Question:
Which of the following pairs give positive Tollens' test?
Which of the following pairs give positive Tollens' test?
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Fructose gives positive Tollens' test because it isomerizes to glucose under basic conditions.
Updated On: Apr 20, 2026
- Glucose, sucrose
- Glucose, fructose
- Hexanal, acetophenone
- Fructose, sucrose
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Tollens' test is positive for aldehydes and $\alpha$-hydroxy ketones (which can tautomerize to aldehydes).
Step 2: Detailed Explanation:
Glucose (aldehyde) gives positive Tollens'. Fructose ($\alpha$-hydroxy ketone) tautomerizes to glucose and gives positive Tollens'. Sucrose (no free aldehyde or $\alpha$-hydroxy ketone) gives negative. Acetophenone (aromatic ketone) gives negative. Hexanal (aldehyde) gives positive. So pair (B) both give positive.
Step 3: Final Answer:
Glucose, fructose
Tollens' test is positive for aldehydes and $\alpha$-hydroxy ketones (which can tautomerize to aldehydes).
Step 2: Detailed Explanation:
Glucose (aldehyde) gives positive Tollens'. Fructose ($\alpha$-hydroxy ketone) tautomerizes to glucose and gives positive Tollens'. Sucrose (no free aldehyde or $\alpha$-hydroxy ketone) gives negative. Acetophenone (aromatic ketone) gives negative. Hexanal (aldehyde) gives positive. So pair (B) both give positive.
Step 3: Final Answer:
Glucose, fructose
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