Question

Arrange the following in order of increasing boiling point. 

Answer 1

Ans. IV < II < III < I

Explanation

Among the given compounds, it is clear that CH₃CH₂OH (I) and CH₃OCH₂CH₃ (III) will have a higher boiling point due to the presence of hydrogen bonding between the Oxygen (O) and Hydrogen (H) atoms.

Hydrogen bonding is a strong intermolecular force caused due to the dipole-dipole interaction between a hydrogen atom and a highly electronegative atom in the form of Oxygen, Chlorine or Fluorine.

In compound I the hydrogen atom is directly connected due to the oxygen atom, whereas in compound III the hydrogen atom is connected to the carbon atom which is directly connected to the oxygen atom. Hence, the hydrogen bonding forces in compound I would be greater than in compound III and hence the boiling point of I > III.

Now let us compare the two alkanes - butane (II) and propane (IV). Alkanes have London dispersion forces as the primary intermolecular force. Hence, more the number of hydrocarbon atoms present, the higher would be intermolecular force. Since, butane has a longer carbon chain than propane, hence the boiling point of II > IV.

So arranging the given compounds in order of increasing boiling point - IV < II < III < I.