n+2 \quad (n=2)$ However, cis-$[10]$ annulene is not planar because of steric repulsion between inner hydrogens, so it cannot achieve the required continuous planar conjugation. Hence, cis-$[10]$ annulene is not aromatic.

Therefore, the statement saying that cis-$[10]$ annulene is aromatic is incorrect.

So the overall Assertion A is false.

Examine the Reason

Reason R states: Planarity is one of the requirements of aromatic systems.

This is a standard condition for aromaticity, so R is correct.

Choose the correct option

• Assertion A: Not correct
• Reason R: Correct

Therefore, the correct option is:

D: A is not correct but R is correct.

Comparison with stored answer

Stored correct answer: D

My derived answer: D

They agree.