Question: In the Haworth structure of the following carbohydrate, various carbon atoms have been numbered. The anomeric carbon is numbered as :
Step 1 (Definition & Governing Principle): [0.5 Mark]
The anomeric carbon is defined as the carbon atom derived from the carbonyl carbon (the functional group carbon) of the open-chain form of a sugar. In the cyclic Haworth projection of an aldose (like glucose), this carbon is the one bonded to both the ring oxygen and a hydroxyl group ($-OH$). By IUPAC convention for cyclic sugars, this carbon is assigned the lowest possible number, which is 1.
Step 2 (Step-by-Step Identification): [0.25 Mark]
- In the open-chain structure of D-glucose, the aldehyde group is at $C_1$.
- Upon cyclization to form a pyranose ring, the $C_1$ aldehyde carbon reacts with the $C_5$ hydroxyl group.
- In the resulting Haworth structure, the carbon adjacent to the ring oxygen atom (on the right side in standard orientation) is identified as $C_1$.
- Since $C_1$ is the chiral center formed at the carbonyl position, it is designated as the anomeric carbon.
Step 3 (Final Concluded Answer): [0.25 Mark]
Based on the standard numbering convention for monosaccharides in Haworth projections, the anomeric carbon is numbered as 1.
Correct Option: (A) 1
💡 EL10 Concept Insight: Think of the anomeric carbon as the "original boss" of the sugar molecule—it’s the carbon that used to be the reactive aldehyde or ketone before the sugar folded into a ring. Because it’s the most important part of the ring, we always give it the number 1 to start our counting!