•Stereoisomers- isomers in which the atoms in two molecules are connected in the same order, but have different arrangements in space.
Ie. Rotation through bonds.
There are 2 types of stereoisomers:
Optical isomers- stereoisomers in which there is a different placement of groups around one atom in the molecule.
Called optical isomers because of the way they interact with plane-polarised light.
Substances that are optical isomers are said to be chiral- mirror images of each other.
Eg. Methane- where carbon is the chiral centre.
A pair of chiral molecules are called enantiomers.
Properties of enantiomers
Identical physical properties- except with plane-polarised light.
Interact differently with other chiral molecules.
Geometric isomers- these isomers occur when there is restricted rotation somewhere in a molecule.eg. Carbon carbon double bond.
Cis- groups appear on the same side of the double bond.
Trans-groups appear on different sides of the double bond.
Images of cis and trans-1,4-Dichloro-2-butene
Images created using Molview
Optical isomerism diagram By Internet Archive Book Images [No restrictions], via Wikimedia Commons
Dinitrogen diflouride cis and trans molecules diagrams By R8R Gtrs (Own work) [CC0], via Wikimedia Commons