MediumChemistryHigh School (11–12)Chemical Bonding › Molecular Orbitals and Hydrogen BondsConceptual
A mixture of ortho-nitrophenol and para-nitrophenol is steam distilled.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A mixture of ortho-nitrophenol and para-nitrophenol is steam distilled. One of them comes over with the steam and the other stays behind. Which one distils, and why?
Need a reminder? The key ideaShow
A hydrogen bond is the attraction between a hydrogen atom joined to fluorine, oxygen or nitrogen and a lone pair on another such atom. Intermolecular hydrogen bonds join molecules and raise boiling points; intramolecular ones form within one molecule. Water boils at , far above , and .
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Ortho. The group and the nitro group are next to each other, so a hydrogen bond forms inside the molecule. The molecules are not held to each other.
Step 2. Para. The two groups are far apart, so hydrogen bonds join one molecule to the next.
Step 3. Volatility. Molecules held only weakly to their neighbours escape more easily.
Answer: ortho-nitrophenol distils with the steam; its hydrogen bond is intramolecular, while para-nitrophenol is held by intermolecular hydrogen bonds.
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