Question

(a) What is meant by invert sugar ?

(b) What happens when glucose reacts with nitric acid ? Write the reaction involved.

(c) Name the disease caused by the deficiency of Vitamin \( \mathrm{B_1} \).

Hint:

Invert sugar is the laevorotatory glucose plus fructose mixture from sucrose hydrolysis. Nitric acid oxidises glucose to saccharic acid. Lack of vitamin B1 causes beriberi.

Answer 1

Step 1: Understanding the Question:
Three one-mark parts are asked from Biomolecules: a definition about sucrose hydrolysis, an oxidation reaction of glucose, and a vitamin deficiency disease.

Step 2: Part (a) - Invert sugar:
Sucrose is dextrorotatory, with a specific rotation of \( +66.5^\circ \).
On hydrolysis with dilute acid or the enzyme invertase, it gives an equimolar mixture of D-(+)-glucose and D-(-)-fructose.
\[ \mathrm{C_{12}H_{22}O_{11} + H_2O \xrightarrow{H^+} C_6H_{12}O_6\ (glucose) + C_6H_{12}O_6\ (fructose)} \]
Glucose rotates the plane of light by \( +52.5^\circ \) and fructose by \( -92.4^\circ \). The mixture therefore turns laevorotatory (net about \( -20^\circ \)).
Because the sign of rotation is inverted from + to -, this mixture is called invert sugar.

Step 3: Part (b) - Glucose with nitric acid:
Nitric acid is a strong oxidising agent. It oxidises both the aldehyde group and the terminal primary alcohol group of glucose.
So glucose is oxidised to saccharic acid (glucaric acid), a dicarboxylic acid with six carbon atoms.
\[ \mathrm{CHO(CHOH)_4CH_2OH \xrightarrow{HNO_3} HOOC(CHOH)_4COOH} \]

Step 4: Part (c) - Vitamin B1 deficiency:
Vitamin \( \mathrm{B_1} \) is thiamine. Its lack causes the disease beriberi, with loss of appetite, weak muscles and nerve damage.

Final Answer:
(a) Invert sugar is the equimolar mixture of D-glucose and D-fructose from hydrolysis of sucrose. (b) Glucose is oxidised to saccharic acid, \( \mathrm{HOOC(CHOH)_4COOH} \). (c) Beriberi.