See image — Practical Organic Chemistry and Purification Chemistry Question

💡 Solution & Explanation

Step 1 – Define key stereochemical terms. • Anomers: stereoisomers that differ ONLY at the anomeric carbon (C1 in aldopyranoses). They are interconverted by mutarotation and are designated α and β. • Epimers: diastereomers that differ at exactly ONE non-anomeric stereocenter. Step 2 – Analyze structures I and III. Both structures I and III are methyl pyranosides with OMe at C1 (the anomeric carbon). Comparing the two chair drawings: in structure I the OMe is in the equatorial position (β-anomer), while in structure III the OMe is in the axial position (α-anomer). All other stereocenters (C2, C3, C4) bear the same spatial arrangement of OH groups in both I and III. Because the two structures differ only at the anomeric carbon C1, I and III are anomers (specifically α/β anomers of the same methyl glucopyranoside). Step 3 – Analyze structures I and II. Comparing I and II: the anomeric OMe position is the same (both equatorial/β). However, one of the ring OH groups (at a non-anomeric carbon, specifically C4 based on the HO orientation in the Haworth/chair drawings) is inverted between I and II — in I the HO is on one face, in II it is on the opposite face. All other stereocenters remain the same. Because they differ at exactly one non-anomeric carbon, I and II are epimers. Step 4 – Confirm option (c). Option (c) states: "I and III are anomers; I and II are epimers." This matches the analysis in Steps 2 and 3 exactly. Step 5 – Eliminate other options. (a) Claims I and II are anomers — incorrect; they differ at a non-anomeric center. (b) Claims III and IV are anomers — this may also be true, but the first part (I and II are epimers) combined with the second part is less precisely stated, and option (b) omits the I–III anomer relationship. (d) Claims I and III are epimers — incorrect; they differ at the anomeric carbon, making them anomers not epimers. Therefore, the correct answer is C.