Number of compounds from the following which will not produce orange red precipitate with Benedict solution is ____________
Glucose, maltose, sucrose, ribose, 2-deoxyribose, amylose, lactose
Glucose, maltose, sucrose, ribose, 2-deoxyribose, amylose, lactose
Correct Answer: 3
Solution and Explanation
Benedict’s solution is used to test for the presence of reducing sugars. Reducing sugars are carbohydrates that have a free aldehyde or ketone group capable of reducing \( \text{Cu}^{2+} \) ions in Benedict’s solution to \( \text{Cu}^+ \), resulting in the formation of an orange-red precipitate of copper(I) oxide (\( \text{Cu}_2\text{O} \)).
Analysis of the Given Compounds:
- Glucose: Reducing sugar (✓) — Has a free aldehyde group.
- Maltose: Reducing sugar (✓) — Contains a free reducing end from glucose units.
- Sucrose: Non-reducing sugar (×) — The glucose and fructose units are linked by their anomeric carbons, leaving no free aldehyde or ketone group.
- Ribose: Reducing sugar (✓) — Has a free aldehyde group.
- 2-Deoxyribose: Reducing sugar (✓) — Has a free aldehyde group.
- Amylose: Non-reducing sugar (×) — Does not have a free aldehyde group accessible for reduction.
- Lactose: Reducing sugar (✓) — Contains a free reducing end from glucose units.
Compounds That Do Not React:
The two compounds that do not give a positive Benedict’s test are:
- Sucrose: Due to the linkage of glucose and fructose at their anomeric carbons, it lacks a free aldehyde or ketone group.
- Amylose: Does not have a free aldehyde group to react with Benedict’s reagent.
Final Answer:
Two compounds (sucrose and amylose) will not produce an orange-red precipitate with Benedict’s solution.
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