Question

The number of –OH groups in open chain and ring structures of D-glucose are respectively

• A. 4, 5
• B. 5, 4
• C. 5, 5
• D. 6, 5

Hint:

D-glucose exists in equilibrium between its open-chain and cyclic forms. The number of hydroxyl (-OH) groups remains the same in both forms except that the aldehyde group in the open-chain form converts into a hydroxyl group in the cyclic form.

Answer 1

The Correct Option is B

D-Glucose Functional Group Analysis

Step 1: Understanding the structure of D-glucose

D-glucose exists in two structural forms:

1. Open-chain form: The open-chain structure of D-glucose contains one aldehyde (-CHO) functional group and five hydroxyl (-OH) groups attached to the carbon atoms.
2. Cyclic (ring) form: When D-glucose undergoes cyclization to form a pyranose ring (as in the Haworth projection), the aldehyde group reacts with one of the hydroxyl groups to form a hemiacetal, resulting in the formation of a six-membered ring. In this form, the number of hydroxyl groups remains five.

Step 2: Identifying the correct answer

• In the open-chain form, there are five hydroxyl (-OH) groups.
• In the ring form, there are still five hydroxyl (-OH) groups (since the aldehyde group forms a hemiacetal but does not contribute an additional hydroxyl group).

Conclusion:

Thus, the correct answer is: (B) 5, 5