Question

The substituent which is predominantly ortho-para directing but deactivating in aromatic electrophilic substitution reaction is:
A.) $ - N{O_2}$
B.) $ - OC{H_3}$
C.) $ - C{H_3}$
D.) $ - Cl$

Answer 1

Hint: The ortho- para directing groups are those in which the substituents are placed at ortho and para position and generally electron donating groups are ortho para directing. Also, the deactivating groups are groups which withdraw the electrons from the ring.

Complete answer:
As we know that the ortho-para directing groups are those groups which favors the attack of electrophile at ortho and para position in the aromatic electrophilic substitution reaction and the meta directing groups favors the attack of electrophile at meta position in the aromatic electrophilic substitution reaction.
Also, the deactivating groups are those groups which deactivate the ring by the inductive effect in the presence of an electronegative group. This is because the electronegative group attracts the electrons away from the ring and makes the ring less stable.
In case of Chlorine ($Cl$) , due to its electronegative nature, it shows negative inductive effect ($ - I$) and withdraws the electrons away from the ring thus it makes the ring deactivating towards aromatic electrophilic substitution .
Also, the Chlorine group has a lone pair on it. Chlorine donate its lone pair to the aromatic ring and hence increase the electron density at ortho and para position. Therefore, chlorine is a deactivating group. The resonating structures of chlorobenzene can be shown as:

Hence, option (D) is the correct option.

Note:
Always remember that chlorine is an electronegative element due to which it attracts the electrons from the ring and deactivates the ring to which it is attached and also it has a lone pair and by donating that lone pair it makes the ring predominantly ortho para directing.