Why is the boiling point of propan-1-amine higher than that of chloroethane?
Propan-1-amine (CH3CH2CH2NH2) has a higher boiling point than chloroethane (CH3CH2Cl) because the molecules of propan-1-amine experience stronger intermolecular forces.
Propan-1-amine contains an N–H bond and a nitrogen atom with a lone pair of electrons. Therefore, propan-1-amine molecules can form hydrogen bonds with one another. Hydrogen bonding is a relatively strong intermolecular force and requires more energy to overcome.
Chloroethane does not contain an N–H or O–H bond, so its molecules cannot form hydrogen bonds with each other. The main intermolecular attractions are dipole–dipole forces and London dispersion forces, which are weaker overall than the hydrogen bonding between propan-1-amine molecules.
Therefore, more energy is required to separate the molecules of propan-1-amine. As a result, propan-1-amine has a higher boiling point than chloroethane.
Exam-style answer
Propan-1-amine has a higher boiling point because its molecules can form hydrogen bonds with each other due to the N–H bonds and the lone pair on nitrogen. Chloroethane cannot form hydrogen bonds and has weaker intermolecular attractions. Therefore, more energy is needed to overcome the intermolecular forces in propan-1-amine, giving it a higher boiling point.NCEA Level 3 Chemistry 2023