What is the Difference Between Ortho Para and Meta Substitution?

The difference between ortho, para, and meta substitution lies in the position of the substituents on a benzene ring. Here's a breakdown of each type of substitution:

1. Ortho substitution: In this case, the substituents are located at the 1,2 positions on the benzene ring, meaning they are bonded to two adjacent carbon atoms.
2. Para substitution: In this substitution, the substituents are located at the 1,4 positions on the benzene ring, meaning they are bonded to two carbon atoms separated by two carbon atoms in the ring.
3. Meta substitution: In this substitution, the substituents are located at the 1,3 positions on the benzene ring, meaning they are bonded to two carbon atoms separated by one carbon atom in the ring.

These positions are named based on their relationship to each other on the benzene ring. Ortho refers to the two adjacent positions, para refers to the opposite position (separated by two carbon atoms), and meta refers to the position in between ortho and para (separated by one carbon atom).

Comparative Table: Ortho Para vs Meta Substitution

The difference between ortho, para, and meta substitution lies in the positions on a benzene ring where a substituent can be located. In electrophilic aromatic substitution reactions, certain substituents direct the electrophile to specific positions, leading to the formation of ortho, para, or meta products.

In general, ortho and para products are favored over meta products due to the steric strain between the closer-located ortho substituent and the larger the groups, the higher the strain, therefore the higher the regioselectivity. However, electron-withdrawing groups slow down substitutions at all positions but favor the meta substitution because it is less unfavorable than the ortho and para substitutions.