Two flasks each contain phenol. Flask P receives bromine water at room temperature; flask Q receives bromine dissolved in CS2 at low temperature. What forms in each flask?
A
P: 3-bromophenol; Q: 3,5-dibromophenol
B
P: bromobenzene, as the OH group is replaced; Q: no reaction
C
P: a white precipitate of 2,4,6-tribromophenol; Q: a mixture of ortho- and para-bromophenols
D
P: a mixture of ortho- and para-bromophenols; Q: 2,4,6-tribromophenol
Show the answer
The answer is C.
The –OH group strongly activates the ring towards ortho and para substitution. In water bromination goes all the way to a white precipitate of 2,4,6-tribromophenol, while in a less polar solvent such as CS2 at low temperature monobromophenols (ortho and para) are formed.
A.
The –OH group directs substitution to the ortho and para positions, not meta.
B.
Bromine substitutes ring hydrogens; it does not replace the –OH group, and phenol does react in CS2.
D.
This reverses the two conditions: the polar solvent water gives trisubstitution, the non-polar CS2 gives monobromophenols.
NCERT: Class 12 Chemistry, Chapter 7
Practise Phenols: acidic nature and electrophilic substitution
Practice at the level you choose, with the answer after every question; timed tests with the answers when you submit. Every question is verified against NCERT first.