Before 1951 only relative configurations of chiral molecules were known. Configurations of chiral molecules were related to each other through reactions of known stereochemistry. The standard compound was glyceraldehyde
An equimolar mixture of two enantiomers is called a racemic form (either a racemate or a racemic mixture). A racemic form shows no rotation of planepolarized light
Isomers are different compounds that have the same molecular formula. Constitutional isomers are isomers that differ because their atoms are connected in a different order. Stereoisomers differ only in arrangement of their atoms in space.Stereoisomers are not constitutional isomers. Enantiomers are stereoisomers whose molecules are nonsuperposable mirror images of each other. Diastereomer are stereoisomers whose molecules are not mirror images of each other
