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Amines — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryAmines1 Mark
MCQ
The correct order of basic strength is:
  • A
    $\mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2>\mathrm{CH}_3 \mathrm{NH}_2>\mathrm{NH}_3$
  • B
    $\mathrm{CH}_3 \mathrm{NH}_2>\mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2>\mathrm{NH}_3$​
  • ✓
    $\mathrm{CH}_3 \mathrm{NH}_2>\mathrm{NH}_3>\mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2$
  • D
    $\mathrm{NH}_3=\mathrm{CH}_3 \mathrm{NH}_2=\mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2$​
✓

Answer

Correct option: C.
$\mathrm{CH}_3 \mathrm{NH}_2>\mathrm{NH}_3>\mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2$
To determine the order of basicity of amines, we have to check for the availability of lone pair, means how easily the lone pair on the nitrogen atom is available for the attack of an electrophile.
$\mathrm{NH}_3 :-$ it has lone pair which is available on it.
$\mathrm{CH}_3 \mathrm{NH}_2 $- there is positive inductive effect of methyl group, so electron density on nitrogen is more than that of $\mathrm{NH}_3.$
$\mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2$ - the lone pair of nitrogen is taking part in resonance with benzene ring, so it is least available to the attack of an electrophile compared to others.
So, the order is $\mathrm{CH}_3 \mathrm{NH}_2>\mathrm{NH}_3>\mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2$.

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