Question

How do you count pi electrons in aromatic compounds?

Answer 1

Hint Each bond either sigma or pi-bond, will contain two electrons each compulsorily. The aromatic compounds can have either a double bond or a triple bond with a ring structure.

Complete step by step solution:
Let us learn about the basics needed to answer the given question,
There are two types of bonds i.e. either sigma bond $\left( \sigma -bond \right)$ or a pi bond $\left( \pi -bond \right)$ . The compounds having all the sigma bonds are known as saturated compounds whereas, the ones including pi bonds will be called as unsaturated compounds.
For alkene- There is a sigma bond and a pi bond present when it forms a double bond. Thus, the number of electrons in the pi bonds will be two times the number of bonds present in the molecule.
For alkyne- Similarly, there is a sigma bond and two pi bonds present in the molecule forming a triple bond. Thus, the number of electrons will be two times the number of bonds present in the molecule.
Thus, we can say that in general we need to identify the pi-bonds in the molecule and then multiply by 2 to the number of pi-bonds present.

Note: Do note that the pi electrons that are in the ring count towards the aromaticity. Thus, if the lone pairs are present in the aromatic compounds do not get confused. Also, Huckle’s rule is sometimes used to verify the aromaticity of a compound by counting the number of electrons in it. The formula for Huckle’s rule is 4n+2 where, n is the whole number from 0 to 6.