The key difference between enantiotopic and diastereotopic is that the term enantiotopic refers to the ability to form a chiral centre, whereas the term diastereotopic refers to the ability to form a diastereomer.
Topicity in chemistry is the stereochemical relationship between substituents and the parent structure to which these substituents are attached. There are different types of topicity depending on the relationship such as heterotopic, homotopic, enantiotopic, and diastereotopic.
CONTENTS
1. Overview and Key Difference
2. What is Enantiotopic
3. What is Diastereotopic
4. Side by Side Comparison – Enantiotopic vs Diastereotopic in Tabular Form
5. Summary
What is Enantiotopic?
Enantiotopic is a term that describes a phenomenon where two substituents in a molecule are replaced by some other atoms, forming a chiral compound. Therefore, it is a stereochemical term. The replacement that can occur in this type of reactants can form enantiomers. Let us consider an example in order to understand the meaning of this term.
Butane molecule has two hydrogen atoms attached to each of the second and third carbon atoms. If we consider one carbon atom, say the second carbon atom, there are two hydrogen atoms attached to this carbon centre, and we can replace one of these hydrogen atoms with some other atom such as bromine, that can generate enantiomers, e.g. (R)-2-bromobutane. Similarly, the replacement of the other hydrogen atom with bromine will give the enantiomer of (R)-2-bromobutane, which is (S)-2-bromobutane. The structures are as follows:
Figure 01: Structure of Butane
Figure 02: Structure of (R)-2-bromobutane
Figure 03: Structure of (S)-2-bromobutane
Usually, the enantiotopic substituent groups are identical and indistinguishable from each other, except in chiral compounds. For example, normally the hydrogen atoms in the middle carbon of ethanol molecule (CH3CH2OH) are enantiotopic, but these can become diastereotopic if the molecule is combined with a chiral centre (e.g. conversion into an ester).
What is Diastereotopic?
Diastereotopic is a term that describes a phenomenon where two substituents in a molecule are replaced by some other atoms, forming diastereomers. Therefore, this is a stereochemical term. Diastereotopic substituent groups are often identical but not always. Moreover, these identical groups are usually attached to the same atom of the molecule having at least one chiral centre. For instance, in the structure for (S)-2-bromobutane above, the hydrogen atoms in the third carbon atom are diastereotopic.
Figure 04: Structure of (2S,3R)-2,3-dibromobutane
Figure 05: Structure of (2S,3S)-2,3-dibromobutane
The above diagrams indicate the replacement of one of these hydrogen atoms with another atom such as a bromine atom can form (2S,3R)-2,3-dibromobutane and the replacement of the other hydrogen atom with a bromine atom forms the diastereomer of (2S,3R)-2,3-dibromobutane, which is (2S,3S)-2,3-dibromobutane.
What is the Difference Between Enantiotopic and Diastereotopic?
Enantiotopic and diastereotopic are two types of topicity in chemical compounds. These two types of topicity differ from each other according to the final product they give when atoms are replaced with some other atoms. The key difference between enantiotopic and diastereotopic is that the term enantiotopic refers to the ability to form a chiral centre, whereas the term diastereotopic refers to the ability to form a diastereomer.
Below infographic shows more details of the difference between enantiotopic and diastereotopic.
Summary – Enantiotopic vs Diastereotopic
Enantiotopic and diastereotopic are two types of topicity in chemical compounds. The key difference between enantiotopic and diastereotopic is that the term enantiotopic refers to the ability to form a chiral centre whereas the term diastereotopic refers to the ability to form a diastereomer.
Reference:
1. “Homotopic Enantiotopic Diastereotopic and Heterotopic.” Chemistrysteps, Available here.
Image Courtesy:
1. “Enantiotopic1” By Edgar181 – Own work (Public Domain) via Commons Wikimedia
2. “Enantiotopic3” By Edgar181 – Own work (Public Domain) via Commons Wikimedia
3. “Enantiotopic2” By Edgar181 – Own work (Public Domain) via Commons Wikimedia
4. “Diastereotopic3” By Edgar181 – Own work, Public Domain) via Commons Wikimedia
5. “Diastereotopic2” By Edgar181 – Own work, Public Domain) via Commons Wikimedia