Physical Properties of Amines

Amines are polar compounds with a lone pair on the nitrogen atom that governs the overall molecular dipole moment. They act as hydrogen bond acceptors in hydroxylic solvents.

Typically, low-molecular-weight amines—with fewer than five carbon atoms—are miscible in water or water-soluble. In comparison, high-molecular-weight amines are either sparingly or completely insoluble in water since the non-polar hydrocarbon chains are incompatible with polar solvents.

Both primary and secondary amines are hydrogen-bond donors and form intermolecular hydrogen bonds. Hydrogen bonding directly influences the observed trends in the boiling points.

Thus, primary amines—with two N–H bonds—have higher boiling points than isomeric secondary and tertiary amines.

Intermolecular hydrogen bonds in amines are comparatively weaker than the ones in alcohols.

So, primary and secondary amines have lower boiling points than their alcohol analogs but higher boiling points than the compounds incapable of hydrogen bonding.

Amines have characteristic odors. Simple amines have a typical fishlike smell, while some diamines have a pungent odor; the odor influences the common names of such amines.