Why are all the OH opposite to each other in D and L glucose?

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In summary, the D and L in D- and L-glucose refer to the direction of the OH group on the last chirality center. However, because D- and L-glucose are enantiomers, their configuration is switched at all stereocenters of the molecule. While the naming convention for D- and L-glucose may seem arbitrary, it is based on the fact that most naturally occurring aldohexoses have the same configuration at the fifth carbon, leading to its use as the basis for the D/L system.
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  • #2
Because D- and L-glucose are enantiomers (i.e. mirror images), their configuration is switched at all stereocenters of the molecule.
 
  • #3
Ygggdrasil said:
Because D- and L-glucose are enantiomers (i.e. mirror images), their configuration is switched at all stereocenters of the molecule.

This makes sense. But then why do we care about the last chiral carbon?
 
  • #4
We don't. Like many thing in biology, the choice on how to name the different stereoisomers of glucose is somewhat arbitrary. It just turns out that, if you draw all of the naturally occurring aldohexoses in a Fisher projection, almost all of them have the same configuration about C5, so biochemists chose that position to use as the basis for the D/L nomenclature system.
 
  • #5
You are too kind, sir.
 

FAQ: Why are all the OH opposite to each other in D and L glucose?

1. Why are the OH groups in D and L glucose arranged in opposite positions?

The arrangement of OH groups in D and L glucose is a result of the chiral nature of these molecules. D and L glucose are enantiomers, meaning they have the same chemical formula and structure but are mirror images of each other. Therefore, the OH groups are arranged in opposite positions to maintain this mirror image relationship.

2. What is the significance of the OH group arrangement in D and L glucose?

The arrangement of OH groups in D and L glucose is important for their biological function. The different orientations of the OH groups affect how these molecules interact with enzymes and other biomolecules, ultimately influencing their ability to participate in biochemical reactions.

3. Is the OH group arrangement in D and L glucose related to their optical activity?

Yes, the OH group arrangement in D and L glucose is directly related to their optical activity. D and L glucose have different optical rotations because of their opposite OH group arrangements, with D glucose having a positive rotation and L glucose having a negative rotation.

4. Can the OH group arrangement in D and L glucose change?

No, the OH group arrangement in D and L glucose cannot change without altering the entire structure of the molecule. The arrangement of OH groups is a fundamental characteristic of these molecules and is determined by the positions of the carbon atoms in the molecule.

5. How does the OH group arrangement in D and L glucose affect their physical properties?

The OH group arrangement in D and L glucose plays a significant role in their physical properties, such as solubility, melting point, and boiling point. This is because the orientation of the OH groups influences the overall shape and structure of the molecule, which in turn affects its interactions with other molecules and substances.

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