Amide

An amide (/ˈæmaɪd/ or /ˈæmɪd/ or /ˈeɪmaɪd/), 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). 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. The remainder of this article is about the carbonyl–nitrogen sense of amide. The simplest amides are derivatives of ammonia wherein one hydrogen atom has been replaced by an acyl group. The ensemble is generally represented as RC(O)NH2 and is described as a primary amide. Closely related and even more numerous are secondary amides which can be derived from primary amines (R′NH2) and have the formula RC(O)NHR′. Tertiary amides are commonly derived from secondary amines (R′R″NH) and have the general structure RC(O)NR′R″. Amides are usually regarded as derivatives of carboxylic acids in which the hydroxyl group has been replaced by an amine or ammonia. The lone pair of electrons on the nitrogen is delocalized into the carbonyl, thus forming a partial double bond between N and the carbonyl carbon. Consequently, the nitrogen in amides is not pyramidal. It is estimated that acetamide is described by resonance structure A for 62% and by B for 28% (which does not sum to 100% because there are additional resonance forms that are not depicted in the above Figure). One final thing to note when looking at the bonds of an amide is that there is also a hydrogen bond present between the active groups hydrogen and nitrogen atoms. In the usual nomenclature, one adds the term 'amide' to the stem of the parent acid's name. For instance, the amide derived from acetic acid is named acetamide (CH3CONH2). IUPAC recommends ethanamide, but this and related formal names are rarely encountered. When the amide is derived from a primary or secondary amine, the substituents on nitrogen are indicated first in the name. Thus, the amide formed from dimethylamine and acetic acid is N,N-dimethylacetamide (CH3CONMe2, where Me = CH3). Usually even this name is simplified to dimethylacetamide. Cyclic amides are called lactams; they are necessarily secondary or tertiary amides. Functional groups consisting of –P(O)NR2 and –SO2NR2 are phosphonamides and sulfonamides, respectively. Some chemists make a pronunciation distinction between the two, saying /əˈmiːd/ for the carbonyl–nitrogen compound and /ˈeɪmaɪd/ (listen) for the anion. Others replace one of these with /ˈæmɪd/, while still others pronounce both /ˈæmɪd/, making them homonyms.