The key difference between stereocenter and chiral center is that a stereocenter is any point of a molecule that can give a stereoisomer when two groups are interchanged at this point whereas a chiral center is an atom in a molecule which can give an enantiomer when two groups at this center are interchanged.
The two terms stereocenter and chiral center are often used interchangeably because all chiral centers are stereocenters; however, all stereocenters are not chiral centers.
CONTENTS
1. Overview and Key Difference
2. What is a Stereocenter
3. What is a Chiral Center
4. Similarities Between Stereocenter and Chiral Center
5. Side by Side Comparison – Stereocenter vs Chiral Center in Tabular Form
6. Summary
What is a Stereocenter?
Stereocenter is a point in a molecule which can give rise to stereoisomers. However, it is not necessarily be an atom. If two groups of atoms bonded to this point are interchanged, it gives a stereoisomer. Stereoisomers are molecules that have the same molecular formula and atomic constitution, but different spatial arrangements.
Stereocenters are also known as stereogenic centers. If the stereocenter is a carbon atom, it can be either sp2 hybridized or sp3 hybridized. This means the stereocenter can have either double bonds or single bonds, respectively. Some achiral molecules also have stereocenters. For example, cis-trans isomers have stereocenters, but most of them have no chiral centers.
Figure 1: Cis-trans Isomers of Dichloroethene (I-cis isomer, II-trans isomer)
The above molecules have no chiral centers. But they have stereocenters. Both vinyl carbon atoms are stereocenters (double bonded carbon atoms). This is because when the groups attached to these carbon atoms interchange, they give rise to isomers.
What is Chiral Center?
Chiral center is a carbon atom to which four different atoms or groups of atoms are bonded. Chiral compounds are the compounds containing chiral carbon atoms. It is important to note that the property of having chiral centers is known as chirality. The chiral center is essentially sp3 hybridized because it has to bear four different groups of atoms, forming four single covalent bonds.
Figure 2: Enantiomers rise due to the presence of chiral centers.
Chiral centers cause the optical isomerism of compounds. In other words, compounds having chiral centers do not superimpose with its mirror image. Therefore, the compound having the chiral center and the molecule that resembles its mirror image are two different compounds. These two molecules together are known as enantiomers.
What are the Similarities Between Stereocenter and Chiral Center?
- Both stereocenters and chiral centers give rise to stereoisomers.
- All chiral centers are stereocenters, but all stereocenters are not chiral centers.
What is the Difference Between Stereocenter and Chiral Center?
Stereocenter vs Chiral Center |
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| Stereocenter is a point in a molecule which can give rise to stereoisomers. | Chiral center is a carbon atom to which four different atoms or groups of atoms are bonded. |
| Nature | |
| A stereocenter is a point in a molecule, not necessarily an atom. | A chiral center is a carbon atom. |
| Hybridization of carbon | |
| If stereocenter is a carbon atom, it can be either sp2 hybridized or sp3 hybridized. | Chiral centers are essentially sp3 hybridized. |
| Groups of Atoms | |
| Stereocenters can have either three or four groups attached to it. | Chiral centers essentially have four groups attached to it. |
| Chemical Bonds | |
| Stereocenter can have either single bonds or double bonds around it. | Chiral centers have only single bonds around it. |
| Results of Interchanging Groups | |
| The interchange of groups at the stereocenter forms stereoisomers. | The interchange of groups at the chiral center forms enantiomers. |
Summary – Stereocenter vs Chiral Center
All chiral centers are stereocenters, but all stereocenters are not chiral centers. A stereocenter is any point of a molecule which can give a stereoisomer when two groups are interchanged at this point whereas a chiral center is an atom in a molecule which can give an enantiomer when two groups at this center are interchanged. This is the key difference between stereocenter and chiral center.
Image Courtesy:
1. “Dichloroethene” By V8rik – en:Image:Dichloroethene.png (CC BY-SA 3.0) via Commons Wikimedia
2. “Thalidomide-enantiomers” By Klaus Hoffmeier – Own work (Public Domain) via Commons Wikimedia
Reference:
1. Helmenstine, Anne Marie. “What Is a Chiral Center in Chemistry?” ThoughtCo, Available here.
2. “Chirality (Chemistry).” Wikipedia, Wikimedia Foundation, 10 Apr. 2018, Available here.
3. “Stereocenter.” Wikipedia, Wikimedia Foundation, 10 Apr. 2018, Available here.