 Amidine

An amidine is a nitrogen analogue of an oxoacid derivative. In ordinary organic-chemistry usage it most often means a carboxamidine, whose central carbon is bonded to two nitrogens, conventionally represented by $\mathrm{R}-\mathrm{C}(=\mathrm{N}{\mathrm{R}}_1)-\mathrm{N}({\mathrm{R}}_2){\mathrm{R}}_3$. The IUPAC class is broader than only carbon-centred examples, so the intended structural subclass should be stated.^[ref]

A simple unsubstituted-nitrogen pattern is $\mathrm{R}-\mathrm{C}(=\mathrm{NH})-\mathrm{N}{\mathrm{H}}_2$. Choosing $\mathrm{R}=\mathrm{C}{\mathrm{H}}_3$ gives $\mathrm{C}{\mathrm{H}}_3-\mathrm{C}(=\mathrm{NH})-\mathrm{N}{\mathrm{H}}_2$ and an atom count of ${\mathrm{C}}_2{\mathrm{H}}_6{\mathrm{N}}_2$. Compare an amide, $\mathrm{R}-\mathrm{C}(=\mathrm{O})-\mathrm{N}{\mathrm{H}}_2$: replacing the doubly bonded oxygen with an imino nitrogen changes the characteristic group. Similar spelling does not make the two classes chemically identical.

Imidoesters react with amines to give amidines. This conversion connects a functional-group definition with experimental protein cross-linking, where amino groups on a protein can be modified by an appropriate reagent.^[ref] The structural pattern alone does not specify one reaction rate or one acid–base constant for every substituted amidine.