Which of the following is the major product formed when phenol is treated with dilute nitric acid at 293 K?

When phenol is treated with dilute nitric acid at 293 K, the major products formed are ortho-nitrophenol and para-nitrophenol. However, ortho-nitrophenol predominates due to the stability provided by intramolecular hydrogen bonding.

Analysis of the Reaction

1. Electrophilic Aromatic Substitution: The reaction involves the electrophilic substitution of a nitro group (−NO2−NO2) onto the aromatic ring of phenol. The hydroxyl group (−OH−OH) on phenol is an activating group that directs the incoming nitro group to the ortho and para positions.
2. Product Formation:
   • Ortho-Nitrophenol: Formed when the nitro group is added to the carbon adjacent to the hydroxyl group.
   • Para-Nitrophenol: Formed when the nitro group is added to the carbon opposite to the hydroxyl group.
3. Major Product: While both ortho and para products are formed, ortho-nitrophenol is favored because:
   • It can form an intramolecular hydrogen bond between the hydroxyl and nitro groups, which stabilizes the ortho product.
   • Steric hindrance is less significant at lower temperatures (293 K), allowing for more ortho product formation.

The correct answer is that ortho-nitrophenol predominates, but since it isn't listed as an option, we can conclude that the major products are a mixture of ortho- and para-nitrophenols, with ortho-nitrophenol being more prevalent.