Diastereomers

Diastereomers are compounds that have the same chemical formula and bound element sequence but are not superimposable or mirror copies.

Stereoisomers are enantiomers and diastereomers that fall under the broader idea of isomerism, which always includes the comparison of at least two species.

Stereoisomers are molecules that have the same structure but are not the same. Diastereomer differences can be described in scalar terms, that is, by differences in the distances between certain typical pairs of atoms.

Explanation of Diastereomers

Diastereomers are stereoisomers that are not associated as an object and its mirror image; Diastereomers are stereoisomers that are not mirror images.

Consider the formula for 2,3-dichloropentane, which has two chiral centres. Now contrast the two forms of 2,3-dichloropentane shown below.

It is instantly obvious that the two equations contain identical configurations around one chiral carbon C2 and mirror image configurations around the other chiral carbon (C3). As a result, the two forms are neither identical nor mirror reflections of one another. Diastereomers are stereoisomers of a material that are not mirror images of each other.

Another example of a molecule with two different chiral carbon atoms is 3-chloro-2-butanol, which can exist in four stereoisomeric forms, as shown below.

It may be seen that structures 1 and 3, 1 and 4, 2 and 3, 2 and 4 represent pairs of diastereomers.

Diastereomer Characteristics

• Melting and boiling temperatures, densities, solubilities, refractive indices, dielectric constants, and specific rotations are all physical properties of diastereomers. Enantiomers have similar physical properties with the exception of the opposite sign of specific rotation.

• Diastereomers, unlike geometrical isomers, may or may not be optically active. 

• Diastereomers have chemical properties that are similar but not identical. The reaction rates of the two diastereomers with a certain reagent, provided that the reagent is not rapidly active.

• Diastereomers can be separated from one another based on physical property changes utilising techniques such as fractional crystallisation, fractional distillation, chromatography, and so on. The separation of enantiomers that cannot be differentiated using standard methods.

Diastereomers of Erythro and Threo

Diastereomers are stereoisomers which are not mirror images.. They are geometrical isomers or compounds with two or more chiral centres. Erythro occurs when the Fischer projection of a diastereomer shows similar groups on the same side of the molecule. It is referred to as threo when similar groupings are on opposing sides of the Fischers projection.

The hydroxylation of trans-crotonic acid produces two enantiomers of threo-2,3-dihydroxybutanoic acid, whereas the hydroxylation of cis-crotonic acid produces erythro enantiomers.

Each threo isomer is a diastereomer of each erythro isomer. The words erythro and threo are normally reserved for molecules having asymmetric ends.

Properties of Enantiomers and Diastereomers

Except for their optical rotation, enantiomers have identical chemical and physical properties. When compared, diastereomers have differing physical qualities and, in some cases, chemical features as well. The properties of enantiomers and diastereomers are compared and contrasted in the table below.

The characteristics of enantiomers and diastereomers are compared.

CONCLUSION

Diastereomers are defined as non-mirror image non-identical stereoisomers that are not mirror images of each other. In other words, they occur when two or more stereoisomers of the same compound have different configurations at one or more (but not all) of the equivalent (related) stereocenters and are not mirror images of one another. [2] They are called epimers when two diastereoisomers differ from each other at only one stereocenter. Each stereocenter gives rise to two different configurations, resulting in a typical increase in the number of stereoisomers by a factor of two for each centre.