Question

The boiling point of butan-2-one ( 79.64^oC ) is significantly higher than the boiling point of diethyl ether ( 34.6^OC), even though both compounds exhibit dipole–dipole interactions and have comparable molecular weights. Offer an explanation.

Short answer

The lone pairs of oxygen in butan-2-one are less hindered, due to which it interacts more with other molecules. Thus, it has a high boiling point.

Step-by-step solution

Factors affecting the boiling point

The interaction between the molecules depends upon the hindrance around them. If there is more hindrance, then less interaction between the molecules takes place. Thus, the boiling point will also be less.

Explanation for higher boiling point

The structure of the given compounds are mentioned below:

Structures of butan-2-one and diethyl ether

Both compounds contain an oxygen atom. Oxygen is more crowded in diethyl ether, but less crowded in butan-2-one. As a result, lone pairs of oxygen in butan-2-one will interact more with other molecules, resulting in stronger forces.

Thus, the boiling point of butan-2-one is more than diethyl ether.