Question

Which of the following is aromatic in nature?

Answer 1

The aromatic compounds are those which have one more ring in its structure and it contains pi electrons which are delocalized all over the structure. Also, the aromaticity of a compound can be found with the help of Huckel’s rule. According to which a compound which contains $\left( {4n + 2} \right)$ pi electrons is considered in nature. Thus we will analyze each compound.
Formula Used:
For aromatic compounds, the number of pi electrons must be $\left( {4n + 2} \right)$, where n is an integer starting from zero.

Complete Answer:
Aromatic compounds are those compounds that contain one more ring and follow the Huckel rule of aromaticity. According to the Huckel rule of aromaticity, a planar ring molecule will be aromatic in nature when it contains a number of pi electrons in order of $\left( {4n + 2} \right)$. We will analyze each compound respectively. Each double bond constitutes two electrons and a negative charge also indicates two electrons.

Here the total number of electrons are $\left( {2 + 2 = 4} \right)$. Thus it is not in order of $\left( {4n + 2} \right)$, therefore it is not an aromatic compound.

Total number pi bond is one and it has a negative charge also which in total has $\left( {2 + 2 = 4} \right)$ electrons. Thus it is not in order of $\left( {4n + 2} \right)$, therefore it is not an aromatic compound.

Total number of pi bonds is four and it has a negative charge also. Therefore the total number of electrons is: $n = 2$ which is in the order of $\left( {4n + 2} \right)$ for $n = 2$. Hence it is an aromatic compound.

Here the total number of electrons are $\left( {2 + 2 = 4} \right)$. Thus it is not in order of $\left( {4n + 2} \right)$, therefore it is not an aromatic compound.

Hence the correct option is C.

Note:
It must be noted that each pi bond constitutes two electrons and a negative charge accounts for two electrons where a positive charge does not account for any electron. This is because a negative charge is developed when atoms accept electrons and a positive charge is developed when atoms lose electrons. Also for aromatic compounds, the compound must be planar.