Question

Two forms of D-glucopyranose, are called

• A. enantiomers
• B. anomers
• C. epimers
• D. diastereomers
• E. tautomers

Hint:

Chemistry Tip: In sugars, $\alpha$ and $\beta$ forms that differ only at C-1 (anomeric carbon) are called anomers.

Answer 1

The Correct Option is B

Concept:
D-glucose exists in cyclic hemiacetal forms. When glucose cyclises, it commonly forms a six-membered ring called D-glucopyranose. During ring formation, the carbonyl carbon of open-chain glucose becomes a new chiral center called the anomeric carbon (C-1). Because of this new stereocenter, two different cyclic forms are possible.
Step 1: Formation of cyclic glucose.
Open-chain D-glucose contains an aldehyde group at C-1. Intramolecular reaction between:

• aldehyde group at C-1
• hydroxyl group at C-5

forms a cyclic hemiacetal ring: $$\text{D-glucose} \rightarrow \text{D-glucopyranose}$$
Step 2: Two possible orientations at C-1.
At the newly formed anomeric carbon (C-1), the OH group can be arranged in two ways:

• \(\alpha\)-D-glucopyranose
• \(\beta\)-D-glucopyranose

These two forms differ only in configuration at the anomeric carbon.
Step 3: Definition of anomers.
Stereoisomers that differ only at the anomeric carbon atom are called: $$\boxed{\text{Anomers}}$$ Thus the two forms of D-glucopyranose are $\alpha$ and $\beta$ anomers.
Step 4: Why other options are wrong?}}

• Enantiomers: non-superimposable mirror images.
• Epimers: differ at one chiral carbon other than anomeric carbon (general term).
• Diastereomers: stereoisomers not mirror images.
• Tautomers: interconvert by proton shift and bond migration.

The most specific correct term here is anomers.
Step 5: Final answer.
Hence, two forms of D-glucopyranose are called: $$\boxed{\text{Anomers}}$$ Therefore correct option is: $$\boxed{\text{(B)}}$$