Question

Dimethyl ether and ethanol are isomers. Their boiling points are very different, however. Explain why these two compounds have dramatically different boiling points.

CH₃-O-CH₃ CH₃CH₂-OH

dimethyl ether, bp -24 °C ethanol, bp 78 °C

Short answer

Ethanol have hydrogen bonding while dimethyl ether shows weaker intermolecular forces of attraction.

Step-by-step solution

Step 1:

Dimethyl ether have weaker intermolecular forces (weak dipole-dipole interactions) which required less energy to overcome the bond when compared to ethanol. And there are no hydrogen atoms directly attached to oxygen to form hydrogen bonds.

Step 2:

Ethanol have stronger Hydrogen bonding (it can accept one H-bond, and can donate one H-bond) which require more energy to overcome this bonding, which leading to a higher boiling point than dimethyl ether.