Question

Represent α-D-(+)-glucopyranose and β-D-(+)-glucopyranose by Haworth structure.

Hint:

Draw the flat pyranose hexagon with ring O at top-right; the anomers differ only at C1 – OH down for α, OH up for β.

Answer 1

Step 1: The pyranose ring. Glucose exists as a six-membered ring (one ring oxygen + five carbons), called a pyranose. In the Haworth projection the ring is drawn as a flat hexagon lying almost perpendicular to the paper, with the ring oxygen at the upper right and C1 (the anomeric carbon) at the far right.
Step 2: Fixed groups (same in both forms). Number the ring carbons clockwise C1 to C5. For D-glucose:
• C2 –OH points down.
• C3 –OH points up.
• C4 –OH points down.
• C5 carries the –CH₂OH group pointing up (this defines the D-configuration).
Step 3: Difference at C1 (the anomeric carbon). The two forms (anomers) differ only in the direction of the –OH on C1:
• In α-D-(+)-glucopyranose, the C1 –OH points downwards (trans to the CH₂OH, i.e. on the opposite side).
• In β-D-(+)-glucopyranose, the C1 –OH points upwards (cis to the CH₂OH, i.e. on the same side).
Step 4: Summary of the Haworth structures.
α-D-glucopyranose: ring with O at top-right; C1–OH down, C2–OH down, C3–OH up, C4–OH down, C5–CH₂OH up, H atoms on the opposite side of each OH. \[ \boxed{\alpha\text{-form}: \text{C1--OH is down}} \]
β-D-glucopyranose: identical to the above except the C1–OH is up. \[ \boxed{\beta\text{-form}: \text{C1--OH is up}} \]