Question

Why does the ${\mathrm{NO}}_2$ group show its effect only in ortho?

Answer 1

Ortho positions :

In organic chemistry, an ortho position is one in which two identical functional groups are bound to positions 1 and 2 of a benzene ring.

Resonating structures in nitrobenzene:

1. The presence of $N{O}_2$ groups at the ortho and para positions pushes electron density away from the benzene ring, facilitating the nucleophile's interaction very easily.
2. Also, the negative charge is not stabilized by the presence of the nitro group at the meta position.
3. The existence of the $N{O}_2$ group at the meta position has no impact on reactivity.