Stereoisomerism is a form of isomerism where molecules have the same molecular formula and the same connectivity of atoms (the same structural formula) but differ in the three-dimensional arrangement of their atoms in space. This difference can lead to varying physical and chemical properties among the isomers.
There are two main types of stereoisomerism:
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Geometric Isomerism (cis-trans isomerism): This occurs due to the restricted rotation around a double bond or within a ring structure, leading to isomers that differ in the spatial arrangement of groups. For example, in geometric isomers of alkenes, the cis form has similar groups on the same side of the double bond, while the trans form has them on opposite sides.
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Optical Isomerism (enantiomerism): This arises when molecules can exist as non-superimposable mirror images, much like left and right hands. These isomers are called enantiomers and often exhibit different optical activities, rotating plane-polarized light in different directions.
In summary, stereoisomerism accounts for the spatial orientation of atoms in a molecule, which can significantly impact its properties and reactivity.
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