Question

Arrange the following in the correct order of their basic character in aqueous medium
I ${NH}_3$
II ${CH}_3{NH}_2$
III ${\left({CH}_3\right)}_{2}NH$
IV ${\left({CH}_3\right)}_{3}N$

• A. IV > III > II > I
• B. III>IV>II>I
• C. III>II>IV>I
• D. I>II>III>IV

Answer 1

Answer: (C)

III>II>IV>I

In aqueous medium, in general, amines are more basic than ammonia.
Further, among the amines, secondary amines are most basic and then tertiary amines and then primary amines.
So the order is as follows : secondary > tertiary > primary > ammonia
Now, we give the reasons :
first amines are more basic than ammonia because of +I effect of the alkyl groups in amines.
+I effect increases basicity.
Next we may think that the order should be tertiary amines > secondary amines > primary amines
But this is not true in aqueous medium.
In water, we also have to consider the factor of solvation of the conjugate acid.
The conjugate acid of tertiary amine is less stable than the conjugate acid of secondary amine due to steric effect.
As a result, secondary amines are more basic than tertiary amines.
So, C is correct