The correct structure of D(+) Glucose is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Fischer projection with –OH right, left, right, right (C2 to C5)
In a Fischer projection of an aldohexose, the –CHO group (C1) is written at the top and –\( \ce{CH2OH} \) (C6) at the bottom; the four carbons C2–C5 in between are stereocentres. The letter D means that the –OH on the lowest stereocentre (C5) is on the right, as in D-glyceraldehyde. The sign (+) is the observed rotation (dextrorotatory) and is not read from the drawing.
D-(+)-Glucose has the –OH groups at C2, C3, C4 and C5 on the right, left, right, right:
\( \displaystyle \text{C2: OH right,}\quad \text{C3: OH left,}\quad \text{C4: OH right,}\quad \text{C5: OH right} \)
Only the structure in Option (1) has this pattern, so it is D-(+)-glucose.
Why the other options are incorrect
Option (2) –OH right, left, right, left — Incorrect. The –OH at C5 is on the left, so this is an L-sugar, not a D-sugar.
Option (3) –OH left, left, right, right — Incorrect. It differs from glucose only at C2; this is D-mannose, the C2 epimer of glucose.
Option (4) –OH left, right, left, right — Incorrect. It is a D-sugar, but C2, C3 and C4 are all reversed compared with glucose (it is D-idose).