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Question: The correct order of acidity of the alcohols is: (A)- \({{1}^{\circ }}>{{11}^{\circ }}>{{111}^{\ci...

The correct order of acidity of the alcohols is:
(A)- 1∘>11∘>111∘{{1}^{\circ }}>{{11}^{\circ }}>{{111}^{\circ }}
(B)- 111∘>11∘>1∘{{111}^{\circ }}>{{11}^{\circ }}>{{1}^{\circ }}
(C)- 1∘>111∘>11∘{{1}^{\circ }}>{{111}^{\circ }}>{{11}^{\circ }}
(D)- 11∘>111∘>1∘{{11}^{\circ }}>{{111}^{\circ }}>{{1}^{\circ }}

Explanation

Solution

The acidity of the alcohol is dependent on the stability of its conjugate base. The stability of these conjugate bases is affected by the inductive effect from the electron-donating group.

Complete step by step answer:
Acidity is the tendency of a molecule to lose its proton. In case of simple alcohols, the acidic nature is found due to the presence of the electronegative oxygen atom in the O-H bond which attracts the bond pair electrons towards itself. Thus, making the loss of H+{{\text{H}}^{\text{+}}} ions easier.
So, the alcohols on losing a proton form an alkoxide ion (R−O−)(R-{{O}^{-}}), which is a conjugate base.
R−O−H⇄R−O−+H+R-O-H\rightleftarrows R-{{O}^{-}}+{{H}^{+}}
More the stability of the alkoxide ion formed, the reaction shifts to the right side. Thereby, increasing the acidity of the alcohol. Also, the stable alkoxide is a weaker base.

In the primary, secondary and tertiary alcohols having an increase in the number of alkyl groups attached to the central carbon atom. That is, the primary alcohol having a single alkyl group, secondary alcohol having two alkyl groups and the tertiary alcohol having three alkyl groups attached to the central carbon adjacent to the O-H bond.
These alkyl groups are electron-donating groups and show positive inductive effect. Then, the stability of the alkoxide is further affected by these alkyl groups.

As the number of alkyl groups attached to the central carbon atom increases, the inductive effect increases, which further increases the electron-density on the adjacent oxygen atom. This makes the alkoxide unstable, shifting the equilibrium to the left side. Thus, decreasing the acidity of the alcohol.

Therefore, the order of acidity of the alcohols is option (A)- 1∘>11∘>111∘{{1}^{\circ }}>{{11}^{\circ }}>{{111}^{\circ }}.

Note: The alcohols are weak acids. The acidity of the tertiary alcohol is also affected by the number of alkyl groups attached which makes it bulky and hinders the loss of proton.
Also, in the gas phase, the order of acidity gets reversed, making the tertiary alcohol most acidic.