Dimer
Definition and meaning of Dimer in chemistry.
A dimer is a molecule made of two identical or very similar smaller units joined together. Those smaller units are called monomers. The two monomers can be linked by strong chemical bonds or by weaker forces like hydrogen bonds.
In more detail
Dimers can form in two main ways. In covalent dimerization, two monomer molecules react and form new chemical bonds, creating one larger molecule. In noncovalent dimerization, two molecules stick together through weaker attractions, such as hydrogen bonds, without forming any new bonds.
Noncovalent dimers can often break apart again if the temperature, concentration, or solvent changes. This makes the process reversible. A dimer can also form from two different but related molecules.
This mixed pairing is called a heterodimer, while a pairing of two identical units is called a homodimer. Dimer formation matters in many areas of chemistry. It changes how a gas behaves, since a dimer acts like one larger particle instead of two small ones, which can throw off vapor density measurements.
In living cells, many proteins only work correctly once two copies join into a dimer. Chemists sometimes force dimer formation on purpose, using special reagents to build larger, more complex molecules from simple starting materials. Blocking a protein dimer that a disease depends on is also a strategy used in modern drug design.
Some hormone receptors on cell surfaces only switch on once two receptor molecules pair up into a dimer, triggering the signal inside the cell.
Key facts
| Field | General Chemistry |
|---|---|
| General formula | (monomer)2 |
| Bonding types | Covalent or noncovalent (hydrogen bonds, van der Waals) |
| Reversibility | Noncovalent dimers often break apart and re-form |
| Naming | Homodimer (identical units) or heterodimer (related but different units) |
| Common example | 2 NO2 in balance with N2O4 (dinitrogen tetroxide) |
Acetic acid molecules often pair up in nonpolar solvents and in the gas phase. Two molecules link through two hydrogen bonds, forming a ring-shaped dimer written as (CH3COOH)2. Because of this pairing, acetic acid vapor behaves as if its molar mass were roughly double that of a single molecule.
Frequently asked questions
How is a dimer different from a polymer?
A dimer is made of exactly two monomer units. A polymer is made of many repeating monomer units, often thousands, linked in a chain or network.
Must the two units in a dimer be identical?
No. A homodimer forms from two identical monomers, while a heterodimer forms from two different but chemically related molecules, as seen in many dimeric proteins.
Why does dimer formation matter for gas measurements?
A dimer moves and behaves like one particle instead of two. If a gas partly dimerizes, its measured molar mass or vapor density can come out higher than expected for the single monomer.
Related terms
Sources & references
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