Organic compounds containing a ring of atoms in which the group –NH.CO.– forms part of the ring. Lactams can be formed by reaction of an –NH2 group in one part of a molecule with a –COOH group in the other to give a cyclic amide. They can exist in an alternative tautomeric form, the lactim form, in which the hydrogen atom on the nitrogen has migrated to the oxygen of the carbonyl to give –N=C(OH)–. The pyrimidine base uracil is an example of a lactam.
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