The difference in the reaction of phenol with bromine in chloroform and bromine in water medium is due to :

Solution

Chemistry ma’am · 3 steps

Same phenol, same bromine: the solvent decides whether phenol stays neutral or ionises to phenoxide.

1. In chloroform. CHCl₃ is a low-polarity solvent, so phenol does not ionise and Br₂ is not strongly polarised. The -OH group activates the ring only moderately, giving mainly monobromophenols (o- and p-bromophenol) at low temperature.
2. In water. Water is highly polar. It lets phenol partly ionise to the phenoxide ion, which activates the ring much more strongly than -OH, and it also polarises Br₂ into a better electrophile.

   C₆H₅OH + 3Br₂ →(H₂O) 2,4,6-Br₃C₆H₂OH v + 3HBr

3. So. All three ortho and para positions get substituted, and a white precipitate of 2,4,6-tribromophenol forms. The only thing that changed between the two reactions is the solvent, so the difference is due to the polarity of the solvent, option (b).

The idea to keep. Polar solvent means more phenoxide and a more polarised Br₂, so you get tribromination. Non-polar solvent at low temperature gives monobromination.

Answer from the NTA final answer key. Solution by PrepWiser.