Phenol + dil. HNO3 (aq) ->
at room temperature.
We all know that the substituent -NO2 could be substituted
on the 2nd, 4th, or 6th position.
Usually, we write the mole ratio of 2-nitro and 4-nitrophenol as
1:1.
But since 2-nitrophenol is the same as "6-nitrophenol",
shouldn't the mole ratio of 2-nitrophenol:4-nitrophenol be 2:1?
>>> But since 2-nitrophenol is the same as
"6-nitrophenol", shouldn't the mole ratio of
2-nitrophenol:4-nitrophenol be 2:1? <<<
Your train of thought is correct, but... (read on
below)
>>> Usually, we write the mole ratio of 2-nitro and
4-nitrophenol as 1:1. <<<
This is not correct. We (ie. you, in the exam) only write it
that way to show that a MIXTURE of ortho(or 2)-nitrophenol and
para(or 4)-nitrophenol is obtained. It is NOT meant to be a
stoichiometric value.
There is another factor to consider - steric hinderance would
result in the para position to be favoured by the incoming
electrophile, rather than the ortho positions.
In practice, the exact ratio of ortho and para isomers is
certainly not 1:1 (at 'A' levels, you don't need to know the exact
ratio, you only need to say a mixture of both isomers is
obtained).