Q17-59E - Organic Chemistry (Mcmurry)

Question

Rank the following substituted phenol in the increasing order of acidity, and explain your answer:

Step-by-Step Solution

Answer

The answer is 

Step 1: Acidity in phenols

The acidity of alcohols can be defined as the tendency of alcohols to donate the protons and forms a stable oxide anion. The acidity of alcohols depends on the stability of the oxide anion formed.

Step 2: Explanation

The increasing order of acidity is shown below.

Electron-withdrawing groups on phenol can stabilise the anions formed after losing the protons(that is phenoxide ion) and hence become more acidic. The electron-donating groups, in turn, decrease acidity.

-CN group can stabilise the phenoxide ion by mesomeric effect.

-F is an electronegative atom.

$-{\mathrm{OCH}}_3$is an electron donating group that will decrease the acidity of the phenol.