Propylamine (C3H7NH2) can form a maximum of two hydrogen bonds. One hydrogen bond is formed between the hydrogen atom of the amino group (-NH2) and a lone pair of electrons on the nitrogen atom of another propylamine molecule. The other hydrogen bond is formed between the hydrogen atom of the amino group and a lone pair of electrons on the oxygen atom of a water molecule.

Other molecules that can form hydrogen bonds include:

* Alcohols: Alcohols (R-OH) can form hydrogen bonds between the hydrogen atom of the hydroxyl group (-OH) and a lone pair of electrons on the oxygen atom of another alcohol molecule or a water molecule.

* Carboxylic acids: Carboxylic acids (R-COOH) can form hydrogen bonds between the hydrogen atom of the carboxyl group (-COOH) and a lone pair of electrons on the oxygen atom of another carboxylic acid molecule or a water molecule.

* Amides: Amides (R-CONH2) can form hydrogen bonds between the hydrogen atom of the amide group (-CONH2) and a lone pair of electrons on the nitrogen atom of another amide molecule or a water molecule.

* Ketones: Ketones (R-C(=O)-R') can form hydrogen bonds between the hydrogen atom of the carbonyl group (C=O) and a lone pair of electrons on the oxygen atom of another ketone molecule or a water molecule.

* Aldehydes: Aldehydes (R-CHO) can form hydrogen bonds between the hydrogen atom of the carbonyl group (C=O) and a lone pair of electrons on the oxygen atom of another aldehyde molecule or a water molecule.