Question

The correct order of increasing acidic strength is

• A. phenol $<$ ethanol $<$chloroacetic acid $<$ acetic acid
• B. ethanol $<$ phenol $<$chloroacetic acid $<$ acetic acid
• C. ethanol $<$ phenol $<$ acetic acid $<$ chloroacetic acid
• D. chloroacetic acid $<$ acetic acid $<$phenol $<$ ethanol

Answer 1

The correct option is C

ethanol $<$ phenol $<$ acetic acid $<$ chloroacetic acid

The explanation for the correct option:

Option (C): ethanol $<$ phenol $<$ acetic acid $<$ chloroacetic acid

1. The tendency of an acid, to dissociate into a proton and an anion is known as acid strength.
2. A more stable conjugate base makes an acid more acidic than a less stable conjugate base does.
3. After an acid donates a proton during a chemical process, what is left over is a conjugate base. Consequently, a conjugate base is a species created when a proton is taken out of acid.
4. Conjugate base of ethanol is an ethoxide ion, and the conjugate base of phenol is a phenoxide ion, formed by deprotonation of the $\mathrm{OH}$ group. the conjugate base of Acetic acid is an acetate ion and the conjugate base of chloroacetic acid is a carboxylate ion.
5. Due to the delocalization of the negative charge, phenoxide ions are more stable than ethoxide ions. The highly electronegative oxygen ion in phenoxide has a large electron density and is stabilized by resonance, but the ethoxide ion is unstable because resonance does not occur and the negative charge is not delocalized. Hence, phenol is more acidic than ethanol.
6. Acetate can be stabilized more successfully by resonance than phenoxide. This is due to the fact that in the latter, in some canonical configurations, the negative charge is applied to less electronegative Carbon. On the other hand, acetate has two identical resonating structures. Because acetate is more stable than phenoxide, acetic acid is more acidic than phenol.
7. The chlorine group at chloroacetic acid is an electron-withdrawing group. By dispersing the negative charge through the inductive effect and stabilizing the acetate anion, it makes acetic acid more acidic. Hence, chloroacetic acid is more stable than acetic acid.
8. Hence, it is the correct option.

Therefore, the correct order of increasing acidic strength is Ethanol $<$ phenol $<$ acetic acid $<$ chloroacetic acid