Question

In the ring structure of fructose, the anomeric carbon is :

• A. C2
• B. C3
• C. C4
• D. C1

Hint:

For aldoses like glucose, the anomeric carbon is C1. For ketoses like fructose, the anomeric carbon is C2.

Answer 1

The Correct Option is A

Step 1: Define anomeric carbon.
The anomeric carbon is the new chiral centre created during cyclisation of a monosaccharide. It corresponds to the carbon that bore the carbonyl group (aldehyde in aldoses, ketone in ketoses) in the open-chain form.
Step 2: Classify fructose.
Fructose is a ketohexose. In its open-chain linear form, the carbonyl group is a ketone at carbon 2 (C2), following IUPAC numbering where the terminal $-CH_2OH$ closer to the carbonyl is C1.
Step 3: Identify the ring-closure reaction.
To form the five-membered furanose ring, the $-OH$ group on C5 attacks the C2 carbonyl carbon in an intramolecular nucleophilic addition, producing a hemiketal at C2.
Step 4: Identify the anomeric carbon.
The hemiketal carbon created at C2 is the new stereogenic centre; it is the anomeric carbon of fructose in its cyclic (furanose) form.
\[ \boxed{\text{C2}} \]