organic chemistry

According to the database in ChemDraw 12.0, the boiling point of Hexylamine (409K) is higher than that of Dipropylamine (387K).

However, the main reason for their difference in boiling points should not be as described by rhdiddl.
While Hexylamine has two N-H (lone-pair acceptor) and dipropylamine has only one N-H, the nitrogen atoms in both amines have only 1 lone-pair available for donation.
An (intermolecular) hydrogen bond forms when there is a pair of lone-pair donor and lone-pair acceptor.

In my opinion, the main reason for their difference in boiling points is the steric hindrance due to the alkyl group(s).
Hexylamine has one alkyl group attached to the nitrogen atom, while dipropylamine has two.
The more alkyl groups attached to the N atom there are, the larger steric hindrance there is, causing the lone-pair on N atom to be less available (OR the N-H on the molecules in vicinity to be harder to approach).
The alkyl groups act as a shield, warding off the approaching (hydrogen-bond-forming) N-H.

Hexylamine is CH3CH2CH2CH2CH2CH2NH2, a primary amine.

Dipropylamine is (CH3CH2CH2)2NH, a secondary amine.

Both of them have similar Molar Mass, 101.


The N–H bonds in amine compound can engage in hydrogen bonding.
Primary amines have two hydrogens i.e. 2 N–H bonds available for
hydrogen bonding, and therefore, such amines usually have higher boiling
points than isomeric secondary amines.

As hexylamine is a primary amine, it will have a higher boiling point than
dipropylamine, which is a secondary amine.

This can be seen from the following figures:
hexylamine's boiling point 131.5 °C
dipropylamine's boiling point 111 °C