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STD 12 - 9. Amines — NEET STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceNEETSTD 12 - 9. Amines4 Marks
MCQ
Considering the basic strength of amines in aqueous solution, which one has the smallest $pK_b$ value ?
  • ✓
    $(CH_3)_2NH$
  • B
    $CH_3NH_2$
  • C
    $(CH_3)_3N$
  • D
    $C_6H_5NH_2$
✓

Answer

Correct option: A.
$(CH_3)_2NH$
a
Order of basic strength of aliphatic amine in aqueous solution is as follows (order of $K_{b}$ )

$\left(\mathrm{CH}_{3}\right)_{2} \bar {N}H>\mathrm{CH}_{3} \bar {N}H_{2}>$$\left(CH_{3}\right)_{3} \bar {N}>\mathrm{C}_{6}\ mathrm{H}_{5} \bar {N} \mathrm{H}_{2}$

As we know $\mathrm{pk}_{\mathrm{b}}=-\log \mathrm{K}_{\mathrm{b}}$

So $ (CH_3) _{2}$  $NH$ will have smallest $pK_{b}$ value. In the case of phenylamine, $N$ is attached to $s p^{2}$ hybridised carbon, hence it has highest $p K_{b}$ and least basic strength.

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