Question

Which carbon atoms of glucose, numbered from 1 to 6 forms a hemiacetal structure between -CHO and -OH groups.?

• A. C-2
• B. C-3
• C. C-4
• D. C-5

Hint:

The aldehyde carbon C-1 reacts with the hydroxyl on C-5 to form the six-membered pyranose ring.

Answer 1

The Correct Option is D

Step 1: Count ring size.
A ring formed by C-1 and the oxygen on C-n has (n) carbons plus 1 oxygen, i.e. n + 1 atoms.

Step 2: Find the stable one.
For n = 5 the ring has 6 atoms, which is strain free. Smaller rings (n = 2, 3, 4) are unstable.

Final Answer:
Option (D). \[ \boxed{\text{C-5}} \]