Question

Why ortho-nitrophenol is steam volatile while para-nitrophenol is not?

Answer 1

In o-nitrophenol, oxygen in the NO₂ group forms an intramolecular hydrogen bond with hydrogen in the hydroxide group. While in the p-nitrophenol, oxygen in the NO₂ group of one molecule forms an intermolecular hydrogen bond with hydrogen in the hydroxide group of another molecule.

Since intramolecular hydrogen bonds are weaker than intermolecular hydrogen bonds, o-nitrophenol is less steam volatile than p-nitrophenol.