Topomerization
Topomerization (from the Greek topos, place, and meros, proportion) describes a special case of isomerization with a change of place of normally indistinguishable components of the molecule . The associated isomers are called topomers .
An example is the chair conformation of cyclohexane (see conformation ), pyramidal inversion or pseudorotations . However, constitutional isomerism can also be present, but with identical components of the molecule. But they can sometimes be distinguished by dynamic NMR . One example is naphthalene with thermal change of the carbon atoms in positions 1 and 2, which can be detected when labeling with isotopes is used (this case was also called automerization ).
A third possibility is valence isomerizations in rapidly fluctuating compounds in the molecule, for example the Cope rearrangement in Bullvalen .
In the past, the terms isodynamic exchange and degenerate isomerization were also used . The name topomerization was proposed by Gerhard Binsch , Ernest Eliel, and Horst Kessler in 1971 ( We propose that the process leading to the exchange of the positions of identical ligands be called "topomerization" ). The starting point was the proposal to designate chemical ligands in stereochemically different environments as heterotopic and in identical environments as homotopic .
It is to be distinguished from topological isomerism .
swell
- Stefan Kubik: Entry on topomerization. In: Römpp Online . Georg Thieme Verlag, accessed on March 28, 2019.
Individual evidence
- ↑ Binsch, Eliel, Kessler, A Nomenclature for Intramolecular Exchange Processes , Angewandte, Chemie, Volume 83, 1971, p. 618. At the same time, they suggested the term topomer.