calls Chiralität the Chiralität (Greek technical term, the handlingness, derived from the word trunk χειρ~, CH [e] ir~ - hand~) the characteristic of certain articles or systems that its mirror image cannot be set by turn with the original to the coincide.One calls objects with this characteristic thereby chiral, contrary to achiral.
General is an object exactly chiral if it does not possess a turning mirror axle. Other one Symmetry elements can be however quite available, i.e. a chirales object is not inevitably asymmetrical.
To table of contents
in chemistry designates Chiralität the spatial arrangement of atoms, with those determined symmetry operations, for example the reflection onone molecule level, not to a self illustration lead. Here can represent both particulars or several atoms in a molecule one or more stereogene centers and constitute the entire molecule shape the Chiralität.
Chiralität is usually based on the different spatial arrangement ofAtoms and atomic's groups over one or more Stereozentren. Thus z place. B. Carbon atoms with four different substituents a stereogenes center or Stereozentrum, with which two different spatial arrangements are possible. Also different atoms like for example phosphorus know Stereozentrentrain. Crucial it is here that the substituents cannot to each other change their relative situation.
Molecules, whose picture and mirror image cannot be set to the coincide, are called Enantiomere. The Enantiomere can be differentiated by its different optical activity. OneMixture with same portions of both Enantiomere is called Racemat or racemisches mixture.In the simplest case Chiralität is present in organic chemistry if in a molecule a carbon atom carries four different substituents. This carbon atom becomes as Stereozentrum (sometimes alsofalsely as Chiralitätszentrum or asymmetrical carbon atom) designates. The spatial arrangement of the substituents at a Stereozentrum becomes after by R. S. Cahn, C. K. Ingold and V. Prelog determined rules (CIP rules) with R or S (R forrectus, Latin “right”, and S for more sinister, lat. “designates left”). Forwards, also the number of possible different connections increases couches several Stereozentren. With n Stereozentren result 2 n different connections, less possible meso connections (see below). The Stereozentren becomes then in each caseindividually according to the CIP rules with R or S designates. If two connections differ in or several, not however in all Stereozentren, then one speaks of Diastereomeren. If a molecule exhibits several Stereozentren, it is in certain cases neverthelesspossible that the entire molecule achiral is. One speaks in this case of meso - connections (e.g. Meso tartaric acid).
Beside these Chiralität attributed to Stereozentren differentiates one axial, planar and helicale Chiralität, in order to describe the underlying structural components more near. Axial Chiralität e.g. steps. with Biphenylen up, so into thatOrtho positions are substituted that the free swivellingness that is reduced around the CC single bond aromatics. Examples of planar Chiralität are E - Cycloocten or certain sand yielding complexes. Helicale Chiralität e.g. steps. with Helicenen up.
Chiralität arises also in inorganic materials.Thus that possesses quartz two enantiomere forms, which can be attributed to left or right-handed screws. This is likewise an example of helicale Chiralität.
In crystallography the two forms are called chiral developed crystals enantiomorph.
The absolute configurationcan be deduced to a chiralen substance not from the direction of rotation of polarized light when passing a standard solution, but must either by chemical analogy reasoning (for example by dismantling of the substance which can be determined to a well-known connection), by Roentgen crystallography or by usechiraler SHIFT reagents in the NMR - spectroscopy take place. Only after such a proof, it can be decided whether a connection R - or S - possesses configuration. The allocation of the configurations for amino acids and coal hydrates, of those of beginning only the relativeConfigurations to each other admits were, took place first arbitrarily. (Into the 1950er years) X-ray-crystallographic investigations resulted in very many later that the selected allocation corresponds coincidentally to actual conditions.
the concept of the Chiralität plays also in biology,in particular in biochemistry, a fundamental role. Thus one finds a fundamental preference a Enantiomers in each case with the most important natural substance classes. There chirale (bio) molecules diastereoselektive reactions are received, continue this preference in entire biochemistry. Would be exactly taken from thisReason a “racemische biology” not at all possible. So z can. B. form only enantiomerenreine amino acids an arranged Helix. Racemi mixtures of chiraler molecules show therefore also usually different biological effects of the individual Enantiomere.*
also macroscopically are important chirale phenomena.The Chiralität of the hands and the freedom of movement of Schneckenhäusern was already mentioned. Further examples are the different function of the brain halves and the left-sided situation of the heart.
(*) In addition that this Racemisierung in biological systems does not exclude, see contergan Thalidomid.
with biocatalytic transformations is used that with conversions with enzymes as biocatalyst mostly a Enantiomer in the surplus develops, and/or if a Racemat is submitted as raw material, preferentially by the enzyme only a Enantiomer is converted. Correspond succeeds itTo receive products with so-called Enantiomerenüberschuss.