LACTAM

Lactams 

Internal cyclic amides of amino carboxylic acids that contain a —CO—NH— group in the ring (I). The tautomeric, enol form of lactam is known as lactim (II):

 

Lactams are classified as β-, γ-, δ-, ε-, and so forth according to the type of amino carboxylic acids included in their composition, for example, β-propiolactam (III; melting point, 73°-74°C), γ-butyrolactam (IV; melting point, 24.6°C), and ε-caprolactam (V; melting point, 68°-69°C):

Lactams are primarily obtained by the cyclization of amino carboxylic acids or their derivatives [Y—(CH₂)_nNH₂, where Y = COOH, COOR, CONH₂, CN], as well as by the cyclization of amides of halogen carboxylic or hydroxycarboxylic acid [X—(CH₂)_nCONHR, where X = OH or a halogen]. An important method of obtaining lactam is the Beckmann rearrangement of cyclic ketoximes, which is used in the industrial preparation of ε-caprolactam.

Lactams readily undergo alkylation, acylation, and halogena-tion with retention of the ring. The lactam ring, however, is opened at the —CO—NH—bond during hydrolysis, ammonolysis, hydrogenolysis, and polymerization. For example, ε-caprolactam polymerization yields polycaproamide, from which nylon 6 fiber is made. Many lactams are biologically active substances (for example, a molecule of penicillin contains a β-propiolactam residue).

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,
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.
Reducing the Carbonyl in Lactam to CH2
The carbonyl of a lactam can be reduced to produce a heterocyclic ring. "Heterocyclic" refers to the presence of a non-carbon atom in the ring. It is thus easy to produce a four member ring containing a nitrogen atom, or a five member ring, a six member ring, and so on. Such rings often occur in very important organic compounds related to living things. There are heterocyclic rings in the active ingredients of a plethora of medications. There are a variety of methodologies for reducing the carbonyl. To visualize the end result, again refer to the image associated with this article.
Although it isn't obvious as drawn, the carbon-containing chain formed actually consists of six atoms, C-C-C-N-C-C. The oxygen is actually attached to the next-to-last carbon by a double-bond off to the side.  Utilizing different conditions can produce a polymeric product. The amino group of one molecule would react with the carboxylic acid of a different molecule, and so on.