31 Unit 3: Stereochemistry
Stereoisomersare isomers which have the same pattern of bonding but with atoms ar-
ranged differently in space. Stereoisomers are also known asgeometric 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 asoptical isomersdue
to the fact that two enantiomers will rotate plane-polarized light in equal, but opposite
directions.Chiralityis (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.