Amide
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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.
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Overview
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 Brønsted 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 Specifically, an amide is a derivative of a carboxylic acid in which the hydroxyl group has been replaced by an amine or ammonia.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.
Amide linkages
An amide linkage is kinetically stable to hydrolysis. However, it can be hydrolysed in boiling alkali. Unlike the hydrolysis of esters, the kinetics of amide hydrolysis is third order- first order with respect to the amide and second order with respect to hydroxide. 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.
Derivatives
Sulfonamides are analogs of amides in which the atom double bonded to oxygen is sulfur rather than carbon.
Naming
- Example: CH3CONH2 is named acetamide or ethanamide
- Other examples: propan-1-amide, N,N-dimethylpropanamide
- For more detail see IUPAC_nomenclature#Amines_and_Amides
References
- IUPAC Compendium of Chemical Terminology (http://www.chemsoc.org/chembytes/goldbook/)da:Amid
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