JEE Advanced · 2016 · 22 May 2016 · Paper 2 · Biomolecules

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For 'invert sugar', the correct statement(s) is(are)
(Given: specific rotations of (+)-sucrose, (+)-maltose, L-(-)-glucose and L-(+)-fructose in aqueous solution are

+ 6 6^{\circ}, + 14 0^{\circ}, - 5 2^{\circ}

and

+ 9 2^{\circ}

, respectively)

(A)'invert sugar' is prepared by acid catalyzed hydrolysis of maltose
(B)'invert sugar' is an equimolar mixture of D-(+)-glucose and D-(-)-fructose✓ Correct
(C)specific rotation of 'invert sugar' is -20°✓ Correct
(D)on reaction with $Br_{2}$ water, 'invert sugar' forms saccharic acid as one of the products

Answer: (B), (C)

Solution

Invert sugar is formed by acid-catalyzed hydrolysis of sucrose (not maltose):

C_{12} H_{22} O_{11} + H_{2} O H^{+} D - (+) -glucose + D - (-) -fructose

. It is an equimolar mixture. The specific rotation is the average:

\frac{+ 5 2 ^{\circ} + ( - 9 2 ^{\circ} )}{2} = - 2 0^{\circ}

. The name 'invert' comes from the inversion of optical rotation sign. Glucose reacts with

Br_{2}

water to form gluconic acid, not saccharic acid.

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JEE Advanced · 2016 · 22 May 2016 · Paper 2 · Biomolecules

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