Carboxamide

A carboxamide is an amide of a carboxylic acid, with a carbonyl group directly bonded to nitrogen. Its general connectivity is $\mathrm{R}-\mathrm{C}(=\mathrm{O})-\mathrm{N}{\mathrm{R}}^{\prime }{\mathrm{R}}^{\prime \prime }$, where the substituents shown can include hydrogen. The term identifies a class of compounds or a structural unit; amide bond identifies the carbonyl C–N bond within it.^[ref]

For example, acetamide, $\mathrm{C}{\mathrm{H}}_3\mathrm{C}(=\mathrm{O})\mathrm{N}{\mathrm{H}}_2$, contains one carboxamide group. Replacing an N–H covalent bond by an N–C covalent bond can leave the defining carbonyl C–N connectivity intact. Conversely, replacing the carbonyl oxygen by another group changes the functional class even though a C–N bond remains. Connectivity, rather than merely an inventory of elements, supplies the classification.

A formal atom balance illustrates carboxamide hydrolysis:Both sides contain two carbons, seven hydrogens, one nitrogen and two oxygens. The equation balances neutral molecular formulas; the actual reaction products can be protonated or deprotonated according to pH. It does not assert that mixing neutral reactants gives rapid conversion. Ordinary amide hydrolysis needs suitable conditions or enzyme catalysis, consistent with the persistence of peptide bonds in water.^[ref]