Question

How will you confirm the presence of five –OH groups in a glucose molecule, which are attached to different carbon atoms?

Hint:

Glucose + Acetic anhydride → Glucose pentaacetate Confirms 5 –OH groups.

Answer 1

Step 1: Understanding the Structure of Glucose.
Glucose is a monosaccharide with the molecular formula \( C_6H_{12}O_6 \). It contains six carbon atoms, one of which is part of a carbonyl group (aldehyde), and the others are bonded to hydroxyl (-OH) groups.

Step 2: Identifying the Hydroxyl Groups.
To confirm the presence of five –OH groups in glucose, we need to look at the structure of glucose. The glucose molecule has five hydroxyl groups attached to different carbon atoms, and they can be confirmed by:
1. Structural Analysis: By drawing or reviewing the chemical structure of glucose (either in its open-chain or cyclic form), we can identify the positions of the hydroxyl groups. In the open-chain form, glucose has –OH groups at carbon atoms 2, 3, 4, and 6, with the fifth –OH attached at carbon 6 in the cyclic form.

Step 3: Chemical Tests for Hydroxyl Groups.
Chemical tests can also confirm the presence of hydroxyl groups in glucose:
1. Reaction with Sodium Metal: When glucose reacts with sodium metal, hydrogen gas is released due to the reaction with hydroxyl groups. This reaction confirms the presence of –OH groups in the molecule.
2. Using Phenolphthalein: When glucose is mixed with phenolphthalein and a base, the color change from colorless to pink can indicate the presence of hydroxyl groups, as the phenolphthalein interacts with the hydroxyl groups under basic conditions.

Conclusion.
The presence of five –OH groups in glucose can be confirmed both by structural analysis and chemical reactions like reacting with sodium or using phenolphthalein. These methods will highlight the interactions involving the hydroxyl groups.