Which among following amines has lowest $\mathrm{pK}_{\mathrm{b}}$ values?

Which among following amines has lowest $\mathrm{pK}_{\mathrm{b}}$ values?
  1. $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{NH}_2$
  2. $\left(\mathrm{CH}_3 \mathrm{CH}_2\right)_2 \mathrm{NH}$
  3. $\left(\mathrm{CH}_3 \mathrm{CH}_2\right)_3 \mathrm{~N}$
  4. $\mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2$

Solution

$\begin{aligned}\left(\mathrm{CH}_3 \mathrm{CH}_2\right)_2 \mathrm{NH} & \Rightarrow 2^{\circ} \text { amine } \\ & \Rightarrow \text { Most basic } \\ & \Rightarrow \text { Least } \mathrm{pK}_{\mathrm{b}}\end{aligned}$

Asked in: MHT CET 2021 (21 Sep Shift 2)

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