Define Activating And Deactivating Groups And List 2 Examples Of Each
The correct answer and explanation is :
Activating and Deactivating Groups:
In organic chemistry, activating and deactivating groups refer to substituents attached to a benzene ring that affect the reactivity of the ring towards electrophilic aromatic substitution (EAS) reactions. The nature of these groups determines how easily the ring will undergo substitution and which positions on the ring are most likely to undergo reaction.
- Activating Groups: Activating groups are electron-donating groups (EDGs) that increase the electron density on the benzene ring. This makes the ring more reactive toward electrophiles, as it stabilizes the intermediate carbocation in EAS reactions. These groups typically donate electrons through resonance or inductively, increasing the electron density at the ortho and para positions relative to the substituent. Examples of Activating Groups:
- –OH (Hydroxyl group): The oxygen atom in the hydroxyl group has lone pairs of electrons that it can donate to the benzene ring via resonance, making the ring more reactive to electrophilic attack at the ortho and para positions.
- –NH₂ (Amino group): The nitrogen in the amino group also has lone pairs that it donates to the benzene ring, significantly increasing the electron density, especially at the ortho and para positions.
- Deactivating Groups: Deactivating groups are electron-withdrawing groups (EWGs) that decrease the electron density on the benzene ring. These groups make the ring less reactive toward electrophiles, as they destabilize the intermediate carbocation in EAS reactions. Deactivating groups typically withdraw electrons through resonance or inductively, which decreases the electron density at the ortho and para positions, making them less reactive. Examples of Deactivating Groups:
- –NO₂ (Nitro group): The nitro group is a strong electron-withdrawing group through both resonance and induction. It withdraws electron density from the benzene ring, making the ring less reactive and decreasing the likelihood of substitution at the ortho and para positions.
- –COOH (Carboxyl group): The carboxyl group also withdraws electrons from the benzene ring through resonance and inductive effects, making the ring less reactive toward electrophilic substitution reactions.
In summary, activating groups increase the electron density on the benzene ring, making it more reactive to electrophilic aromatic substitution, while deactivating groups withdraw electrons, decreasing the reactivity of the ring.