Question

Given below are two statements. One is labelled as Assertion A and the other is labelled as Reason R.
Assertion A : [6] Annulene. [8] Annulene and cis -[10] Annulene, are respectively aromatic, not-aromatic and aromatic.

Reason R : Planarity is one of the requirements of aromatic systems.
In the light of the above statements, choose the most appropriate answer from the options given below.

• A. Both A and R are correct and R is the correct explanation of A.
• B. Both A and R are correct but R is NOT the correct explanation of A.
• C. A is correct but R is not correct.
• D. A is not correct but R is correct.

Answer 1

Answer: (A)

Assertion A : Not correct , Reason R : correct

In [10] -Annulene - the hydrogen atoms in the 1 and 6 position interfere with each other and force the molecule out of planarity

If this annulene with five cis double bonds were planar, each internal angle would be $144^{\circ }$. Since a normal double bond has bond angle of $120^{\circ }$, this would be from ideal. This compound can be made but it does not adopt a planar conformation and therefore is not aromatic even though it has ten $\pi$ electrons.