Isomer definition

Molecules that have the same molecular formula but different structures are called isomers. It is classified as structural isomers and stereoisomers.

Structural isomers

Structural isomers differ in the way the atoms are joined and are in turn classified into positional and functional chain isomers.

Stereoisomers

Stereoisomers have all the identical bonds and are differentiated by the spatial arrangement of the groups. They are classified as cis-trans or geometric isomers, enantiomers and diastereoisomers.

Chiral or asymmetric center

An atom bonded to four different substituents is called a chiral or asymmetric center. A molecule that has a chiral center has a non-superimposable mirror image of it, called an enantiomer.

Optical activity

The enantiomers have almost all identical physical properties, with the exception of optical activity. One of the enantiomers rotates polarized light to the right (right-handed) and the other rotates polarized light to the left (left-handed).

Stereochemistry in reactions

Radical halogenation reactions on molecules in which chiral centers can be formed produce mixtures of enantiomers in equal amounts or of diastereoisomers in different proportions.

Separation of enantiomers

Enantiomers have almost all the same physical properties, differ in rotation polarized light, but have the same melting and boiling points and identical solubility. Therefore, we cannot apply the traditional methods of separation and we must resort to special techniques. The separation via diastereoisomers, consists of transforming the mixture of enantiomers into a mixture of diastereoisomers by adding a chiral reagent, the diastereoisomers are easily separated by physical methods.