Glucose - Open Chain and Cyclic Structure - UNSOLVED PRACTICE SET
Chapter: Biomolecules | Topic: Glucose Open Chain and Cyclic Structure
GLUCOSE - OPEN CHAIN AND CYCLIC STRUCTURE - UNSOLVED PRACTICE SET
Topic: Glucose Open Chain and Cyclic Structure
Multiple Choice Questions
Q1. The open-chain structure of glucose contains:
- One aldehyde group and four hydroxyl groups
- One aldehyde group and five hydroxyl groups
- One ketone group and five hydroxyl groups
- Two aldehyde groups and four hydroxyl groups
Q2. The cyclic structure of glucose is formed by the reaction of:
- C-1 aldehyde group with C-5 hydroxyl group
- C-1 aldehyde group with C-4 hydroxyl group
- C-2 hydroxyl group with C-5 hydroxyl group
- C-1 aldehyde group with C-6 hydroxyl group
Q3. The two cyclic forms of glucose, α-D-glucose and β-D-glucose, differ in the configuration at:
- C-1
- C-2
- C-3
- C-4
Q4. The phenomenon of mutarotation in glucose is due to:
- Conversion of D-glucose to L-glucose
- Interconversion between α and β forms through the open-chain form
- Hydrolysis of glucose
- Oxidation of glucose
Q5. The pyranose ring in glucose contains:
- Four carbon atoms and one oxygen atom
- Five carbon atoms and one oxygen atom
- Six atoms in total (5C + 1O)
- Five atoms in total (4C + 1O)
Q6. In the Haworth projection of β-D-glucose, the -OH group at C-1 is:
- Below the plane of the ring
- Above the plane of the ring
- In the plane of the ring
- Absent
Short Answer Questions
Q7. Draw the Fischer projection of D-glucose. Label the aldehyde group and the chiral centres.
Q8. Explain why glucose does not give a positive Schiff's test and sodium bisulphite addition test, despite having an aldehyde group.
Q9. What is mutarotation? Explain the process with reference to glucose.
Q10. Distinguish between α-D-glucose and β-D-glucose. Why are they called anomers?
Q11. The specific rotation of α-D-glucose is +112° and that of β-D-glucose is +19°. When either pure form is dissolved in water, the rotation gradually changes to +52.5°. Explain this observation.
Q12. Draw the Haworth projection of α-D-glucopyranose. Label the anomeric carbon and the glycosidic -OH group.
Long Answer Questions
Q13. (a) Draw the open-chain (Fischer projection) structure of D-glucose.
(b) Explain how the cyclic hemiacetal structure of glucose is formed from the open-chain form.
(c) Draw the Haworth projection of both α-D-glucopyranose and β-D-glucopyranose.
(d) Explain why glucose exists predominantly in the cyclic form in aqueous solution.
Q14. (a) What are anomers? How do α-D-glucose and β-D-glucose differ structurally?
(b) Explain the phenomenon of mutarotation with a suitable diagram showing the interconversion.
(c) The equilibrium mixture of glucose in solution contains approximately 36% α-form, 64% β-form, and only 0.02% open-chain form. Explain why the open-chain form is present in such a small amount.
Q15. (a) Describe the evidence that supports the cyclic structure of glucose. (Mention at least three points.)
(b) Glucose forms a cyanohydrin with HCN and reduces Tollens' reagent, yet it does not form an oxime immediately with hydroxylamine and does not give a positive Schiff's test. How do these observations support the cyclic structure of glucose?
Numerical / Application-Based Problems
Q16. The molecular mass of glucose is 180 g/mol.
(a) When glucose is treated with acetic anhydride, it forms a pentaacetate. What does this tell you about the number of -OH groups in glucose?
(b) Calculate the theoretical yield of glucose pentaacetate if 9.0 g of glucose is completely acetylated. (Molecular mass of pentaacetate = 390 g/mol)
(c) Glucose reacts with one mole of CH₃OH in the presence of dry HCl to form methyl glucoside. Explain why only one -OH group reacts and identify which -OH group is involved.
(d) If 3.6 g of glucose is converted to methyl glucoside, calculate the mass of product formed. (Molecular mass of methyl glucoside = 194 g/mol)
Q17. A student prepares a solution of pure α-D-glucose in water and measures its specific rotation at different time intervals:
| Time (min) | Specific Rotation (°) |
|---|---|
| 0 | +112 |
| 5 | +95 |
| 10 | +75 |
| 20 | +58 |
| 30 | +53 |
| 60 | +52.5 |
(a) Explain the change in specific rotation with time.
(b) What is the final specific rotation called? What is its significance?
(c) Calculate the percentage of α-form and β-form present at equilibrium, given that [α]α = +112° and [α]β = +19°.
(d) Why does the rotation not change after 60 minutes?
(e) If the student had started with pure β-D-glucose instead, sketch how the specific rotation would change with time.
Q18. In a school chemistry lab, students are studying the structure of glucose using various chemical tests.
(a) When glucose is treated with bromine water, what product is formed? What does this test confirm about the functional group in the open-chain form?
(b) When glucose is treated with nitric acid, a dicarboxylic acid (saccharic acid) is formed. What does this tell you about the terminal groups of glucose?
(c) Glucose does not react with NaHSO₃. How does this observation support the cyclic structure?
(d) The student adds glucose to Fehling's solution and heats it. A red precipitate forms. Write the reaction involved and explain what functional group is being tested.
(e) Based on all these tests, draw conclusions about the structure of glucose (both open-chain and cyclic aspects).