Question

Explain how does the OH group attached to a carbon of benzene ring activate it towards electrophilic substitution?

Answer 1

Hint: Electrophilic substitution reaction involves the displacement of the functional group by an electrophile (generally a hydrogen atom). Electrophiles are those that are attracted to electrons.

Complete step by step answer:
- Let’s discuss about how the OH group attached to a carbon of benzene ring activate it towards electrophilic substitution:
- It is found that if any electrophile has to react with a benzene ring, then the benzene ring should have more electron density inside the ring. So that the electrophile can attack on it.
- In all these cases, the negative charge of Ortho and para position is slightly more conserved. So, any electrophile that will react on it will give Ortho and para products.

- If we will see the resonating structure of phenol, in that due to the lone pair of oxygen, its resonating structures will be formed like:

- In case of phenol rapid reaction takes place and gives ortho and para products. When phenol is reacted in presence of bromine, then bromine will attack on all the three positions, this happens because their rings become more activated. We can see the reaction as:

Note: - We should not get confused in between electrophilic substitution reaction and electrophilic addition reaction. Electrophilic substitution reaction involves the displacement of a functional group by an electrophile. Whereas, in electrophilic addition reaction species add into a molecule, but don't replace a leaving group.