Atoms or groups that make the benzene molecule more reactive by increasing the ring's electron density are called activating groups.
An atom or group that makes the benzene molecule less reactive by removing electron density from the ring acts as a deactivating group. Deactivating groups direct incoming electrophiles to the meta position. Deactivating groups decreases the rate of reaction relative to H. If the atom of the group attached to benzene ring has pi bond then that group act as deactivating group.
Hence, −CN,−COCH3 are deactivating groups.
