Carbohydrates are optically active polyhydroxy aldehydes or ketones or molecules that provide such units on hydrolysis. They are broadly classified into three groups: monosaccharides, oligosaccharides and polysaccharides. Monosaccharide units are held together by glycosidic linkages to form disaccharides or polysaccharides. Starch and cellulose are polysaccharides. Starch is a polymer of $\alpha$-glucose and consists of two components: Amylose and Amylopectin. Amylose is water soluble, having 15--20% of starch, whereas Amylopectin is insoluble in water, having 80--85% starch. Chemically, amylose is a long unbranched chain of $\alpha$-glucose units held together by C$_1$--C$_4$ glycosidic linkage. Amylopectin is a branched chain of $\alpha$-glucose units held together by C$_1$--C$_4$ and C$_1$--C$_6$ glycosidic linkages.
Write two differences between Amylose and Amylopectin.
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Solution and Explanation
Structural components of starch.
Step 2: Analysis
Amylose is the water-soluble, unbranched component. Amylopectin is the water-insoluble, branched component.
Final Answer: 1. Amylose is water-soluble, whereas amylopectin is insoluble in water. 2. Amylose is a long unbranched chain held by C1-C4 glycosidic linkages, whereas amylopectin is a branched chain held by C1-C4 and C1-C6 glycosidic linkages.
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Write IUPAC names of the following compounds and classify them into primary, secondary and tertiary amines.
(i) (CH3 )2CHNH2 (ii) CH3 (CH2 )2NH2 (iii) CH3NHCH(CH3 )2
(iv) (CH3 )3CNH2 (v) C6H5NHCH3 (vi) (CH3CH2 )2NCH3 (vii) m–BrC6H4NH2
Give one chemical test to distinguish between the following pairs of compounds.
(i) Methylamine and dimethylamine
(ii) Secondary and tertiary amines
(iii) Ethylamine and aniline
(iv) Aniline and benzylamine
(v) Aniline and N-methylanilineAccount for the following:
(i) pKb of aniline is more than that of methylamine.
(ii) Ethylamine is soluble in water whereas aniline is not.
(iii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.
(iv) Although amino group is o– and p– directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline.
(v) Aniline does not undergo Friedel-Crafts reaction.
(vi) Diazonium salts of aromatic amines are more stable than those of aliphatic amines. (vii) Gabriel phthalimide synthesis is preferred for synthesising primary amines.
Top CBSE CLASS XII Carbohydrates Questions
Which one of the following is a disaccharide? \[ \text{Glucose, Lactose, Amylose, Fructose} \]
- In the Haworth structure of the following carbohydrate, various carbon atoms have been numbered. The anomeric carbon is numbered as:
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- On hydrolysis, which of the following carbohydrates gives only glucose ?
- Identify the polysaccharide among the following :
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