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Introduction to Stereochemistry

Stereochemistry is a branch of organic chemistry that focuses on the disposition in space, or spatial arrangement, of molecules, and the main subjects of study are the different isomers of molecules. An isomer is a chemical compound that has the same molecular formula as another, but a different arrangement of atoms in space. Recognizing the difference between isomers is fundamental not only for classification but also because they can differ in chemical and biological properties. Isomers can be divided between constitutional isomers and stereoisomers:

  • Constitutional isomers have the same atoms (molecular formula) but the bonds that connect them are different.
  • Stereoisomers, or spatial isomers, share the same atoms and bonds but are arranged differently in space. These molecules are defined as chiral.

Stereoisomers can be divided further into two other categories: enantiomers and diastereomers.

A tree diagram demonstrating the different forms of isomers. At the top of the tree is a box labeled isomers, this is connected to a box titled constitutional structural isomers and another titled stereoisomers spatial isomers. The stereoisomers have two sub-categories: diastereomers and enantiomers. Diastereomers are split into cis-trans isomers and conformers. Finally, under conformers is a box labeled rotamers.

Figure 1: Stereochemistry scheme.