Question

Phenol reacts with bromine in carbon disulphide at low temperature to give:
A) M-bromophenol
B) O- and p- bromophenol
C) P- bromophenol
D) 2,4,6- tribromophenol

Answer 1

Hint:
To answer this question, you must recall the reactions of phenol and its substituents. Phenol reacts with bromine in presence of a non- polar solvent like carbon disulphide and undergoes monohalogenation.

Complete step by step solution:
We know that phenol is an aromatic alcohol having a hydroxyl group attached on a benzene ring. Since oxygen is an electron withdrawing group and withdraws electron density from the benzene ring inductively. But the lone pair on the oxygen atom participates in delocalization of electrons along with the aromatic benzene ring acting as an electron donating group metamerically.
Due to continuous delocalization of electrons through resonance, the electron density will be different at different positions in all the resonance structures. However, the electron density is maximum at the ortho and para positions while it is comparatively less at the Meta position. Hence, in phenols, the ortho and para positions are susceptible to electrophilic attack as the incoming electrophile will attach to that carbon having high electron density.
The reaction of bromine with phenol in presence of carbon disulphide is an example of an electrophilic substitution reaction. The attacking electrophile is positively charged bromine cation. Since, we know that the ortho and para positions are more susceptible to electrophilic attack, thus, the bromine will attach to either the ortho position or para position forming O- and p- bromophenol.

Thus, the correct answer is B.

Note:
When bromine water is reacted with phenol we obtain 2,4,6- tribromophenol as the product. But in non- polar solvents, the ionization of phenol is highly suppressed. Thus, the hydroxyl group donates electrons to the ring to a lesser extent activating the ring slightly and thus, mono substitution occurs.