Question

Arrange the following.

In increasing order of boiling point C₆H₅OH, (CH₃)₂NH, C₂H₅NH₂.

Answer 1

Since the electronegativity of O is higher than that of N, therefore, alcohols form stronger H-O bonds than amines. In other words, the boiling points of alcohols are higher than those of amines of comparable molecular masses. Therefore the boiling point of C₆H₅OH (46) is higher than those of (CH₃)₂NH (45) and C₂H₅NH₂ (45).

Further, the extent of H-bonding depends upon the number of H-atoms on the N-atom. Therefore 1° amine with two H-atoms on the N-atom has higher boiling points than 2° amines having only one H-atom. Therefore the boiling point of C₂H₅NH₂ is higher than that of(CH₃)₂NH.

The increasing order of boiling point is, (CH₃)₂NH < C₂H₅NH₂ < C₆H₅OH.