Question

α-D-(+) Glucose and β-D-(+) Glucose are:

• A. Enantiomers
• B. Epimers
• C. Conformational isomers
• D. Anomers

Hint:

To remember which is which in Haworth projections: - α: The hydroxyl group is "Fish" (Down/Alpha). - β: The hydroxyl group is "Bird" (Up/Beta).

Answer 1

The Correct Option is D

Concept: Glucose exists in a cyclic hemiacetal form produced by the reaction between the -OH group at C-5 and the -CHO group at C-1. This cyclization creates a new chiral center at the C-1 carbon, which is known as the anomeric carbon.
Anomers are a specific type of diastereomers that differ in configuration only at the hemiacetal or acetal carbon (the anomeric carbon). In the case of D-glucose: • α-D-Glucose: The -OH group at C-1 is on the opposite side of the CH₂OH group (axial in the chair conformation). • β-D-Glucose: The -OH group at C-1 is on the same side as the CH₂OH group (equatorial in the chair conformation).
• Enantiomers: These are non-superimposable mirror images. α and β glucose are not mirror images of each other. • Epimers: While anomers are a subset of epimers (diastereomers differing at one center), the term "Anomer" is the most specific and accurate description for sugars differing at the C-1 position. • Conformational isomers: These differ by rotation around single bonds (like chair and boat forms), whereas α and β forms require breaking and reforming bonds to interconvert.