From left to right a β-lactam, γ-lactam and δ-lactam
A lactam is a cyclic amide in organic chemistry. The ring is formed by internal amide formation of a carboxylic acid with an amino group in its own molecule. The substance Caprolactam is an example of this class of compounds, as well as the many β-lactam antibiotics, or Penicillins. The Greek letter as a prefix indicates the carbon atom in which the open chain compound contains the amino group. The first carbon atom is α, the second β, and so on the Greek alphabet. Thus, β-lactam has the nitrogen atom, the carbon atom of the acid group and two more carbon atoms in the ring, thus together four atoms in the ring; γ-lactam has the nitrogen atom, the carbon atom of the acid group and three more carbon atoms in the ring, thus a 5-ring; δ-lactam in the same way forms a 6-ring; an ε-lactam, as the caprolactam has seven atoms in the ring.
For caprolactam, the formation of the compound can be described as (although the technical preparation of that particular lactam is usually different): H2N- (CH2) 5COOH → H2O + formation of caprolactam from ε-aminocaproic acid (or 6-aminohexanoic acid)
Together with the lactones (internal esters and sultons (internal sulfonic acid esters)) the lactams form a group of synthetic and sometimes technically important intermediates.
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