JEE Main 2022 · 28 Jul · Shift 1 · Chemistry Q78

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ChemistrySingle correct+4 / -1Question 78 of 90

For the below given cyclic hemiacetal (X), the correct pyranose structure is :

Fischer projection of hemiacetal X: C1 (HO-C-H) bonded through the ring O to C5; C2 HO-C-H, C3 H-C-OH, C4 HO-C-H, C5 H-C, C6 CH2OH.

Pyranose (A)

Chair-like pyranose with CH2OH at C5; ring OH groups drawn up/down in pattern A (stereochemistry not encoded in the SMILES).

Pyranose (B)

Chair-like pyranose with CH2OH at C5; ring OH groups drawn up/down in pattern B (stereochemistry not encoded in the SMILES).

Pyranose (C)

Chair-like pyranose with CH2OH at C5; ring OH groups drawn up/down in pattern C (stereochemistry not encoded in the SMILES).

Pyranose (D)

Chair-like pyranose with CH2OH at C5 and an extra HO on C4 drawn up; ring OH groups in pattern D (stereochemistry not encoded in the SMILES).

Answer and worked solution

Official answer: D

X in the Fischer projection. OH on the right at C3; on the left at C1, C2 and C4; the ring oxygen on the right at C5. This is a D-hexopyranose (β-D-idopyranose).

Haworth rule. Right-hand groups go down and left-hand groups go up: OH up at C1, C2 and C4, down at C3, with $\mathrm{CH_2OH}$ up. Option (D) matches.

(D)

Topics:Carbohydrates

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JEE Main 2022 · 28 Jul · Shift 1, Chemistry question 78