Macrocycle

As Macrocyclic compounds (short: macrocycles, singular: macrocycle ) is called in the chemical compounds whose atoms are arranged so that they form a large ring.

From the cyclic compounds, they differ by the number of ring-forming atoms, so the size of the ring. An exact definition of when a ring is considered macrocycle does not exist. In the laboratory daily so molecules are referred to with ring sizes from about eight atoms. Regardless of the assignment to the macrocyclic compounds also small rings may be present in the same molecule.

Synthesis of macrocyclic compounds

The selective synthesis of macrocycles often presents a challenge, since the intramolecular ring closure reaction always competes with intermolecular coupling reaction. Useful for increasing the yield of the macrocyclic molecule, can be the application of the Ziegler- Ruggli dilution principle.

Properties

Large ring-shaped molecules, in contrast to small-ring virtually no ring strain. You can easily take a variety of conformations, since at least the single bonds in the ring more limited but with increasing ring size are always easier to rotate.

Do individual ring atoms donor properties, so can also act as chelating macrocycles - an example of this are the crown ethers used for masking anions.

Of particular importance is the macrocycles in the field of supramolecular chemistry, since these compounds are used there to ( catenanes ) or dumbbell-shaped ( rotaxanes ) to synthesize, for example, chain-like assemblies.

Occurrence

Macrocyclic compounds occur for example in the form of cyclodextrins or cyclic peptides in living nature. Inorganic compounds are partly present in large rings, examples of this are the various annular modifications of sulfur such as cyclooctasulfur. Individual macrocycles such as narbomycin have antibiotic properties and are therefore used as a drug.