Properties of Glucose MCQ - Practice Questions & Answers

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Chemical Properties of Glucose is considered one of the most asked concept.
27 Questions around this concept.

Concepts Covered - 4

Evidence for Open Chain Structure of Glucose

Glucose, on complete reduction with HI and red phosphorus, finally n-hexane. This indicates that it contains a straight chain of six carbon atoms.
It reacts with acetic anhydride and forms penta-acetate derivate. This shows the presence of five hydroxyl groups each linked to a separate carbon atom as the molecule is stable.
Glucose combines with one mole of HCN to form a cyanohydrin. These reactions indicate the presence of a carbonyl group, C=O, in the glucose molecule.
Mild oxidation of glucose with bromine water gives gluconic acid. Further, glucose also reduces Tollen's reagent and Fehling's solution. These reactions show the presence of an aldehyde group.

Evidence for Ring Structure of Glucose

Glucose does not react with sodium bisulphite. It confirms the absence of -CHP group.
Glucose does not give Schiff's test and DNP test. It confimrs the absence of -CHO group.
Glusoce pentaacetate does not react with hydroxylamine. It means absence of -CHO group.

Chemical Properties of Glucose

Glucoside formation
Glucose reacts with methanol in the presence of HCl and gives α and β glucoside. Glucoside formation is due to the reaction of alcohol with glucoside -OH group of glucose. β,D glucose forms β,D-methyl glucoside.
Reduction
Monosaccharides can be reduced by various reducing agents such as sodium-amalgam or by hydrogen under high pressure in the presence of catalysts.
Reaction with nitric acid
When glucose is oxidised with nitric acid, saccharic acid is formed. Saccharic acid is also known as glucaric acid.
Ester formation
They can form esters with carboxylic acids due to the presence of OH groups. For eg. glucose reacts with five molecules of acetic anhydride to form pentaacetate derivative. It indicates that the glucose contains five OH groups.

Diasaccharides and Polysaccharides

Disaccharides
The disaccharides consist of two molecules of monosaccharides. When hydrolysed with enzymes or dilute acids, they give two molecules of either same or varying monosaccharides. Some examples include,

$\mathrm{C_{12}H_{22}O_{11}\: \overset{H_{2}O}{\longrightarrow}\: C_{6}H_{12}O_{6}\: +\: C_{6}H_{12}O_{6}}$
Sucrose Glucose Fructose

$\mathrm{C_{12}H_{22}O_{11}\: \overset{H_{2}O}{\longrightarrow}\: C_{6}H_{12}O_{6}\: +\: C_{6}H_{12}O_{6}}$
Lactose Glucose Galactose

On the basis of the position of linkages between the two monosaccharide units, the disaccharides might be reducing or non-reducing in nature. The resultant disaccharide is non-reducing if the glycosidic linkage involves the carbonyl functions of both monosaccharide units. On the other hand, the resulting disaccharide is the reducing sugar, e.g., maltose and lactose, if one of the carbonyl functions in either of the monosaccharide units is free.

Polysaccharides
Polysaccharides are the carbohydrates having hundreds or even thousands of monosaccharide units joined together by glycosidic linkages, e.g., starch, cellulose, glycogen and dextrins. However, starch and cellulose are the most important polysaccharides.