Carbohydrates: Glucose and Fructose

Glucose (C₆H₁₂O₆)

1. Reaction with Cu(OH)₂:

• 2C₆H₁₂O₆ + Cu(OH)₂ → (C₆H₁₂O₆)₂Cu + 2H₂O

• Observation: The blue Cu(OH)₂ precipitate dissolves, forming a blue solution.

• Note: This reaction is characteristic of polyfunctional compounds with multiple adjacent -OH groups. Glucose exhibits this reaction due to its multiple hydroxyl groups.

2. Alcoholic Fermentation:

• C₆H₁₂O₆ —-enzyme, 25-35 degrees Celsius —> C₂H₅OH + CO₂

• Reaction Name: Alcoholic fermentation.

• Note: This reaction occurs under the influence of enzymes and at a suitable temperature. Yeast is a common source of the necessary enzymes for this process.

3. Silver Mirror Test:

• C₆H₁₂O₆ + 2[Ag(NH₃)₂]OH —-> C₅H₁₁O₅COONH₄ + 2Ag + 3NH₃ + H₂O

• Note: This reaction demonstrates the presence of an aldehyde (-CHO) group in glucose.

4. Reaction with Bromine:

• C₆H₁₂O₆ + Br₂ + H₂O —> C₆H₁₂O₇ + 2HBr

• Note: Glucose is oxidized by bromine water to form gluconic acid, further confirming the presence of an aldehyde group.

5. Hydrogenation Reaction:

• C₆H₁₂O₆ + H₂ —-Ni, t degree—-> C₆H₁₄O₆ (sorbitol / glucitol)

• Note: This is a hydrogenation reaction, resulting in the formation of a polyol (sugar alcohol). Sorbitol is a commonly used sugar substitute.

6. Ester Formation:

• 4C₆H₁₂H₆ + 3(CH₃CO)₂O —catalyst, t degree—-> C₆H₇O(OCOCH₃)₅

• Note: This reaction shows that glucose has 5 -OH groups that can form esters with acetic acid.

7. Glucose Synthesis:

• Starch Hydrolysis: (C₆H₁₀O₅)_n + nH₂O —H+, t degree —-> nC₆H₁₂O₆

• Cellulose Hydrolysis: (C₆H₁₀O₅)_n + nH₂O —concentrated HCl —-> nC₆H₁₂O₆

8. Structure of Glucose:

• Open-chain structure: CH₂OH[CHOH]₄CHO

• Note: Glucose is a polyfunctional compound, with an aldehyde group and five hydroxyl groups in its open-chain form. It exists in both open-chain and cyclic forms.

9. Other Names:

• Dextrose, blood sugar

10. Properties:

• Glucose exhibits aldehyde properties, as seen in the silver mirror test.

• Glucose is a nutrient, used as an energy booster.

• Glucose is converted from sucrose for use in silvering mirrors, coating thermos bottles, and as an intermediate in the production of ethanol.

Fructose (C₆H₁₂O₆)

1. Properties:

• Fructose is a crystalline, colorless substance, readily soluble in water, and sweeter than sucrose.

• Fructose is found in abundance in sweet fruits like pineapple, mango, etc.

• Fructose does not react with Br₂ and does not undergo alcoholic fermentation.

2. Conversion:

• Fructose ___OH-___> Glucose

3. Structure:

• Open-chain structure: CH₂OH[CHOH]₃-CO-CH₂OH

4. Note:

• Fructose is a structural isomer of glucose. It is a ketose, having a ketone group in its open-chain structure.

5. Molecular Weights:

• C₆H₁₂O₆ (glucose): 180

• C₁₂H₂₂O₁₁ (sucrose): 342

• (C₆H₁₀O₅)_n (starch): 162n

General Notes:

• Carbohydrates are organic compounds primarily composed of carbon, hydrogen, and oxygen.

• Carbohydrates play crucial roles in living organisms, serving as energy sources, structural components of cells, and more.

• Carbohydrates are classified based on their structure and chemical properties.

• Glucose and fructose are common monosaccharides, playing vital roles in nutrition and biochemistry.

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