o-nitro phenol has lower boiling point than p–nitro phenol. Explain?
Answers
In p-nitrophenol, molecular association takes place due to extensive hydrogen bonding between the molecules (intermolecular hydrogen bonding). Therefore, it has higher melting and boiling points. In o-nitrophenol, since the OH and NO2 are in close proximity to each other, intramolecular hydrogen bonding takes place.
If a substance has hydrogen bonding then its boiling point is more than the normally expected according to molecular weight of the compound. In the given case, both o-nitro phenol and p-nitro phenol are isomers.
This is due to the difference in the type of hydrogen bonding present. The o-nitro phenol has intramolecular hydrogen bonding and p-nitro phenol has intermolecular hydrogen bonding.
"Intermolecular hydrogen bonding" is strong and can raise the boiling point whereas "intramolecular hydrogen bond" is not capable of doing that.
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