See image — Biomolecules Chemistry Question

💡 Solution & Explanation

Step 1 - Concept: Anomers are a specific type of epimer that differ in configuration only at the anomeric carbon (C1 for aldoses, C2 for ketoses) of a cyclic sugar. They arise from the ring-closure (hemiacetal/hemiketal formation) and differ only in the orientation (α vs β) of the OH group at the anomeric carbon. Step 2 - Identify the given compound: The given structure is a five-membered furanose ring. The anomeric carbon (C1) has H pointing upward (toward the viewer on the top of the ring) and OH pointing downward. The other substituents (HO at C2, OH at C3, HOCH2 at C4) are all on the same face (below the ring plane), consistent with a specific furanose configuration (e.g., beta-D-ribofuranose or alpha, depending on convention). The key feature is the anomeric OH is DOWN (below the ring). Step 3 - What is needed: The anomer has the same ring size, same sugar identity, same configuration at all other stereocenters, but the OPPOSITE configuration at C1 (anomeric carbon). So we need the same furanose ring with all other OH groups in the same positions, but the anomeric OH now pointing UP. Step 4 - Evaluate options: - Option (a): Same furanose ring but C2 now has OH pointing UP — this changes configuration at C2, not only at C1. This is a different epimer, not simply the anomer. Incorrect. - Option (b): Same furanose ring (HOCH2 at C5, same ring size), same substituents at C2 (H bold/down), C3 (H and OH), but the anomeric position now shows OH pointing UP (top-right). This is exactly the opposite configuration at C1 only, with all other stereocenters unchanged — this is the anomer. Correct. - Option (c): This is a six-membered pyranose ring — different ring size entirely, so it cannot be the anomer of a furanose. Incorrect. - Option (d): Eliminated since option (b) is valid. Step 5 - Conclusion: Option (b) represents the same furanose sugar with all stereocenters identical except for C1 (anomeric carbon), where OH has flipped from down (alpha) to up (beta) or vice versa, making it the anomer. Therefore, the correct answer is B.