amidines

Amidines are a class of organic compounds that contain the functional group RC(=NH)NR'R'', where a central carbon is double-bonded to an imine nitrogen and singly bonded to an amine nitrogen. The group can be represented as RC(=NH)NR2 and is often described as having substantial resonance, giving amidinium-like character in many contexts. The neutral form is the common reference structure, with the adjacent nitrogen atoms bearing lone pairs that render amidines relatively basic.

Aldehydes or ketones, ammonia or primary/secondary amines, and cyanamide react in a condensation known as the Debus–Radziszewski synthesis to give amidines. This route is widely used in laboratories to prepare aryl- and alkyl-substituted amidines. Other methods include direct amidination of nitriles with amines under dehydrating conditions, or conversion of imidoyl chlorides to the corresponding amidines by treatment with amines. Numerous variations exist to accommodate sensitive substrates or to introduce diverse substituents on either the carbon or nitrogen atoms.

Amidines are among the stronger neutral organic bases. Their conjugate acids typically have pKa values around 11–13, and they readily form amidinium salts. They are good ligands, able to bind metal centers through the two nitrogen atoms, and they appear as motifs in medicinal chemistry to enhance basicity, oral bioavailability, or binding interactions. Simple examples include benzamidine and related aryl- and alkyl-substituted amidines, which find use in catalysis, synthesis, and drug design.