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Which one of the following is NOT correc...

Which one of the following is NOT correct for monosaccharides?
1. They are optically active polyhydroxy carbonyl compounds
2.Fructose is ketose sugar and hence it does not give red precipitate with Fehling solution
3. `alpha - D(+)` glucose and `beta - D(+)` glucose are anomers
4. Glucose and mannose are anomers

A

1,2,3

B

2,3

C

2,4

D

4

Text Solution

AI Generated Solution

The correct Answer is:
To solve the question, we need to identify which statement about monosaccharides is NOT correct. Let's analyze each option step by step. ### Step 1: Analyze Option 1 **Statement:** "They are optically active polyhydroxy carbonyl compounds." - **Explanation:** Monosaccharides are indeed optically active because they contain one or more chiral centers. They are polyhydroxy because they have multiple hydroxyl (–OH) groups, and they contain a carbonyl group (either aldehyde or ketone). Therefore, this statement is **correct**. **Hint:** Check if the compound has chiral centers and functional groups that define its classification. ### Step 2: Analyze Option 2 **Statement:** "Fructose is a ketose sugar and hence it does not give red precipitate with Fehling solution." - **Explanation:** Fructose is a ketose sugar, but it can isomerize to glucose and mannose in the presence of Fehling's solution, which allows it to give a red precipitate. Therefore, this statement is **incorrect**. **Hint:** Consider the reactivity of sugars in Fehling's test and the ability of ketoses to isomerize. ### Step 3: Analyze Option 3 **Statement:** "Alpha-D(+) glucose and beta-D(+) glucose are anomers." - **Explanation:** Anomers are a type of stereoisomer that differ at the anomeric carbon (the carbon that was the carbonyl carbon in the open-chain form). Alpha-D-glucose and beta-D-glucose differ in the configuration at the first carbon, making this statement **correct**. **Hint:** Recall the definition of anomers and identify the anomeric carbon in cyclic forms. ### Step 4: Analyze Option 4 **Statement:** "Glucose and mannose are anomers." - **Explanation:** Glucose and mannose are not anomers; they are epimers because they differ at the second carbon (C2), not at the anomeric carbon (C1). Therefore, this statement is **incorrect**. **Hint:** Differentiate between anomers and epimers based on the carbon atoms they differ at. ### Conclusion From the analysis: - Option 1 is correct. - Option 2 is incorrect. - Option 3 is correct. - Option 4 is incorrect. The statements that are NOT correct for monosaccharides are options 2 and 4. However, since the question asks for one option that is NOT correct, the best answer is **Option 2**. ### Final Answer: **Option 2: Fructose is a ketose sugar and hence it does not give red precipitate with Fehling solution.**
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