- Nitro group at para position has dominant -M effect (mesomeric effect) but has -I effect (inductive effect) also while nitro group at meta position on benzene ring has only -I effect.
- When both acids donate their proton from -COOH group then p-nitrobenzoate is more stabilized due to -M effect of nitro group than m-nitribenzoate because -M group more deactivates the ring / decreases charge than -I group.
- Thus, p-nitrobenzoic acid is more acidic than m-nitrobenzoic acid.