Question

Arrange the following in decreasing order of their acidic strengths :

• A. $A>B>C>D$
• B. $D>C>B>A$
• C. $A>D>C>B$
• D. $D>B>C>A$

Answer 1

The correct option is C $A>D>C>B$

After the loss of proton, conjugate bases formed are :


Since, on losing $H^{+}$, structure A and D become neutral, so they are more stable than B and C
Between B and C :
Negative charge on more electronegative atom (oxygen) is more stable, as in structure C than less electronegative atom (nitrogen) as in structure B.
So, C is more stable than B.
Between A and D :
More the electronegativity, more is the stability of conjugate base.
Since electronegativity of oxygen is more than that of nitrogen
So, A is more stable than D
Overall order of stability of conjugate base :
$A>D>C>B$

$\text{Stability of conjugate base}\propto \text{Acidic strength}$

Acidic strength order :
$A>D>C>B$