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Monosaccharide Configurations quiz

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  • What are the two systems used to designate monosaccharide configurations?
    The Cahn-Ingold-Prelog system (R/S) and Fisher's convention (D/L) are used to designate monosaccharide configurations.
  • How are priorities assigned to groups attached to a chiral carbon in the Cahn-Ingold-Prelog system?
    Priorities are assigned based on the atomic numbers of the atoms directly attached to the chiral carbon; higher atomic numbers get higher priority.
  • What configuration is assigned if the sequence from priority 1 to 2 to 3 is clockwise?
    A clockwise sequence corresponds to the R configuration.
  • What configuration is assigned if the sequence from priority 1 to 2 to 3 is counterclockwise?
    A counterclockwise sequence corresponds to the S configuration.
  • In a Fischer projection, what does a horizontal bond represent?
    A horizontal bond in a Fischer projection represents a wedge, meaning it is popping out of the page.
  • What adjustment must be made if the lowest priority group is on a wedge in a Fischer projection?
    If the lowest priority group is on a wedge, you must assign the opposite configuration to what the sequence appears to be.
  • How does Fisher's convention assign D and L configurations to chiral carbons?
    D is assigned when the hydroxyl group is on the right, and L is assigned when the hydroxyl group is on the left in a standard Fischer projection.
  • What is the reference molecule for D and L configurations in carbohydrates?
    Glyceraldehyde is the reference molecule for D and L configurations in carbohydrates.
  • What must be true for Fisher's convention to work properly?
    Fisher's convention only works with standard Fischer projections, where the carbonyl group is at the top and the longest carbon chain is vertical.
  • How is the overall configuration of a monosaccharide determined when multiple chiral carbons are present?
    The overall configuration is determined by the chiral carbon furthest from the carbonyl group.
  • What is the usual correlation between D/L and R/S configurations in carbohydrates?
    Usually, D corresponds to R and L corresponds to S, but this is not always true and should be verified independently.
  • Which configuration is preferred for biological carbohydrates?
    Biological carbohydrates are usually found in the D configuration.
  • Which configuration is preferred for biological amino acids?
    Biological amino acids are usually found in the L configuration.
  • What is the significance of the carbonyl group’s position in a standard Fischer projection?
    The carbonyl group must be at the top for the projection to be considered standard, which is necessary for proper D/L assignment.
  • Why is it important to determine R/S and D/L configurations separately?
    Because the correlation between D/L and R/S is not always exact, determining them separately ensures accuracy.