JEE Main · 2023 · 25 Jan 2023 · Shift 1 · Biomolecules

Glucose closes to a six-membered pyranose ring and fructose to a five-membered furanose ring, while within each pair the anomers differ only in the orientation of the hydroxyl at the anomeric carbon, pointing down in the $\alpha$ form and up in the $\beta$ form. The two six-membered rings are therefore the glucopyranoses and the two five-membered rings the fructofuranoses. Reading the anomeric hydroxyl in each, the structures correspond to P being $\alpha$-D-glucopyranose, Q being $\beta$-D-glucopyranose, R being $\alpha$-D-fructofuranose and S being $\beta$-D-fructofuranose.