Question: 57. Intramolecular hydrogen bonding is present in :
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Answer: Option (1)
Explanation:
Intramolecular hydrogen bonding occurs when a hydrogen bond is formed within the same molecule between a hydrogen atom bonded to an electronegative atom and another electronegative atom present in the same molecule.
In option (1), the compound is o-nitrophenol.
Here, the hydroxyl group \mathrm{-OH} and
the nitro group \mathrm{-NO_2} are present at adjacent (ortho) positions on the benzene ring.
This close proximity allows the hydrogen atom of the hydroxyl group to form a hydrogen bond with the oxygen atom of the nitro group within the same molecule, resulting in intramolecular hydrogen bonding.
In option (2), p-nitrophenol has the \mathrm{-OH} and \mathrm{-NO_2} groups at para positions,
which are too far apart to form intramolecular hydrogen bonding.
In option (3), m-nitrophenol has the groups at meta positions,
which also do not allow intramolecular hydrogen bonding.
In option (4), HF forms intermolecular hydrogen bonding between different molecules,
not intramolecular hydrogen bonding.
Therefore, intramolecular hydrogen bonding is present only in option (1).