Question

Identify the odd one out from the following.
A. ${{\rm{C}}_{\rm{6}}}{{\rm{H}}_{\rm{6}}}$ Benzene

B. ${{\rm{C}}_{\rm{4}}}{{\rm{H}}_{\rm{8}}}$ Cyclobutane

C. ${{\rm{C}}_{\rm{5}}}{{\rm{H}}_{{\rm{10}}}}$ Cyclopentane

D. ${{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}$ Cyclohexane

Answer 1

We know that, if a compound is planar, cyclic, conjugated and follows Huckel’s rule of aromaticity, that is, 4n+2 pi electrons, then the compound is aromatic. To identify the odd one, we have to check the aromatic character of all the compounds.

Complete step by step answer: Let’s discuss the aromatic character of all the compounds given in the options.
Option A is benzene $\left( {{{\rm{C}}_{\rm{6}}}{{\rm{H}}_{\rm{6}}}} \right)$. We know the structure of benzene that is,

The number of pi electrons in the compound is 6. So, it follows the Huckel’s rule of aromaticity $\left( {4n + 2} \right)$ for n=2. Therefore, benzene is an aromatic compound.

Now, we will discuss the aromatic character of cyclobutane. The structure of cyclobutane is

So, from the figure it is clear that no double bond exists, that means, no pi electrons. No pi electrons indicate that the compound is non aromatic.

Now, we will discuss the aromatic character of cyclopentane. The structure of cyclopentane is,

In cyclohexane no double bonds are present. This indicates the absence of pi electrons in the compound. Therefore, cyclohexane is also a non-aromatic compound.

So, we get to know that benzene is aromatic and all other compounds are non-aromatic. Therefore, the correct option is A, that is, benzene.

So, the correct answer is “Option A”.

Note: There are two terms antiaromatic and non-aromatic. If a compound is planar, cyclic, conjugated and follows 4n pi electrons, then the compound is antiaromatic. Non aromatic compounds are those compounds that do not belong to both aromatic compounds and antiaromatic compounds.