In chemistry, the term amide has several meanings. It may refer to a particular inorganic anion, it may refer to a functional group found in organic compounds, or to compounds that contain this functional group.
The amide anion is the conjugate base of ammonia, NH2-. It is an extremely strong base, due to the extreme weakness of ammonia as a Bronsted acid.
Amides are the members of a group of chemical compounds containing nitrogen. Specifically, an amide is a derivative of a carboxylic acid in which the hydroxyl group has been replaced by an amine or ammonia.
Compounds in which a hydrogen atom on nitrogen from ammonia or an amine is replaced by a metal cation are also known as amides or azanides.
The amide functional group is:
Synthesis and breakdown
Amides are commonly formed from the reaction of a carboxylic acids with an amine:
This is the reaction that forms peptide bonds between amino acids. These amides can participate in hydrogen bonding as hydrogen bond acceptors and donors, but do not ionize in aqueous solution, whereas their parent acids and amines are almost completely ionized in solution at neutral pH.
Amide formation plays a role in the synthesis of some condensation polymers, such as nylon. Their breakdown is possible via amide hydrolysis.
An amide linkage is kinetically stable to hydrolysis. Amide linkages in a biochemical context are called peptide linkages. Amide linkages constitute a defining molecular feature of proteins, the secondary structure of which is due in part to the hydrogen bonding abilities of amides.
Sulfonamides are analogs of amides in which the atom double bonded to oxygen is sulfur rather than carbon.