Question

Identify the compound which is non-aromatic in nature.

• A. Compound [A]
• B. Compound [B]
• C. Compound [C]
• D. Compound [D]

Hint:

To check the aromaticity of heterocyclic compounds, ensure they have a conjugated system of electrons and satisfy the \(4n + 2\) rule for aromaticity.

Answer 1

The Correct Option is B

To determine which compound is non-aromatic, we need to check whether the compounds obey Hückel's rule for aromaticity, which states that for a compound to be aromatic, it must have a planar structure and a conjugated system of \(\pi\)-electrons that follows the \(4n + 2\) rule (where \(n\) is a non-negative integer). 
1. Compound [A]: - This is benzene (\(C_6H_6\)), which is aromatic as it has 6 \(\pi\)-electrons (\(n = 1\), thus \(4n + 2 = 6\)). 
2. Compound [B]: - This is furan, a heterocyclic compound with an oxygen atom in the ring. It has a conjugated system of 6 \(\pi\)-electrons, but one of these electrons comes from the oxygen lone pair. According to the rules for aromaticity, furan is not aromatic because it doesn’t follow the \(4n + 2\) rule perfectly in all conditions. Thus, it is non-aromatic. 
3. Compound [C]: - This is pyrrole, which is aromatic. It has 6 \(\pi\)-electrons (with the nitrogen lone pair participating), and it satisfies the \(4n + 2\) rule. 
4. Compound [D]: - This is thiophene, which is aromatic. It has 6 \(\pi\)-electrons from the sulfur lone pair and conjugation, fulfilling the \(4n + 2\) rule. Thus, the correct answer is (B) as furan is non-aromatic.