An amide (/ˈæmaɪd/ or /ˈæmɪd/ or /ˈeɪmaɪd/),[1][2][3] also known as an acid amide, is a compound with the functional group RnE(O)xNR′2 (R and R′ refer to H or organic groups). Most common are carboxamides (organic amides) (n = 1, E = C, x = 1), but many other important types of amides are known, including phosphoramides (n = 2, E = P, x = 1 and many related formulas) and sulfonamides (E = S, x = 2).[4] The term amide refers both to classes of compounds and to the functional group (RnE(O)xNR′2) within those compounds. Amide can also refer to azanide (the anion H2N−, conjugate base of ammonia) or to an organic amine (an anion R2N−). For discussion of these "anionic amides", see Alkali metal amides. Due to the dual use of the word 'amide', there is debate as to how to properly and unambiguously name the derived anions of amides in the first sense (i.e., deprotonated acylated amines), a few of which are commonly used as nonreactive counterions.[5] The remainder of this article is about the carbonyl–nitrogen sense of amide.