91Ó°ÊÓ

In electrophilic aromatic substitution reaction, each substituent plays a very important role, either in increasing or decreasing the electron density in the benzene ring. This will affect the course of the substitution reaction. Donation of electrons cloud or density to the benzene ring by the substituents make the ring more electron rich, therefore more likely to interacts with an electrophile. For example a methoxy substituent increases the rate of electrophilic substitution reaction about ten thousand folds.

The greater the electron-withdrawing ability of the para substituent, the greater will be the K_eq for the hydrate formation. The decreasing order of electron withdrawing group is shown below:

NO₂> Cl > CH₃> OCH₃

The greater the electron-withdrawing ability of the para substituent, the greater will be the K_eq for the hydrate formation. Here, nitro group is most electron-withdrawing in nature, therefore they have the greater value of K_eq for the hydrate formation.

Order of decreasing K_eq