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

The Correct Option is D

To determine the correct answer to the question, let's examine both the assertion and the reason provided:

Assertion A: [6] Annulene, [8] Annulene, and cis-[10] Annulene, are respectively aromatic, non-aromatic, and aromatic.

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

1. Analyzing Assertion A:
   • [6] Annulene: This molecule is aromatic because it satisfies the Huckel's rule for aromaticity, which requires the molecule to have \(4n+2\) π electrons, where \(n\) is a non-negative integer. Here, for [6] annulene, \(n=1\) (as it has \(4(1)+2 = 6\) π electrons).
   • [8] Annulene: This molecule is non-aromatic. According to Huckel's rule, it would require 10 π electrons to be aromatic, but it only has 8, which does not satisfy the rule.
   • cis-[10] Annulene: This molecule is also non-aromatic because it cannot maintain planarity due to angle strain and steric hindrance. Although it has 10 π electrons, its inability to be planar disqualifies it as aromatic.
2. Analyzing Reason R:

Planarity is indeed one of the critical requirements for a compound to exhibit aromaticity. Aromatic compounds must have a cyclic, continuous overlap of p orbitals, which is only possible if the molecule is planar.

1. Conclusion: Since Assertion A is incorrect but Reason R is correct, the correct option is: A is not correct but R is correct.