Definition of Isomer
Isomers are molecules that have the same molecular formula but different structures. They are classified into structural isomers and stereoisomers.
Structural Isomers
Structural isomers differ in the way atoms are connected and are further classified into chain, position, and functional isomers.
Stereoisomers
Stereoisomers have identical bonds but differ in the spatial arrangement of groups. They are classified into cis-trans or geometric isomers, enantiomers, and diastereoisomers.
Chiral or Asymmetric Center
A chiral or asymmetric center refers to an atom bonded to four different substituents. A molecule possessing a chiral center has a non-superimposable mirror image, called an enantiomer.
Optical Activity
Enantiomers possess almost identical physical properties, except for optical activity. One of the enantiomers rotates polarized light to the right (dextrorotatory) and the other rotates polarized light to the left (levorotatory).
Stereochemistry in Reactions
Radical halogenation reactions on molecules where chiral centers can be formed produce mixtures of enantiomers in equal quantity or of diastereoisomers in different proportions.
Separation of Enantiomers
Enantiomers have almost all physical properties the same, they differ in polarized light rotation, but have the same melting and boiling points and identical solubility. Therefore, traditional separation methods cannot be applied, and special techniques must be used. Separation via diastereoisomers involves transforming the mixture of enantiomers into a mixture of diastereoisomers by adding a chiral reagent, which are easily separable by physical methods.