In chemistry, an amide is either an organic functional group with a nitrogen atom bonded to a carbonyl carbon atom or a compound containing nitrogen bonded to carbon (or another atom) and two other groups. An amide is a derivative of an oxoacid [RnE(=O)xOH), where n and x are 1 or 2, E is an element, and R is hydrogen or an organic group), where an amine group (-NR2) replaces the hydroxyl group (-OH). So, an amide is either the functional group RnE(=O)xNR2 or a compound that contains this group.
Organic and Inorganic Amides
In organic chemistry, an amide derives from ammonia or an amine, where an acyl group (RCO-) replaces hydrogen. Also in organic chemistry, an amide is a functional group with a single covalent bond between the nitrogen atom and carbonyl carbon.
However, there are also inorganic amides. Here, the compound typically derives from ammonia (NH3) and a metal (or other non-carbon atom) replaces hydrogen. While organic amides are covalent compounds, inorganic amides may be either ionic or covalent, depending on the nature of the atom.
There are a few ways of classifying amides that depend on the structure of the group/compound or the identity of the atom bonded to the nitrogen.
- An amide is primary (1°), secondary (3°), or tertiary (3°), depending on whether the amine takes the form -NH2, -NHR, or -NRR’ (where R and R’ are groups rather than hydrogen atoms).
- The amide group consists of a nitrogen atom bonded to a carbonyl group, with the formula -C(=O)N=.
- A simple amide is one in which the nitrogen attaches to the carbonyl carbon and two hydrogen atoms. The suffix -amide replaces the -ic or -oic name of the carboxylic acid. For example, formic acid becomes formamide.
- A substituted amide is one where one or both of these bonds are to alkyl or aryl groups.
- A lactam or cyclic amide is a cyclic compound with the amide group [-C(=O)N-) within the ring.
- Carboxamides or organic amides are amides where E = carbon. The general formula of a carboxamide is RC(=O)NR2.
- A phosphoramide is an amide where E = phosphorus, with the formula R2P(=O)NR2.
- In sulfonamides, E = sulfur, with the formula RS(=O)NR2.
- While most amides are covalent compounds, a metal amide is an ionic compound containing the azanide anion (H2N–).
- An amide linkage refers to the carbonyl carbon bond to nitrogen. When this bond appears in a protein molecule, it is called a peptide linkage. When the bond is in a side chain (as in the amino acids asparagine and glutamine), it is an isopeptide bond.
Examples of Amides
Examples of commercially important amides include acetamide or ethanamide (CH3CONH2), dimethylformamide [HCON(CH3)2], urea or carbamide [CO(NH2)2), penicillin and other sulfa drugs, acetaminophen or paracetamol, LSD, Kevlar, and nylon. Amides find use in making plastics and other polymers, as drugs, as solvents, and as precursors to other compounds.
Amides generally are soluble in water because of hydrogen bonding and high polarity. Typically, the have high melting and boiling points. Most amides are solid at room temperature and are very weak bases. They readily undergo chemical reactions.
Amide vs Amine
Amides and amines are both nitrogen-based functional groups and compounds. However, an amide contains a carbonyl (C=O) or other atom double-bonded to oxygen that is linked to nitrogen, while an amine has an alkyl group (CnH2n+1) or non-carbon atom attached to nitrogen.
This gives amines a lower melting and boiling point than amides. Amines tend to be liquids or gases at room temperature. Amines are much stronger bases than amides. Examples of amines include aniline (C6H5NH2), chloramine (NH2Cl), and ethanolamine (C7H7NO).
- de Figueiredo, Renata Marcia; Suppo, Jean-Simon; Campagne, Jean-Marc (2016). “Nonclassical routes for amide bond formation.” Chemical Reviews. 116 (19): 12029-12122. doi:10.1021/acs.chemrev.6b00237
- IUPAC (1997). Compendium of Chemical Terminology (2nd ed.) (the “Gold Book”). Oxford: Blackwell Scientific Publications. ISBN 0-9678550-9-8.
- March, Jerry (2013). Advanced Organic Chemistry, Reactions, Mechanisms and Structure (7th ed.). Wiley. ISBN 978-0470462591.
- Monson, Richard (1971). Advanced Organic Synthesis: Methods and Techniques. Academic Press. ISBN 978-0124336803.
- Montalbetti, Christian A. G. N.; Falque, Virginie (2005). “Amide bond formation and peptide coupling”. Tetrahedron. 61 (46): 10827–10852. doi:10.1016/j.tet.2005.08.031