MCQ Detailed View

The solubility of organic compounds in water depends largely on their ability to form hydrogen bonds with water molecules. Phenols are generally soluble in water because the –OH group can form intermolecular hydrogen bonds with water. However, the position of substituents on the benzene ring strongly influences solubility.

In o-nitrophenol, the nitro group (–NO₂) is located adjacent to the –OH group. This allows the formation of intramolecular hydrogen bonding between the hydrogen atom of the –OH group and one of the oxygen atoms of the nitro group. Because of this internal hydrogen bonding, the hydroxyl hydrogen is not free to interact with water molecules. As a result, the ability of o-nitrophenol to form hydrogen bonds with water is reduced, leading to very low solubility in water.

On the other hand, p-nitrophenol does not have this possibility for intramolecular hydrogen bonding. Instead, it forms intermolecular hydrogen bonds with water molecules, making p-nitrophenol significantly more soluble than o-nitrophenol.

Looking at the options:

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  Inductive effect does play a role in acidity and reactivity but does not explain solubility differences here.

  
  


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  Resonance effect stabilizes charge distribution but is not the primary reason for insolubility in this case.

  
  


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  Intramolecular hydrogen bonding is the correct explanation, because it prevents the –OH group from interacting with water molecules.

  
  


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  Isomeric effect is too general and does not specifically explain the observed solubility behavior.

  
  

Thus, the insolubility of o-nitrophenol in water is best explained by intramolecular hydrogen bonding, which locks the –OH group within the molecule, reducing its capacity to form hydrogen bonds with water.