n-butylamine(I), diethylamine (II) and N,N-dimethylethylamine (III) have the same molar mass. The increasing order of their boiling point is

Options

A. `III lt II lt I`
B. `I lt II lt III`
C. `II lt III lt I`
D. `II lt I lt III`

Answer

A

Explanation

`underset(n-"Butylamine (Primary amine)")(H_(3)C- CH_(2)- CH_(2)- CH_(2)- NH_(2))`
`underset("Diethylamine (Secondary amine")(CH_(3)CH_(2)- NH- CH_(2)- CH_(3))`
`underset("Ethyldimethylamine (Tertiary amine)")(CH_(3)- overset(overset(CH_(3))(|))(N)- C_(2)H_(5))`
Primary amines have two hydrogen atoms available for hydrogen bond formation, while `2^(@)` amines have only one hydrogen atom for hydrogen bond formation. `3^(@)` amines do not have intermolecular association due to absence of hydrogen atom. Thus, order of boiling point of isomeric amines is as follows: `3^(@) lt 2^(@) lt 1^(@) or III lt II lt I`