JEE Main · 2024 · 01 Feb 2024 · Shift 2 · Chemical Bonding and Molecular Structure

Intramolecular hydrogen bonding requires a donor and acceptor within the same molecule, positioned to close a ring. $H_{2}O$, $N{H}_3$, and $C_2{H}_{5}OH$ only hydrogen-bond between separate molecules of the same compound — intermolecular bonding. In o-nitrophenol, the $-OH$ hydrogen sits close to an oxygen of the adjacent $-N{O}_2$ group; the two form a six-membered hydrogen-bonded ring within the single molecule. This intramolecular bonding is why o-nitrophenol is less water-soluble and has a markedly lower boiling point than its para isomer, which instead engages in intermolecular hydrogen bonding.