Stereochemistry is the study of organic compounds in space. To understand the properties of organic compounds it is necessary to consider all three spatial dimensions. 
The bases of stereochemistry were laid by Jacobus van't Hoff and Le Bel, in 1874. They independently proposed that the four substituents of a carbon are directed towards the vertices of a tetrahedron, with the carbon in the center of it. .
The tetrahedral arrangement of the substituents of an sp 3 carbon gives rise to the existence of two possible compounds, which are non-superimposable mirror images, called enantiomers.
In general, molecules that differ by the spatial arrangement of their atoms are called stereoisomers.
