Question

Arrange the following compounds in increasing order of their acid strength:

Propan-1-ol, 2,4,6-trinitrophenol,

3-nitrophenol, 3,5-dinitrophenol, phenol, 4-methylphenol

Answer 1

Increasing order of acidic strength

We know that, phenol is a stronger acid than alcohol. Also, order of acidic strength of alcohols and phenols is given by considering the fact that $+I$ groups like methyl $(-C{H}_3)$ group being electron releasing in nature, decreases the acidic strength of phenol while $-I$ groups like nitro $(-N{O}_2)$ group being electron withdrawing in nature, increases the acidic strength of phenol.

Hence, the increasing order of acidic strength is :

$Propan-1-ol<4-methylphenol<phenol<3-nitrophenol<3,5-dinitrophenol<2,4,6-trinitrophenol$