Macrocyclic compounds
In chemistry , macrocyclic compounds (short: macrocycles , singular: macrocycle ) are compounds whose atoms are arranged in such a way that they form a large ring.
They differ from cyclic compounds in the number of ring-forming atoms, i.e. the size of the ring. An exact definition of when a ring is considered a macrocycle does not exist. In everyday laboratory work, it refers to molecules with ring sizes of around eight atoms or more. Independent of the assignment to the macrocyclic compounds, small rings can also be present in the same molecule.
Synthesis of macrocyclic compounds
The targeted synthesis of macrocycles is often a challenge, as the intramolecular ring closure reaction always competes with an intermolecular coupling reaction . The application of the Ziegler-Ruggli dilution principle can be helpful in increasing the yield of the macrocyclic molecule .
properties
In contrast to small rings, large ring-shaped molecules have practically no ring tension . They can easily adopt a variety of conformations , since at least the single bonds in the ring are limited, but the more the ring size increases, they can be turned more easily.
If individual ring atoms have donor properties, the macrocycles can also act as chelating ligands - an example of this are the crown ethers used to mask anions .
Macrocycles are of particular importance in the field of supramolecular chemistry , as these compounds are used there to synthesize , for example, chain-shaped ( catenanes ) or dumbbell-shaped ( rotaxanes ) assemblies.
Occurrence
Macrocyclic compounds occur in nature, for example, in the form of cyclodextrins or cyclopeptides . Also inorganic compounds are partly present in large rings, examples of this are the various modifications of the annular sulfur such as cyclooctasulfur. Individual macrocycles such as narbomycin have antibiotic properties and are therefore used as medicinal substances .
See also
literature
- James E. Huheey, Ellen A. Keiter, Richard Keiter: Inorganic Chemistry: Principles of Structure and Reactivity. , Walter de Gruyter Berlin 2003, ISBN 3-11-017903-2 ( limited preview in the Google book search), p. 615.
Individual evidence
- ↑ Entry on macrocycle . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.M03662 Version: 2.1.5.