Sort the following groups as ortho para and meta directing:
Group
-OCOR
Effect in EAS
[Select]
-NHCOCH
ortho para (electron donatir
-COOR
[Select]
-NH2
ortho para (electron donatir
[Select]
ortho para (electron donating, strong activating)
meta (electron withdrawing, strong deactivating)
ortho para (electron donating, moderate activating)
meta (electron withdrawing, moderate deactivating
The Correct Answer and Explanation is :
To classify the given groups as ortho/para or meta directing, let’s analyze their effects in electrophilic aromatic substitution (EAS):
- -OCOR (Acyl group): This group is meta-directing and electron-withdrawing. The carbonyl group (C=O) pulls electron density away from the ring, making it less reactive towards electrophiles. As a result, it directs new substituents to the meta position in EAS reactions. This group is a strong deactivator.
- -NHCOCH (Amide group): This group is ortho/para-directing and an electron donor. The nitrogen in the amide group donates electron density to the aromatic ring via resonance, activating the ring and directing substituents to the ortho and para positions. However, the carbonyl group also withdraws some electron density, making the activation less strong compared to groups like -NH2.
- -COOR (Ester group): This group is meta-directing and electron-withdrawing. Like the acyl group, the ester group has a carbonyl functionality that pulls electron density away from the ring, making it less reactive. As a result, it directs incoming electrophiles to the meta position, and it acts as a moderate deactivator.
- -NH2 (Amino group): The amino group is ortho/para-directing and a strong electron donor. The lone pair of electrons on the nitrogen atom can donate electron density into the aromatic ring, significantly increasing the ring’s reactivity towards electrophiles. Thus, it activates the ring and directs substitution to the ortho and para positions.
Summary Classification:
- -OCOR: Meta-directing, electron-withdrawing, strong deactivator.
- -NHCOCH: Ortho/para-directing, electron-donating, moderate activator.
- -COOR: Meta-directing, electron-withdrawing, moderate deactivator.
- -NH2: Ortho/para-directing, electron-donating, strong activator.