Lactams

Lactams - Cyclic Amides
With some modification, a reaction may be carried out that generates a ring structure containing a similar linkage. Consider the result if two functional groups are a distance apart on the same molecule and react together. Consider, for instance, 4-aminobutyric acid, H₂N-CH₂CH₂CH₂-COOH. If reacted utilizing the proper conditions,²
H₂N-CH₂CH₂CH₂-COOH → 5-member ring + HOH (see associated image).
The amino group at one end reacts with the carboxylic acid group at the other, closing the molecule to form the ring. The ring structure is called a lactam. The type of lactam is designated by using a Greek letter prefix that indicating the number of carbons in the ring, not counting the carbonyl group. For instance, if there are two such carbons, the prefix is beta (the 2nd letter of the alphabet)-if there are four, the prefix is delta, and so on. The ring formed in the above reaction is a gamma-lactam. It's name is based on the number of carbon atoms in the skeleton-in this instance, butyrolactam. There are other ways of naming the structure, one of which is 2-pyrollidinone.