= Carboxamidine
A <carboxamidine> is a carbon-centred <amidine>, with the N-unsubstituted pattern $\mathrm{R-C(=NH)-NH_2}$. 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.<Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 by IUPAC>[P-66.4.1, opening definition; P-66.4.1.4.1, N-substituted amidines]{ref}
For an atom-count example, $\mathrm{CH_3-C(=NH)-NH_2}$ has <molecular formula> $\mathrm{C_2H_6N_2}$. Replacing one amino hydrogen by $\mathrm{CH_3}$ gives $\mathrm{CH_3-C(=NH)-NH-CH_3}$, with <molecular formula> $\mathrm{C_3H_8N_2}$. The change adds $\mathrm{CH_2}$ 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.<Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 by IUPAC>[P-66.4.1.1, Suffixes for amidines]{ref}
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