Which of the following is the strongest acid ?

Options

A. Phenol
B. `o-`Methoxyphenol
C. `m-`Methoxyphenol
D. `p-`Methoxyphenol

Answer

C

Explanation

`-I_(effect)(o gt m gt p),+R_(effect)(o~~p, not m),+R_(effect) gt -I_(effect)`
Group like `OCH_(3)` with `a+R` effect weaken the phenol's acidic strength when in the `o-` position or `p-`position but strengthen its acidic strength when in the `m-`position. In the latter case, only the `-I_(effect)` can opereate. Thus, the decreasing order of acidity is

Since the `-I_(effect) of -OCH_(3)` group is more than that of `NH_(2)` group, `m-`methoxyphenol is a stronger acid than `m-`aminophenol.