Easy Ways to Memorize the Difference Between Enantiomers and Diastereomers

Difference-Between-Enantiomers-and-Diastereomers

Stereoisomerism and Stereochemistry

Stereochemistry is defined as the “examination of multiple spatial arrangements of atoms contained in molecules” in the field of chemistry.

Stereochemistry is the systematic presentation of a particular branch of science and technology, which generally demands a slight detour into history. 

Stereochemistry is also known as’ space chemistry’ because it deals with the spatial configurations of groups and atoms in a molecule.

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Stereoisomerism is defined as “the isomerism generated by non-similar configurations of functional groups or atoms in space that belong to an atom.” These isomers have similar constitutions but different geometric arrangements of atoms. Stereoisomers are divided into enantiomers and diastereomers. 

In this article, we will Distinguish Between Enantiomers and Diastereomers.

Enantiomers

Enantiomers are chiral compounds that are mirror images of one another and cannot be superimposed. Diastereomers are stereomer compounds that contain molecules that do not mirror one another and cannot be superimposable. 

They are mirror images of each other that cannot be superimposed. This means they are mirror pictures of each other, but they cannot be stacked on top of each other and line up the same.

The enantiomers D and L relate to the configurational stereochemistry of the molecule. The hydroxyl group in L isomers is located on the far left side of the asymmetric carbonyl carbon. In contrast, the hydroxyl group in D isomers is situated on the far right side.

Properties

  • Physical parameters such as melting temperature, boiling point, infrared absorptions, and NMR spectra are generally equal amongst enantiomers.
  • However, the melting point and other properties of one enantiomer will be equal to those of the other enantiomer. The melting point of a mixture of the two enantiomers may differ.
  • This is because the intermolecular interactions between opposed enantiomers that are between the R and S enantiomers may differ from those between similar enantiomers that are between two molecules that are both R or both S stereochemistry.
  • Chiroptical techniques, the most prominent of which is optical rotation, are the only type of physical approach that can discriminate between two enantiomers of a chemical.
  • The chiroptical properties of a molecule are dictated by bond lengths and angles and the sign and magnitude of the torsional angles. The only difference between enantiomers is the sign of the torsional angles.

Structure

  • Enantiomers are the kind of stereoisomers that are not superimposable mirror images of one another.
  • A molecule that is not superimposable on its mirror counterpart and hence exists as a pair of enantiomers is said to be chiral. 
  • In contrast, any molecule that can be superimposed on its mirror copy is achiral.
  • Indeed, two enantiomers are feasible if a molecule comprises a single atom tetrahedrally bonded to four distinct substituents.
  • However, the four substituents must be distinct because if any two of them are identical, the structure becomes superimposable on its mirror image and hence achiral. 
  • A stereogenic centre, or simply a stereocenter, is an atom related to four distinct atoms.
  • A stereocenter is a molecule’s property as a whole that cannot be localized around one atom or a group of atoms. In contrast, chirality is a feature of the molecule as a whole that cannot be localized around one atom or a group of atoms.
  • The presence of a stereocenter is not required for a molecule to be chiral; instead, it is the most prevalent source of chirality.

Diastereomers

Diastereomers are compounds with the same chemical formula but are not superimposable or mirror copies. Diastereomers are stereoisomers compounds that contain molecules that do not mirror reflections of one another and cannot be superimposed. When you look at the cis and trans isomer structure, you can see an excellent example of diastereomers.

Diastereomers frequently contain molecules with ring structures. Consider two compounds with a six-membered ring, two substituents, an ethyl group, and a chlorine atom. They have not mirrored images as in the previous example, defining them as diastereomers.

Properties

  • Different physical properties of diastereomers include melting and boiling temperatures, densities, solubilities, refractive indices, dielectric constants, and specific rotations. 
  • Except for the opposite sign of specific rotation, enantiomers have similar physical characteristics.
  • Other than geometrical isomers, diastereomers may or may not be optically active.
  • Diastereomers have chemical characteristics that are similar but not identical. The two diastereomers’ reaction rates with a given reagent, assuming that the reagent is not rapidly active.

Diastereomers of Erythro and Threo

Stereoisomers that do not mirror images are referred to as Diastereomers. They are geometrical isomers or compounds with two or more chiral centers. If the Fischer projection of a diastereomer exhibits comparable groups on the same side of the molecule, it is termed erythro. If similar groupings are on opposing sides of the Fischer projection, it is called threo.

Trans-crotonic acid hydroxylation yields two enantiomers of threo-2,3-dihydroxybutanoic acid, whereas cis-crotonic acid hydroxylation yields erythro enantiomers.

Difference Between Enantiomers And Diastereomers

  • Enantiomers are mirror representations of each other that cannot be superimposed. Stereoisomers are enantiomers that are mirror images of each other.

Diastereomers are non-superimposable as well, although they do not mirror reflections of each other. Diastereomers are not reflected pictures of each other, as stereoisomers are.

  • The physical and chemical features of diastereomers vary. 

Except for interactions with eight and other chiral substances, all enantiomers have identical physical and chemical characteristics.

  • One or more stereocenters exist in enantiomers.

Diastereomers have at least two stereocenters.

  • All enantiomers pass optical activity. They have equal but opposing rotational angles.

Diastereomers do not all pass the optical activity. They do not rotate at the same angle.

  • The shapes of molecules in enantiomers are similar.

Diastereomers have a variety of molecular shapes.

  • Enantiomers exist in pairs.

Diastereomers can contain several molecules.

Stereoisomers are optically active among structural isomers and stereoisomers due to the presence of chiral centers. The main distinction between diastereomers and enantiomers is that the former is not a mirror image, whereas the latter is. So in this article, we wrote about the differences between enantiomers and diastereomers.

Conclusion

Read more articles to understand the difference between enantiomers and diastereomers in depth. The science of chemistry is intricate where the characteristics of every compound differ. Ensure you have your facts in check. 

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