Hydrogen Bonding: Why p-Nitrophenol Is Less Volatile Than o-Nitrophenol

Same formula (C6H5NO3), same functional groups, yet o-nitrophenol melts at about 45 °C and p-nitrophenol at about 114 °C. Why is the para isomer so much harder to vaporize?

How intramolecular and intermolecular hydrogen bonding decide melting point, volatility and solubility, how the chemistry lab separates the two isomers by steam distillation, and the traps NEET likes to test.

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In this video

• 0:00The puzzle: two nitrophenols, same formula
• 1:03What is a hydrogen bond? Intermolecular vs intramolecular
• 2:23Why hydrogen bonding controls volatility
• 3:20o-Nitrophenol: the hydrogen bond closes a six-membered ring
• 4:37p-Nitrophenol: groups too far apart, so a chain forms
• 5:35Side by side: one cause, four consequences
• 6:31Steam distillation set-up and why it works
• 8:44Going further: resonance-assisted H-bond, IR/NMR dilution test, the acidity flip
• 11:02Three quick checks
• 11:39Wrap-up