# How do you determine acidity of aromatic compounds?

Jun 22, 2017

The $p {K}_{a}$ of $\text{benzoic acid}$, ${C}_{6} {H}_{5} C {O}_{2} H$, is known and widely reported, $p {K}_{a} = 4.202$. This means that is a stronger acid than that of $\text{acetic acid}$, $p {K}_{a} = 4.76$, and this is probably an entropy effect in that $\text{benzoate}$ anion is less charge dense than $\text{acetate}$.
On the other hand, the $p {K}_{a}$ of $\text{phenol}$, ${C}_{6} {H}_{5} O H$ is $9.95$.