Question

Among the following, the aromatic compounds are:

• A. $\mathrm{A}$ and $\mathrm{B}$ only
• B. $\mathrm{A}$, $\mathrm{B}$and $\mathrm{C}$ only
• C. $\mathrm{B}$, $\mathrm{C}$ and $\mathrm{D}$ only
• D. $\mathrm{B}$and $\mathrm{C}$ only

Answer 1

The correct option is D

$\mathrm{B}$and $\mathrm{C}$ only

An explanation for correct option:

(D) $\mathbf{B}$ and $\mathbf{C}$only

1. The molecules which follow huckel's rule of aromaticity are said to be aromatic in nature.
2. Huckel's rule states that 'a molecule is said to be aromatic if it is planar, cyclic and has $\left(4\mathrm{n}+2\right)\mathrm{\pi }$ electrons where n is a non-negative integer.
3. Compounds $\mathrm{B}$ in the question is Benzene.
4. It is cyclic, planar and it has $6\pi$ electrons which can be represented by using huckel's rule.
5. So, with $\left(n=1\right)$ : $\left(4\times 1+2\right)\pi =6\pi$
6. Compound $\mathrm{C}$ in the question is Cyclopentadienyl anion.
7. It is cyclic, planar and has $6\pi$ electrons which can be represented by huckel's rule.
8. So, with $\left(n=1\right)$ : $\left(4\times 1+2\right)\pi =6\pi$
9. As, compounds $\mathrm{B}$ and $\mathrm{C}$ follow huckel's rule hence, they are aromatic compounds.

Explanation for incorrect options:

(A) $\mathbf{A}$ and $\mathbf{B}$ only

1. Compound $\mathrm{A}$ is cyclic, planar and has $4\pi$ electrons.
2. The number of $\pi$-electrons present in this compound does not represent huckle's rule hence, it is non-aromatic.

(B) $\mathbf{A}$, $\mathbf{B}$ and $\mathbf{C}$ only

Only compound $\mathrm{B}$ and $\mathrm{C}$ are aromatic in this option. $\mathrm{A}$ is a non-aromatic compound.

(C) $\mathbf{B}$, $\mathbf{C}$ and $\mathbf{D}$ only

1. Compound $\mathrm{D}$ is cyclic, planar and has $4\pi$ electrons.
2. The number of $\pi$-electrons present in this compound does not represent huckle's rule hence, it is non-aromatic.
3. Only compounds $\mathrm{B}$ and $\mathrm{C}$ are aromatic in this option. $\mathrm{D}$ is a non-aromatic compound.

Hence, option $\mathbf{D}$ is correct, compounds $\mathrm{B}$ and $\mathrm{C}$ are aromatic in nature.