Amide (chemical functional group and ion)

Structure and properties

Organic amides show strong resonance between the nitrogen lone pair and the carbonyl group, which gives the C–N bond partial double‑bond character and often enforces planarity at the amide bond. This resonance reduces basicity and nucleophilicity relative to amines and promotes hydrogen bonding when N–H groups are present. Amides are classed as primary, secondary or tertiary depending on N–H substitution; cyclic amides are called lactams.

Inorganic amides

The amide ion, NH2−, is a strong base and nucleophile present in metal amides such as sodium amide (NaNH2) and lithium diisopropylamide (LDA). These reagents are widely used for deprotonation, elimination and other transformations in organic synthesis. Metal amides have ionic or covalent character depending on the metal and ligands.

Biological and materials importance

Peptide bonds linking amino acids are amide linkages and form the backbone of proteins; the planarity and partial double‑bond character of the amide influence protein folding and secondary structure. Synthetic polyamides, including nylons and aramids (e.g. Kevlar), rely on repeated amide bonds to produce strong, high‑performance polymers.

Synthesis and reactions

Common routes to amides include condensation of carboxylic acid derivatives (acid chlorides, anhydrides, activated esters) with amines and modern coupling methods used in peptide synthesis. Amides undergo hydrolysis to carboxylic acids and amines under acidic or basic conditions, can be reduced to amines, and participate in rearrangements and dehydrations under suitable conditions.

Analysis and safety

Amide groups are readily identified by spectroscopy: carbonyl and N–H features appear in infrared and NMR spectra and X‑ray crystallography can show amide planarity. Some amides (for example acrylamide) have toxicity concerns and metal amide reagents are highly reactive; appropriate precautions and handling protocols are required.