One or more options correct
Select the correct statement(s) about carbohydrates and polymers.
- A. Sucrose shows mutarotation because it has a free hemiacetal group on its fructose unit.
- B. D-Glucose, D-mannose and D-fructose all give the same osazone with excess phenylhydrazine.
- C. Cellulose consists of -D-glucose units joined through glycosidic links.
- D. Natural rubber is a polymer of isoprene in which all the double bonds have trans configuration.
Show answer and solution
Answer: B
(A) In sucrose the anomeric carbons of glucose (C-1) and fructose (C-2) are joined to each other through the glycosidic oxygen, so neither unit has a free hemiacetal group; sucrose is non-reducing and does not show mutarotation; false. (B) Osazone formation with excess involves only C-1 and C-2. D-Glucose and D-mannose differ only at C-2, and D-fructose has the carbonyl at C-2; after conversion the C-1 and C-2 carbons become identical and groups, with C-3 to C-6 unchanged, so all three give the same osazone; true. (C) Cellulose has -D-glucose units linked -1,4; false. (D) Natural rubber is cis-1,4-polyisoprene (gutta-percha is the trans form); false.
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