Question

How Do You Know Which Group Is Activating And Deactivating?

Answer 1

• Activating group:

1. Atoms or groups that make the benzene molecule more reactive by increasing the ring's electron density are called activating groups.
2. Activating groups serve as ortho‐para directors when they are attached to a benzene ring, meaning that they direct an incoming electrophile to the ortho or para positions.
3. Activating groups increases the rate of reaction relative to $\mathrm{H}$.

Example: Common activating groups include : $\mathrm{Alkyl},{\mathrm{NH}}_2,{\mathrm{NR}}_2,\mathrm{OH},{\mathrm{OCH}}_3,\mathrm{SR}\mathrm{etc}.$

• Deactivating group:

1. An atom or group that makes the benzene molecule less reactive by removing electron density from the ring acts as a deactivating group.
2. Deactivating groups direct incoming electrophiles to the meta position. Activating groups decreases the rate of reaction relative to $\mathrm{H}$.

Example: Common deactivating groups : ${\mathrm{NO}}_2,{\mathrm{CF}}_3,\mathrm{CN},\mathrm{halogens},\mathrm{COOH},{\mathrm{SO}}_3\mathrm{H}\mathrm{etc}.$

1. We must be aware that a group is activating that accelerates the process of electrophilic aromatic substitution in comparison to hydrogen. The rate of nitration is accelerated when ${\mathrm{CH}}_3$ is used to substitute a hydrogen atom on benzene.
2. An electrophilic aromatic substitution process is slowed down with a deactivating group than it does with hydrogen. The rate of nitration is drastically decreased when the trifluoromethyl group, ${\mathrm{CF}}_3$, is substituted for a hydrogen on benzene.
3. As a result, the stability of the activating group increases as the reactivity of the electrophilic substitution process increases. The stability of a deactivating group decreases, which reduces the group's reactivity.