Organic Chemistry/Stereochemistry

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Organic Chemistry table of contents > Stereochemistry

Stereoisomers are isomers which have the same pattern of bonding but with atoms arranged differently in space. Stereoisomers are also known as geometric isomers but confusingly this latter term is often used to refer only to 'cis/trans isomers'.

There are two types of stereoisomer:

Enantiomers: two isomers which are mirror images of each other; also known as optical isomers due to the fact that two enantiomers will rotate plane-polarized light in equal, but opposite directions. Chirality is (yet) another term for enantiomerism.

Diastereomers: stereoisomers which are not enantiomers.

Stereoisomerism can be caused by:

Stereocenters: if a carbon atom has four different groups attached to it, it will exhibit enantiomerism. Other causes of enantiomerism include helical structures.

Non-rotation of bonds: the C=C bond cannot rotate and is the most common cause of diastereomerism. Other causes are cyclic compounds and steric hindrance.