Question

The correct order of acid strength of the following substituted phenols in water at ${28}^{o}C$ is:

• A. p-nitrophenol< p-fluorophenol< p-chlorophenol
• B. p-chlorophenol<p-fluorophenol<p-nitrophenol
• C. p-fluorophenol< p-chlorophenol< p-nitrophenol
• D. p-fluorophenol< p-nitrophenol< p-chlorophenol

Answer 1

The correct option is C p-fluorophenol< p-chlorophenol< p-nitrophenol

The order of electron withdrawing tendency from benzene ring is:
$-F<-Cl<-{NO}_2$

p-chlorophenol is more acidic because fluorine and carbon have identical p orbitals and because of that there overlapping is perfect .Hence it cancels +R effect and -I effect. Thus making p-fluorophenol is less acidic.

$\therefore$ Correct order of acidic strength of substituted phenols will be as shown in option C.