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Chapter 7: Problem 104

State whether the following statements are true or false? (i) Glucose is the only aldose that shows mutarotation. (ii) The smallest aldose to form a hemiacetal is a tetrose. (iii) a-D-glucose \(\rightleftharpoons\) aldehyde form \(\rightleftharpoons\) b-D- glucose. This conversion is known as mutarotation. (iv) The anomers of D-glucose have specific rotations of same magnititude but opposite sign. (v) Sucrose is a 1,4 '-glycoside. (vi) In alkaline medium, fructose is a reducing sugar. (vii) Cellobiose is a polysaccharide. (viii) Natural sugar has D-configuration.

Short Answer

Expert verified
A. Statement 1: Glucose is the only aldose that shows mutarotation B. Statement 4: The anomers of D-glucose have specific rotations of the same magnitude but opposite sign C. Statement 7: Cellobiose is a polysaccharide D. Statement 8: Natural sugar has D-configuration

Step by step solution

01

1. Glucose is the only aldose that shows mutarotation

False. Mutarotation is the change in the specific rotation of a compound as it interconverts between its alpha and beta anomers in an equilibrium. Several aldoses, including glucose, show mutarotation. Other aldoses such as galactose and mannose also exhibit mutarotation.
02

2. The smallest aldose to form a hemiacetal is a tetrose

True. Hemiacetals form when an aldehyde reacts with an alcohol. In the case of aldoses, this occurs when the carbonyl group reacts with the hydroxyl group on a different carbon. The smallest aldose to form a hemiacetal is a tetrose (four-carbon sugar) since it has at least two carbons apart to allow the formation of a hemiacetal ring structure.
03

3. a-D-glucose \(\rightleftharpoons\) aldehyde form \(\rightleftharpoons\) b-D-glucose. This conversion is known as mutarotation

True. Mutarotation is the interconversion between alpha and beta anomers of a compound. In this case, the statement correctly states that alpha-D-glucose can interconvert to its open-chain aldehyde form, which can then interconvert to its beta-D-glucose form.
04

4. The anomers of D-glucose have specific rotations of the same magnitude but opposite sign

True. Specific rotation is a measure of the optical rotation of a compound when polarized light is passed through it. For D-glucose anomers, the specific rotations are indeed of the same magnitude but opposite sign: +112.2° for alpha-D-glucose and -18.7° for beta-D-glucose.
05

5. Sucrose is a 1,4 '-glycoside

True. Sucrose is a disaccharide composed of glucose and fructose units linked by an alpha-1,2-glycosidic bond, also known as a 1,4 '-glycoside.
06

6. In alkaline medium, fructose is a reducing sugar

True. A reducing sugar is a sugar that can reduce other compounds and be oxidized itself. Fructose, an isomer of glucose, can act as a reducing sugar in an alkaline medium as it has an open chain aldehyde or ketone group that can be oxidized.
07

7. Cellobiose is a polysaccharide

False. Cellobiose is a disaccharide (two sugar units) consisting of two glucose molecules linked by a beta-1,4-glycosidic bond. A polysaccharide consists of many sugar units. Examples of polysaccharides include starch, cellulose, and glycogen.
08

8. Natural sugar has D-configuration

True. Most natural sugars exist in the D-configuration. This means that the hydroxyl group on the chiral carbon furthest from the carbonyl group is on the right side. Examples include D-glucose, D-galactose, and D-fructose.

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Most popular questions from this chapter

Write the steps involved in the conversion of D-glucose to D-fructose.

Polymers are classified in a number of ways. On the basis of structures, they are divided into three types: linear polymers, branched chain polymers and cross linked polymers. Depending upon the nature of the repeating structural unit, polymers are classified as homopolymers and copolymers. Based on the magnitude of the intermolecular forces, they are classified into four types namely elastomers, fibres, thermoplastics and thermosetting plastics. Polymers are again classified as addition polymers and condensation polymers depending on the mode of polymerization. The different linear chains of terylene molecules are held together by (a) van der Waals forces (b) covalent bonds (c) hydrogen bonds (d) dipole-dipole interaction

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Each question contains Statement- 1 and Statement-2 and has the following choices (a), (b), (c) and (d), out of which ONLY ONE is correct. (a) Statement- 1 is True, Statement- 2 is True; Statement- 2 is a correct explanation for Statement- 1 (b) Statement- 1 is True, Statement- 2 is True; Statement- 2 is NOT a correct explanation for Statement-1 (c) Statement- 1 is True, Statement- 2 is False (d) Statement- 1 is False, Statement- 2 is True Statement 1 Tollen's test can be used to distinguish between glucose and fructose. and Statement 2 Glucose is an aldose while fructose is a ketose.

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