What is the Difference Between Prochirality and Prostereoisomerism

The key difference between prochirality and prostereoisomerism is that in prochirality, the prochiral center may be a prostereogenic centre whereas, in prostereoisomerism, prostereogenic center may not be necessarily a prochiral center.

Prochirality and prostereoisomerism are two chemical concepts in organic chemistry that refer to the conversion between similar chemical structures. Prochirality refers to the ability of the molecules that can be converted from achiral to chiral molecules in a single step. Prostereoisomerism refers to the ability of some molecules to be converted into their stereoisomeric forms. The stereoisomeric forms are either enantiomers or diastereomers.

CONTENTS

1. Overview and Key Difference
2. What is Prochirality
3. What is Prostereoisomerism
4. Prochirality vs Prostereoisomerism in Tabular Form
5. Summary – Prochirality vs Prostereoisomerism

What is Prochirality?

Prochiral molecules are molecules that can be converted from achiral to chiral in a single step. Therefore, prochirality refers to the property of an achiral molecule that is capable of turning chiral in a single step. Proprochirality, on the other hand, is the ability to convert an achiral species into a chiral in species in two steps.

If there are two identical substituents that are attached to an sp3 hybridized atom, we can use pro-R and pro-S as the descriptors to distinguish between the two forms. When naming a molecule, we have to give higher priority to the pro-R form compared to the other form with the identical substituent. This creates an R chirality center at the sp3 hybridized atom, and this form is analogous to the pro-S form.

When considering the sp2 hybridized atom having a trigonal planar, we can convert it into a chiral center upon addition of a substituent to the “re” or “si” ace of the molecule as shown below in the image.

We can name the face as “re” if the substituents at the trigonal atom appear in decreasing Cahn-Ingold-Prelog priority order. This order should be in a clockwise direction. Moreover, we can name the face as “si” when the priority tends to decrease in the counterclockwise direction. Furthermore, the chiral center is known as S or R, depending on the priority of the incoming group.

It is necessary to understand the concept of priority in order to understand some aspects of enzyme stereospecificity.

What is Prostereoisomerism?

Prostereoisomerism refers to the ability of some molecules to be converted into their stereoisomeric forms. The stereoisomeric forms are either enantiomers or diastereomers. For example, C molecules are achiral, but if we substitute Hydrogen atoms one by one with non-equivalent ligands, we can get a chiral molecule after three such substitutions because the carbon center then becomes stereogenic. Prostereoisomerism represents a subgroup within the achiral class of molecules which is manifested in a chiral environment.

What is the Difference Between Prochirality and Prostereoisomerism?

Prochirality and prostereoisomerism are two chemical concepts in organic chemistry and refer to the conversion between similar chemical structures. The key difference between prochirality and prostereoisomerism is that in prochirality, the prochiral center may be a prostereogenic center whereas, in prostereoisomerism, prostereogenic center may not be necessarily a prochiral center.

The following table summarizes the difference between prochirality and prostereoisomerism.

Summary – Prochirality vs Prostereoisomerism

Prochirality and prostereoisomerism are two chemical concepts in organic chemistry that refer to the conversion between similar chemical structures. The key difference between prochirality and prostereoisomerism is that in prochirality, the prochiral center may be a prostereogenic center whereas in prostereoisomerism, prostereogenic center may not be necessarily a prochiral center.

Reference:

1. “5.11: Prochirality.” Chemistry LibreTexts, Libretexts, 16 Sept. 2021.

Image Courtesy:

1. “Prochirality V.1” By Jü – Own work (Public Domain) via Commons Wikimedia