General structure of (primary) diamines. The primary amino groups (NH2) are marked blue, R is a divalent organic radical (e.g. a para-phenylene group).

A diamine is an amine with exactly two amino groups. Diamines are used as monomers to prepare polyamides, polyimides, and polyureas. The term diamine refers mostly to primary diamines, as those are the most reactive.^[1]

In terms of quantities produced, 1,6-diaminohexane (a precursor to Nylon 6-6) is most important, followed by ethylenediamine.^[2] Vicinal diamines (1,2-diamines) are a structural motif in many biological compounds and are used as ligands in coordination chemistry.^[3]

Geminal diamines (1,1-diamines) are usually reactive intermediates in transimination reactions and the reduction of amidines, in aqueous conditions they preferentially eliminate the less basic amine to leave an iminium ion.^[4] Some stable geminal diamines have been isolated.^[5]

• 1 carbon: methylenediamine (diaminomethane) of theoretical interest only, but its hydrochloride can be used in the synthesis of amides.^[6]
• 2 carbon backbone: ethylenediamine (1,2-diaminoethane). Related derivatives include the N-alkylated compounds, 1,1-dimethylethylenediamine, 1,2-dimethylethylenediamine, ethambutol, tetrakis(dimethylamino)ethylene, TMEDA.

• 
  Ethylenediamine

• 3 carbon backbone: 1,3-diaminopropane (propane-1,3-diamine)
• 4 carbon backbone: putrescine (butane-1,4-diamine)
• 5 carbon backbone: cadaverine (pentane-1,5-diamine)

• 
  Cadaverine

• 6 carbon backbone: hexamethylenediamine (hexane-1,6-diamine)

Derivatives of ethylenediamine are prominent:

• 1,2-diaminopropane, which is chiral.
• 2,3-Butanediamine, two diastereomers, one of which is C₂-symmetric.
• Diphenylethylenediamine, two diastereomers, one of which is C₂-symmetric.
• 1,2-Diaminocyclohexane, two diastereomers, one of which is C₂-symmetric.
• trimethylhexamethylenediamine, several isomers

• 1,4-Diazacycloheptane

• 
  1,4-Diazacycloheptane

Xylylenediamines are classified as alkylamines since the amine is not directly attached to an aromatic ring.

• o-xylylenediamine or OXD
• m-xylylenediamine or MXD
• p-xylylenediamine or PXD

Three phenylenediamines are known:^[7]

• o-phenylenediamine or OPD
• m-phenylenediamine or MPD
• p-phenylenediamine or PPD. 2,5-diaminotoluene is related to PPD but contains a methyl group on the ring.

• 
  p-phenylenediamine

Various N-methylated derivatives of the phenylenediamines are known:

• dimethyl-4-phenylenediamine, a reagent.
• N,N'-di-2-butyl-1,4-phenylenediamine, an antioxidant.

Examples with two aromatic rings include derivatives of biphenyl and naphthalene:

• 4,4'-diaminobiphenyl
• 1,8-diaminonaphthalene

• Diamines at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
• Synthesis of diamines