Question

Arrange in order of increasing acidic strength.

• A. X>Z>Y
• B. Z< x >Y
• C. X>Y>Z
• D. Z>X>Y

Answer 1

Answer: (A)

$p{K}_a$ value of carboxylic group is less than $p{K}_a$ of $N\stackrel{+}{H_3}$ in amino acid and $-N\stackrel{+}{H_3}(Z)$ will have comparatively less $p{K}_a$ than $-N\stackrel{+}{H_3}(Y)$ due to -I effect of carboxylic group. We know that acidic strength in inversely proportional to $p{K}_a$. Hence, correct order of acidic strength is
$-C{O}_{2}H(X)>-N\stackrel{+}{H_3}(Z)>-N\stackrel{+}{H_3}(Y)$