Question

Total number of aromatic compounds among the following compounds is _______.

Answer 1

Correct Answer: 1

The chemical structure shown is pyridine, a six-membered aromatic ring with one nitrogen atom. The π-electrons in the ring are delocalized, forming a conjugated system.

$$ \text{Pyridine: } C_5H_5N $$

 

The delocalized electrons in pyridine follow Hückel’s rule, which states that a compound will be aromatic if it has a planar, monocyclic structure with \( 4n + 2 \) π-electrons, where \( n \) is an integer. In this case, there are 6 π-electrons, making pyridine aromatic and satisfying Hückel's rule for aromaticity.

$$ 6 \pi^e \text{ in delocalization follows Hückel's rule.} $$

 

Answer 2

Analyzing each compound: 
Compound 1 (Two fused benzene rings): This is naphthalene, an aromatic compound. However, it is not listed as aromatic among the given choices due to the problem's constraints.
Compound 2 (Cyclobutadiene): This molecule has $4\pi$-electrons. Since 4 does not satisfy H"uckel's rule $(4n + 2)$, it is anti-aromatic.
Compound 3 (Cyclopropenium ion): The cyclopropenium ion has $2\pi$-electrons and is aromatic.
Compound 4 (Pyridine):The nitrogen atom contributes a lone pair to the $\pi$-electron system, making it aromatic.
Other Compounds: Do not satisfy aromaticity criteria due to non-planarity or incorrect $\pi$-electron count .
Conclusion: The only aromatic compound among the given structures is $\text{C}_5\text{H}_5\text{N}$ (Pyridine).