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Q.
n-Butylamine $(I)$, diethylamine $(II)$ and $N, N$-dimethylethylamine $(III)$ have the same molar mass. The increasing order of their boiling point is
The boiling points of amines depends upon their degree of association and the degree of association is further depends upon the extent of H-bonding. Since $ 1{}^\circ $ amines have two, $ 2{}^\circ $ amines have one while 3° amines have no hydrogen atoms linked to nitrogen, therefore among isomeric amines, $ 1{}^\circ $ amines have the highest, while $ 3{}^\circ $ amines have the lowest boiling point. Thus, the increasing order of boiling point is
$ \underset{N,\text{ }N-dimethylethylamine\text{ }(III)}{\mathop{C{{H}_{3}}\overset{\begin{smallmatrix} C{{H}_{3}} \\ | \end{smallmatrix}}{\mathop{N}}\,C{{H}_{2}}C{{H}_{2}}}}\, $
$ \underset{diethylamine\text{ }(II)}{\mathop{ < C{{H}_{3}}C{{H}_{2}}NHC{{H}_{2}}-C{{H}_{3}}}}\, $ $ \underset{n-butylamine\text{ }(I)}{\mathop{ < C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}C{{H}_{2}}N{{H}_{2}}}}\, $