Amide (functional group)

In chemistry, the term amide is a compound with the functional group R_nE_xNR₂, where x is not zero, E is some element, and each R represents an organic group or hydrogen. It is a derivative of an oxoacid R_nE_xOH with an hydroxy group –OH replaced by an amine group –NR₂.
Some important subclasses are

carboxamides, or organic amides, where E = carbon, with the general formula RCNR₂.
phosphoramides, where E = phosphorus, such as R₂PNR₂
sulfonamides, where E = sulfur, namely RS₂NR₂

The term amide may also refer to

amide group, a functional group –CN= consisting of a carbonyl adjacent to a nitrogen atom.
cyclic amide or lactam, a cyclic compound with the amide group –CN– in the ring.
metal amide, an ionic compound with the azanide anion H₂N⁻ or to a derivative thereof R₂N⁻.

There is also a neutral amino radical and a positively charged NH₂⁺ ion called a nitrenium ion, but both of these are very unstable.