JEE Advanced 2026 — Paper 2 — CHEM-I solution

JEE Advanced2026Paper 2CHEM-I

A known artificial sweetener $X$ is composed of 4-chloro-4-deoxy- $α$ -D-galactose and 1,6-dichloro-1,6-dideoxy- $β$ -D-fructose joined by a glycosidic linkage. Structure of D-galactose is given below:

The correct structure of $X$ is:

A
(A)
B
(B)
C
(C)
D
(D)

Solution

Build the galactose half. Convert the Fischer projection of D-galactose to its pyranose (Haworth/chair) form. In $α$ -D-galactopyranose, the C1 anomeric OH is axial. To make 4-chloro-4-deoxy- $α$ -D-galactose, replace the C4 OH with Cl while keeping the C4 configuration. The chair therefore has Cl at C4, OH at C2 and C3, and CH $_{2}$ OH at C5.

Build the fructose half. Take $β$ -D-fructofuranose. Replace the OH at C1 with Cl and at C6 with Cl, giving 1,6-dichloro-1,6-dideoxy- $β$ -D-fructofuranose. Both CH $_{2}$ Cl groups sit on the C1 and C6 carbons that hang outside the five-membered ring.

Form the glycosidic bond. Combine the C1 of the galactose ( $α$ ) with the C2 of the fructose ( $β$ ) through an O bridge with loss of H $_{2}$ O. This $α, β$ -1,2 glycosidic linkage matches the connectivity in sucralose.

Match. Only option (A) shows the galactopyranose with Cl at C4 (axial), correct $α$ -C1 linkage to a fructofuranose bearing CH $_{2}$ Cl groups at the C1 and C6 positions in the right stereochemistry.

$∴$ The answer is (A).

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