Asymmetric carbon

Asymmetric carbon

An asymmetric carbon atom is a carbon atom that is attached to four different types of atom or four different groups of atoms.[1][2] Knowing the number of asymmetric carbon atoms, one can calculate the maximum possible number of stereoisomers for any given molecule as follows:

If n is the number of asymmetric carbon atoms then the maximum number of isomers = 2n

As an example, malic acid has 4 carbon atoms but just one of them is asymmetric:

example of an asymmetric carbon

A tetrose with 2 asymmetric carbon atoms has 22 = 4 stereoisomers:

4 asymmetric carbon atoms in an aldohexose

An aldopentose with 3 asymmetric carbon atoms has 23 = 8 stereoisomers:

4 asymmetric carbon atoms in an aldohexose

An aldohexose with 4 asymmetric carbon atoms has 24 = 16 stereoisomers:

4 asymmetric carbon atoms in an aldohexose

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.

References

  1. ^ Stereochemistry of Organic Compounds Ernest L. Eliel, Samuel H. Wilen
  2. ^ IUPAC definition http://goldbook.iupac.org/A00479.html

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