An amide ( or or ),〔http://www.collinsdictionary.com/dictionary/english/amide〕〔http://www.oxforddictionaries.com/us/definition/english/amide〕 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 the conjugate base of ammonia (the anion H2N−) or of an organic amine (an anion R2N−). For discussion of these "anionic amides", see Alkali metal amides.
The remainder of this article is about the carbonyl-nitrogen sense of ''amide''.
==Structure and bonding==
The simplest amides are derivatives of ammonia wherein one hydrogen atom has been replaced by an acyl group.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. Closely related and even more numerous are amides derived from primary amines (R'NH2) with the formula RC(O)NHR'. Amides are also commonly derived from secondary amines (R'R
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%.
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