Lecture on Absolute Configuration of D-Glucopyranose

Introduction

• Focus on determining the absolute configuration of the new stereogenic carbon (carbon number one) formed in alpha and beta anomers of D-glucopyranose.
• Analyze both straight chain and ring forms of D-glucose.

Understanding D-Glucose

• D-Glucose Characteristics:
  • Six carbons, with the stereogenic carbons at positions 2, 3, 4, and 5.
  • D designation: Hydroxy group points to the right.
  • L designation: Hydroxy group points to the left.
• Non-stereogenic Carbons:
  • Carbon 1 and Carbon 6 are not stereogenic in the straight chain form.

Formation of Anomers

• Intramolecular Nucleophilic Reaction:
  • Hydroxide acts as a nucleophile.
  • Attack from the bottom forms beta-D-glucopyranose.
  • Attack from the top forms alpha-D-glucopyranose.
• New Stereogenic Carbon (Carbon 1):
  • In the ring form, carbon number one becomes stereogenic, increasing the number of stereogenic carbons to five.

Configuration of Stereogenic Carbon

• Priority Rules:
  • Rank groups from least to greatest priority.
  • H atom (least priority), Oxygen (highest priority).
• Beta Anomer:
  • Priority: 1 (oxygen), 2 (carbon), 3, 4 (hydrogen).
  • Configuration Process:
    • Orient so that the least priority group is pointing into the board.
    • Determine the configuration direction (1 to 3 pattern).
    • Beta D-glucopyranose Configuration: R (clockwise).
• Alpha Anomer:
  • Configuration is opposite that of beta.
  • Alpha D-glucopyranose Configuration: S (counterclockwise).

Conclusion

• Beta anomer of D-glucopyranose has an R configuration on the first stereogenic carbon.
• Alpha anomer has an S configuration on the first stereogenic carbon.
• Understanding of configurations is crucial in stereochemistry and molecular interactions.