 Carboxamidine

A carboxamidine is a carbon-centred amidine, with the N-unsubstituted pattern $\mathrm{R}-\mathrm{C}(=\mathrm{NH})-\mathrm{N}{\mathrm{H}}_2$. More generally, substituents may replace hydrogens on either nitrogen. Its defining carbon is attached to an imino nitrogen and an amino nitrogen; an amide instead has a doubly bonded oxygen at the corresponding position.^[ref]

For an atom-count example, $\mathrm{C}{\mathrm{H}}_3-\mathrm{C}(=\mathrm{NH})-\mathrm{N}{\mathrm{H}}_2$ has molecular formula ${\mathrm{C}}_2{\mathrm{H}}_6{\mathrm{N}}_2$. Replacing one amino hydrogen by $\mathrm{C}{\mathrm{H}}_3$ gives $\mathrm{C}{\mathrm{H}}_3-\mathrm{C}(=\mathrm{NH})-\mathrm{NH}-\mathrm{C}{\mathrm{H}}_3$, with molecular formula ${\mathrm{C}}_3{\mathrm{H}}_8{\mathrm{N}}_2$. The change adds $\mathrm{C}{\mathrm{H}}_2$ overall because the new methyl group replaces a hydrogen. This bookkeeping illustrates N-substitution without treating a structural drawing as a measured reaction yield.

Class names and preferred naming suffixes should also be distinguished. The IUPAC recommendations retain the generic class description but use the suffixes -imidamide and -carboximidamide in the specified nomenclature, and distinguish the amino and imino positions by N and N′. Calling a substance a carboxamidine therefore does not prescribe the suffix in its preferred systematic name.^[ref]