Question

Which of the following represents the correct pyranose structure of \(\beta\)-D-(+) glucose?

• A. Structure 1
• B. Structure 2
• C. Structure 3
• D. Structure 4 \bigskip

Hint:

For D-sugars: \[ CH_2OH \text{ is always above the ring.} \] For \(\beta\)-anomers: \[ \text{Anomeric OH and } CH_2OH \] are on the same side of the ring. For \(\alpha\)-anomers: \[ \text{Anomeric OH and } CH_2OH \] are on opposite sides.

Answer 1

The Correct Option is C

Concept:

The cyclic six-membered ring form of glucose is known as glucopyranose. To identify the correct Haworth projection of \(\beta\)-D-(+) glucose, the following rules are used: 

• In D-glucose, the \(\mathrm{CH_2OH}\) group at C-5 lies above the plane of the ring.
• For D-sugars, groups present on the right side in the Fischer projection appear below the ring in Haworth form.
• Groups present on the left side in the Fischer projection appear above the ring.
• In the \(\beta\)-anomer, the anomeric \(-OH\) group and the \(\mathrm{CH_2OH}\) group are on the same side of the ring. 

Step 1: Write the Fischer projection configuration of D-glucose.

The arrangement of groups in D-glucose is: \[ \begin{array}{c|c} \text{Carbon} & \text{Position of OH} \\ \hline C_2 & \text{Right} \\ C_3 & \text{Left} \\ C_4 & \text{Right} \\ C_5 & \text{Right} \end{array} \] Using the Fischer-to-Haworth conversion rule: \[ \text{Right} \rightarrow \text{Down} \] \[ \text{Left} \rightarrow \text{Up} \] Therefore: \[ C_2: \ OH \downarrow \] \[ C_3: \ OH \uparrow \] \[ C_4: \ OH \downarrow \] \[ CH_2OH \uparrow \] 
Step 2: Apply the condition for the \(\beta\)-anomer.

For \(\beta\)-D-glucose, the anomeric OH at \(C_1\) must be on the same side as \(CH_2OH\). Since \(CH_2OH\) is above the ring, the anomeric OH must also be above the ring: \[ C_1: \ OH \uparrow \] 
Step 3: Compare all four structures.

• Structure 1 does not satisfy the required orientation of substituents.
• Structure 2 corresponds to a different anomeric arrangement.
• Structure 3 has: \[ CH_2OH \uparrow,\quad C_1OH \uparrow,\quad C_2OH \downarrow,\quad C_3OH \uparrow,\quad C_4OH \downarrow \] which exactly matches \(\beta\)-D-glucopyranose.
• Structure 4 has incorrect stereochemistry. 

Step 4: Select the correct structure.

Hence, the correct pyranose structure of \(\beta\)-D-(+) glucose is: \[ \boxed{\text{Structure 3}} \] Therefore, \[ \boxed{\text{Answer = (C)}} \]