Changes at "Frequently Asked Questions about Chemical Chirality"
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- What is chemical chirality?
Chirality refers to the property that the left hand and the right hand are mirror images of each other and cannot overlap. Molecules that perfectly coincide with their mirror images are called achiral molecules, while those that do not perfectly coincide with their mirror images are called chiral molecules.
The ability of chiral compounds to deflect the plane of polarized light is called optical activity. A mixture of equal amounts of the dextrorotatory and levorotatory enantiomers does not exhibit optical activity and is called a racemic mixture or racemate.
The vast majority of chiral compounds contain one or more chiral carbon centers in a tetrahedral configuration. Most of the asymmetry is formed when sp2-hybridized carbon atoms are converted to sp3-hybridized atoms. For example, carbonyl groups, enamines, imines, and alkenes undergo chemical reactions that may introduce chiral carbon atoms into the molecule.
Enantiomers are a pair of molecules that exist in two forms that are mirror images of each other but cannot be superimposed on each other. Diastereomers are defined as non-mirror-image compounds that have the same molecular formula and order of bonding elements but are not superimposable.
Chiral catalysis can be represented in a general picture as a process that takes place in a so-called chiral pocket formed by the catalytic centre (in many cases a metal) and the bulky groups in the near environment that restrict the mobility of molecules around the coordinated substrate, provoking the enantioselection. Chiral catalysis can be divided into chiral metal catalysis, organic small molecule catalysis and biocatalysis.
A chiral auxiliary is a compound or unit temporarily added to an organic synthesis reaction in order to control the stereochemical outcome of the synthesis. Chiral auxiliaries can bias the stereoselectivity of one or more subsequent reactions.
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