An asymmetric carbon atom (chiral carbon) is a

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, and ...

that is attached to four different types of atoms or groups of atoms. Le Bel-van't Hoff rule states that the number of stereoisomers of an organic compound is 2ⁿ, where n represents the number of asymmetric carbon atoms (unless there is an internal plane of symmetry); a corollary of Le Bel and van't Hoff's simultaneously announced conclusions, in 1874, that the most probable orientation of the bonds of a carbon atom linked to four groups or atoms is toward the apexes of a tetrahedron, and that this accounted for all then-known phenomena of molecular asymmetry (which involved a carbon atom bearing four different atoms or groups). Knowing the number of asymmetric carbon atoms, one can calculate the maximum possible number of

stereoisomers In stereochemistry, stereoisomerism, or spatial isomerism, is a form of isomerism in which molecules have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in ...

for any given molecule as follows: : If n is the number of asymmetric carbon atoms then the maximum number of isomers = 2ⁿ ( Le Bel-van't Hoff rule) As an example,

malic acid Malic acid is an organic compound with the molecular formula . It is a dicarboxylic acid that is made by all living organisms, contributes to the sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms ...

has 4 carbon atoms but just one of them is asymmetric. The asymmetric carbon atom is the one attached to two carbon atoms, an oxygen atom, and a hydrogen atom. One may initially be inclined to think this atom is not asymmetric because it is attached to two carbon atoms, but because those two carbon atoms are not attached to exactly the same things, there are two different ''groups'' of atoms that the carbon atom in question is attached to, therefore making it an asymmetric carbon atom: : Äpfelsäure3

tetrose A tetrose is a monosaccharide with 4 carbon atoms. They have either an aldehyde functional group in position 1 (aldotetroses) or a ketone functional group in position 2 (ketotetroses). File:DErythrose Fischer.svg , D-Erythrose File:DThreose Fisch ...

with 2 asymmetric carbon atoms has 2² = 4 stereoisomers: : Tetrose

aldopentose In chemistry, a pentose is a monosaccharide (simple sugar) with five carbon atoms. The chemical formula of many pentoses is , and their molecular weight is 150.13 g/mol. An aldohexose with 4 asymmetric carbon atoms has 2⁴ = 16 stereoisomers: : Aldolhexose

The four groups of atoms attached to the carbon atom can be arranged in space in two different ways that are mirror images of each other, and which lead to so-called left-handed and right-handed versions of the same molecule. Molecules that cannot be superimposed on their own mirror image are said to be

chiral Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from ...

like mirror image.

References

{{DEFAULTSORT:Asymmetric Carbon Stereochemistry Jacobus Henricus van 't Hoff de:Asymmetrisches Kohlenstoffatom