Q.The intramolecular hydrogen bonding is present in :

o-Nitrophenol shows intramolecular hydrogen bonding because its -OH and -NO2 groups are close enough (on adjacent ring carbons) to bond with each other within the same molecule.

In ortho-nitrophenol, the -OH group and the -NO2 group are positioned on carbon atoms next to each other on the benzene ring. This proximity allows the hydrogen of the -OH group to hydrogen-bond intramolecularly with one of the oxygen atoms of the neighbouring -NO2 group, forming a stable six-membered chelate ring within the single molecule.

In meta- and para-nitrophenol, the -OH and -NO2 groups are too far apart geometrically for such a ring to form within one molecule; instead, molecules hydrogen-bond to each other (intermolecular hydrogen bonding), causing association between molecules. Plain phenol has no second polar group to hydrogen-bond with at all.

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