Isomers which have the same molecular formula and same structure but differ in the arrangement of atoms or groups in space. There are two types of stereoisomerism.
- Geometric isomerism
- Optical isomerism.
Isomers which arise due to the different spatial arrangement of atoms or groups around double bond or in cyclic compounds. In organic chemistry geometric isomerism otherwise known as cis/trans isomerism. Generally such isomers contain double bond , which cannot rorate, and also one form cannot be readily converted into the other form without breakage of a bond. cis and trans isomers occur both organic molecule and inorganic coordination complexes.
The identical groups lying on the same side, the diastereomers is referred to as cis. In Latin cis means ' on the same side '
The identical groups lying on the opposite side, the diastereomers is referred to as trans. In Latin trans means ' across ' or 'on the other side'.
Disubstituted cyclic compounds can also exist in two different forms.
In coordination complexes cis isomers in which similar ligands are closer together and trans isomers in which similar ligands are opposite together. Not all coordination compounds have geometric isomers.
Two isomers of squar planar Pt(NH3)Cl2.
Cis isomer used in anti-tumor activity.
Trans isomer does not exhibit any anti-tumor activity.