Exam 4 Chem 115 – Carbohydrates, Lipids, Proteins, and Nucleic Acids Study Guide

Q6. Glucose can have the structure shown here. It can be classified as ________.

Background

Topic: Carbohydrate Structure and Stereochemistry

This question tests your ability to identify and classify the cyclic form of glucose based on its stereochemistry (alpha/beta, D/L forms).

Key Terms and Concepts:

• Haworth Projection: A common way to represent the cyclic structure of sugars.

• Alpha (α) vs. Beta (β): Refers to the orientation of the anomeric hydroxyl group (OH) relative to the CH2OH group.

• D- and L-: Refers to the configuration of the chiral carbon farthest from the carbonyl group (usually C-5 in hexoses).

Step-by-Step Guidance

1. Identify the anomeric carbon (the carbon attached to two oxygens in the ring; in glucose, this is C-1).

2. Determine if the OH group on the anomeric carbon is pointing down (α) or up (β) in the Haworth projection.

3. Locate the CH2OH group (carbon 6). If it is above the ring, the sugar is in the D-configuration; if below, it is L-configuration.

4. Combine your findings to classify the structure as α-D, β-D, α-L, or β-L glucose.

Try solving on your own before revealing the answer!

Final Answer: α-D-glucose

The OH on the anomeric carbon (C-1) is down, and the CH2OH group is up, indicating α-D-glucose.