In chemistry and biochemistry, an oligomer () is a molecule that consists of a few which could be derived, actually or conceptually, from smaller molecules, monomer.[Quote: Oligomer molecule: A molecule of intermediate relative molecular mass, the structure of which essentially comprises a small plurality of units derived, actually or conceptually, from molecules of lower relative molecular mass.] The name is composed of Greek language elements , "a few" and , "parts". An adjective form is oligomeric.[
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The oligomer concept is contrasted to that of a polymer, which is usually understood to have a large number of units, possibly thousands or millions. However, there is no sharp distinction between these two concepts. One proposed criterion is whether the molecule's properties vary significantly with the removal of one or a few of the units.[
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An oligomer with a specific number of units is referred to by the Greek prefix denoting that number, with the ending -mer: thus dimer, trimer, tetramer, pentamer, and hexamer refer to molecules with two, three, four, five, and six units, respectively. The units of an oligomer may be arranged in a linear chain (as in melam, a dimer of melamine); a closed ring (as in 1,3,5-trioxane, a Cyclic compound trimer of formaldehyde); or a more complex structure (as in tellurium tetrabromide, a tetramer of with a cube-like core). If the units are identical, one has a homo-oligomer; otherwise one may use hetero-oligomer. An example of a homo-oligomeric protein is collagen, which is composed of three identical protein chains.
Some biologically important oligomers are macromolecules like or nucleic acids; for instance, hemoglobin is a protein tetramer. An oligomer of is called an oligopeptide or just a peptide. An oligosaccharide is an oligomer of (simple sugars). An oligonucleotide is a short single-stranded fragment of nucleic acid such as DNA or ribonucleic acid, or similar fragments of analogs of nucleic acids such as peptide nucleic acid or .
The units of an oligomer may be connected by , which may result from bond rearrangement or condensation reactions, or by weaker forces such as .
The term multimer () is used in biochemistry for oligomers of proteins that are not covalently bound. The major capsid protein VP1 that comprises the shell of polyomavirus is a self-assembling multimer of 72 pentamers held together by local electric charges.
Many are oligomeric, such as liquid paraffin. Plasticizers are oligomeric widely used to soften thermoplastics such as PVC. They may be made from monomers by linking them together, or by separation from the higher fractions of crude oil. Polybutene is an oligomeric oil used to make putty.
Oligomerization is a chemical process that converts monomers to macromolecular complexes through a finite degree of polymerization.[ Telomerization is an oligomerization carried out under conditions that result in chain transfer, limiting the size of the oligomers.]
Green oil
In the oil and gas industry, green oil refers to oligomers formed in all C2, C3, and C4 hydrogenation reactors of ethylene plants and other petrochemical production facilities; it is a mixture of C4 to C20 unsaturated and reactive components with about 90% aliphatic diene and 10% of alkanes plus alkenes.
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