Two enantiomers are chemically identical because they are mirror images of one another. Other types of stereoisomers may be chemically (and physically) quite different. These two alkenes, for example, are geometrical isomers (or cis–trans isomers). Their physical chemical properties are different, as you would expect, since they are quite different in shape. Neither is chiral of course as they are planar molecules.

A similar type of stereoisomerism can exist in cyclic compounds. In one of these, 4-t-butyl cyclohexanols, the two substituents are on the same side of the ring; in the other, they are on opposite sides of the ring. Again, the two compounds have chemical and physical properties that are quite different.

Stereoisomers that are not mirror images of one another are called diastereoisomers. Both of these pairs of isomers fall into this category. Notice how the physical and chemical properties of a pair of diastereoisomers differ.

● The physical and chemical properties of enantiomers are identical; the physical and chemical properties of diastereoisomers differ. ‘Diastereoisomer’ is sometimes shortened to ‘diastereomer’.

مواضيع ذات صلة

Significance of the SN2 rate equation

Mechanisms for nucleophilic substitution

Resolutions using diastereoisomeric salts

Separating enantiomers is called resolution

Chiral compounds with no stereogenic centres

Diastereoisomers can arise when structures have more than one stereogenic centre

Absolute and relative stereochemistry

Diastereoisomers can be chiral or achiral

The rotation of plane-polarized light is known as optical activity

R and S can be used to describe the configuration of a chiral centre

Many chiral molecules are present in nature as single enantiomers

Stereogenic centres