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

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Discussion Overview

The discussion revolves around the stereochemistry of D and L glucose, specifically addressing the relationship between the configuration of hydroxyl (OH) groups and chirality centers in these molecules. Participants explore the implications of enantiomerism and the conventions used in naming stereoisomers in biochemistry.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions the relationship between the last chirality center and the configuration of other hydroxyl groups in D and L glucose.
  • Another participant explains that D- and L-glucose are enantiomers, meaning their configurations are switched at all stereocenters.
  • A further reply acknowledges the previous explanation but seeks clarification on the significance of the last chiral carbon in the naming convention.
  • Another participant suggests that the choice of the last chiral carbon for nomenclature is somewhat arbitrary, noting that most naturally occurring aldohexoses share the same configuration at that position.
  • A light-hearted comment is made in response to the previous points, indicating a friendly tone in the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the significance of the last chiral carbon in the context of D and L nomenclature, indicating that the discussion remains unresolved regarding the importance of this aspect.

Contextual Notes

The discussion highlights the arbitrary nature of naming conventions in biochemistry and the potential for confusion regarding stereochemistry in glucose. There are unresolved assumptions about the implications of chirality and the choice of reference points in nomenclature.

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Because D- and L-glucose are enantiomers (i.e. mirror images), their configuration is switched at all stereocenters of the molecule.
 
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?
 
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.
 
You are too kind, sir.
 

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