Question

Arrange the following compounds in increasing order of their boiling points:
A.\[{\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{CHO}}\]
B.\[{\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{OH}}\]
C.\[{{\text{C}}_2}{{\text{H}}_5}{\text{O}}{{\text{C}}_2}{{\text{H}}_5}\]
D.\[{\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_3}\]

Answer 1

Hint: Organic compounds with stronger force of attraction between their molecules have higher melting and boiling point. Attraction like intermolecular hydrogen bonding increases attraction force between molecules several times thereby corresponds to a higher melting and boiling point.

Complete step by step answer:
Boiling point of ionic compounds is greater than that of covalent compounds. So, we can say that the boiling point of organic compounds increases with increase in the bond polarity of the organic compounds. Also the greater force of attraction either intermolecular or interatomic between the molecules corresponds to higher boiling point.
Given organic compounds as given in question are \[{\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{CHO}}\] (Aldehyde Butanal), \[{\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{OH}}\] (Alcohol Butanol), \[{{\text{C}}_2}{{\text{H}}_5}{\text{O}}{{\text{C}}_2}{{\text{H}}_5}\] (Diethyl ether), \[{\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_3}\] (Alkane Butane).

In the case of alcohol, due to the formation of hydrogen bonding between the molecules and polar nature, they have a much greater boiling point than aldehydes, ether and alkane. In alcohol, intermolecular hydrogen bonding exists. On the other hand, aldehydes have higher boiling point than ethers and hydrocarbons like alkane due to the weak intermolecular dipole-dipole interaction between the molecules of aldehydes. This dipole-dipole interaction is a type of vanderwall force which exists between dipole and dipole. On the other way, ethers do not have any hydrogen bonding and that too has only little intermolecular association, but have higher boiling point than hydrocarbon like alkane.

So, the correct order in increasing boiling point is: \[{\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_3} < {{\text{C}}_2}{{\text{H}}_5}{\text{O}}{{\text{C}}_2}{{\text{H}}_5} < {\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{CHO}} < {\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{OH}}\] or we can say \[{\text{Alkane}} < {\text{Ether}} < {\text{Aldehyde}} < {\text{Alcohol}}\] .

Thus, the correct answer is \[{\text{D}} < {\text{C}} < {\text{A}} < {\text{B}}\] .

Note: Boiling point is the temperature at which the vapour pressure of the liquid becomes equal to atmospheric pressure. At this state, liquid converts to vapour state. Melting point is the temperature at which a liquid is converted to solid state.