Why para-nitro phenol has high B.P. then ortho-nitro phenol?

O-nitrophenol shows intramolecular Hydrogen bonding where as p-nitrophenol shows intermolecular Hydrogen bonding. This intermolecular H-bonding causes association of molecules in p-nitrophenol while there is no such association in o-nitrophenol. Therefore the boiling point of p-nitophenol is higher than o-nitrophenol.

Intramolecular H- bonding in O-nitrophenol