What is the Difference Between Anomeric Carbon and Chiral Carbon

The key difference between anomeric carbon and chiral carbon is that an anomeric carbon atom essentially contains a hydroxyl group that is either cis or trans to the exocyclic oxygen atom, whereas a chiral carbon atom essentially contains four different functional groups attached to it with single covalent bonds.

Anomeric carbon is the carbon originated from the carbonyl carbon compound of the open-chain form of the carbohydrate molecule. Chiral carbon atoms are carbon atoms consisting of four single bonds to four different functional groups.

CONTENTS

1. Overview and Key Difference
2. What is Anomeric Carbon 
3. What is Chiral Carbon 
4. Anomeric Carbon vs Chiral Carbon in Tabular Form
5. Summary – Anomeric Carbon vs Chiral Carbon

What is Anomeric Carbon?

Anomeric carbon is the carbon derived from the carbonyl carbon compound of the open-chain form of the carbohydrate molecule. According to the chemical structure of anomeric carbon-containing compounds, there are two types as alpha anomers and beta anomers.

Alpha anomer is the configuration of a carbohydrate in which the hydroxyl group is cis to the exocyclic oxygen at the anomeric centre. That means the hydroxyl group and the exocyclic oxygen atom are on the same side of the molecular projection. When we draw a Haworth formula, the hydroxyl group is in the downward direction if it is the alpha anomer. The following example shows the alpha anomer of D-glucopyranose.

Beta anomer is the configuration of a carbohydrate in which the hydroxyl group is trans to the exocyclic oxygen at the anomeric centre. That means the hydroxyl group and the exocyclic oxygen atom are on the opposite sides of the molecular projection.

What is Chiral Carbon?

Chiral carbon atoms are carbon atoms consisting of four single bonds to four different functional groups. The concept of the presence of a chiral carbon is best described by chirality. Chirality refers to the property of having a superposable mirror image. This term is mostly used with organic compounds. The point that determines the presence or absence of chirality in a molecule is the chiral centre of that molecule. Chiral centre is a carbon atom of an organic compound that has four different substituents attached to it. Chiral compounds are compounds containing chiral carbon atoms. Chirality is actually the property of having chiral centres. The chiral centre is essentially sp3 hybridized because it has to bear four different groups of atoms, forming four single covalent bonds.

Chiral centres cause the optical isomerism of compounds. In other words, compounds having chiral centres do not superimpose with their mirror image. Therefore, compounds having the chiral centre and the molecule that resembles its mirror image are two different compounds. Together, these two molecules are known as enantiomers.

On the other hand, the term achiral means that there are no chiral centres present. Therefore, a chiral compound has no symmetry. However, it has a non-superimposable mirror image. Since there are no chiral centres in achiral compounds, an achiral compound has superimposable mirror images.

What is the Difference Between Anomeric Carbon and Chiral Carbon?

Anomeric compounds and chiral compounds are two different forms of organic compounds that have specific types of carbon atoms. The key difference between anomeric carbon and chiral carbon is that an anomeric carbon atom essentially contains a hydroxyl group that is either cis or trans to the exocyclic oxygen atom, whereas a chiral carbon atom essentially contains four different functional groups attached to it with single covalent bonds.

The below infographic presents the differences between anomeric carbon and chiral carbon in tabular form for side by side comparison.

Summary – Anomeric Carbon vs Chiral Carbon

Anomeric compounds and chiral compounds are two different forms of organic compounds that have specific types of carbon atoms. The key difference between anomeric carbon and chiral carbon is that an anomeric carbon atom essentially contains a hydroxyl group that is either cis or trans to the exocyclic oxygen atom, whereas a chiral carbon atom essentially contains four different functional groups attached to it with single covalent bonds.

Reference:

1. “Chiral Carbon & Chiral Drugs | Stereochemistry (Article).” Khan Academy.

Image Courtesy:

1. “Anomerism V.2” By Jü – Own work (CC0) via Commons Wikimedia
2. “Itraconazole chiral carbons” By Vaccinationist – Own work (CC BY-SA 4.0) via Commons Wikimedia