Enantiomers are a pair of molecules that exist in two forms that can not be superimposed on each other but are mirror images of each other.
Enantiomers have a chiral carbon. A chiral carbon is a center of carbon that is bound to four distinct atoms or groups. The existence of a chiral carbon is referred to as chirality (in a molecule). Two molecules in each chiral carbon should have different configurations in order to become an enantiomer. For example, if a molecule has two chiral carbons and another molecule has two chiral carbons in the same molecular formula, the two molecules for both chiral carbons, not just one chiral carbon, should be different.
We discussed the enantiomer’s definition, now let’s study the chirality and properties of enantiomers.
It is also important to remember that more than one chiral characteristic is possible for a molecule. These molecules have many geometric shapes that are considered to have (however, some of these forms may still be perfect mirror images of each other). It should also be noted that the physical and chemical properties of the two enantiomers are almost identical when the enantiomers are put in a symmetrical setting. They vary, however, in the directions in which polarised light is rotated by the plane. For instance, if one enantiomer rotates the polarised light plane to the left, the other enantiomer rotates the polarised light plane to the right.
Enantiomers are chemically similar in any other respect. A pair of enantiomers is characterized by the direction in which polarised light is rotated. It can be dextrorotatory or laevorotatory, hence the term optical isomers are used. If two enantiomers are similarly present, they are collectively referred to as a racemic mixture, a mixture that does not rotate polarized light because the other cancels the optical behavior of each enantiomer.
Properties of Enantiomers
Enantiomers generally have identical physical properties such as melting point, boiling point, infrared absorptions, and NMR spectra.
It is important to realize that the melting point of one enantiomer will be identical to that of the other enantiomer, the melting point of a mixture of the two enantiomers may be different.
This is because the intermolecular interactions between opposite enantiomers that are between the R and S enantiomers may be -different from those between like enantiomers that are between two molecules both of R or both of S stereochemistry.
Structure of Enantiomers
As stereoisomers that are non-superimposable mirror images of one another, enantiomers were introduced.
Any molecule which is not superimposed on its mirror image and thus exists is said to be chiral and to show chirality as a pair of enantiomers. In comparison, any molecule which can be superimposed over its mirror image is achiral.
Indeed, it is possible to have two enantiomers if a molecule contains a single atom that is tetrahedrally bound to four separate substituents.
It is important, however, that the four substituents differ from each other as if two of them were the same, then the structure would become superimposed on its mirror image and thus achiral. It is better to refer to the atom linked to four distinct atoms as a stereogenic core or simply a stereocenter.
A commonly used alternate name for a stereocenter, although somewhat misleading, is located around the central atom, whereas chirality is a property of the molecule as a whole that can not be located around one atom or a group of atoms.
Chemical Nature of Enantiomers
It is understood that chemical compounds exhibiting stereoisomerism and having different enantiomeric structures frequently take part in chemical reactions with other enantiomeric compounds. Currently, enantiomers are considered to be certain biological molecules. In addition, it is important to remember that two different enantiomers of the same chemical compound can affect many species in a completely different way. This phenomenon is commonly found in the effects on human beings of various medicines. In certain cases, only one of a drug's enantiomers would be able to bring about the physiological improvements that are needed.
Did You Know?
Stereoisomers are classified into diastereoisomers and enantiomers. The difference between the two is given below.