Question

In which of the following pairs at least one of the compounds give positive Tollens test?

• A. Glucose and sucrose
• B. Glucose and fructose
• C. Fructose and sucrose
• D. Maltose and sucrose

Answer 1

Answer: (A), (B), (C), (D)

Maltose and sucrose

Glucose, Fructose, Maltose are reducing sugars.

Example: Glucose is a reducing sugar as it has a free aldehyde group. Fructose does not have any aldehydic group still it can isomerise into glucose and mannose (by keto-enol tautomerism because of the presence of alpha-hydroxy ketone) in the alkaline medium therefore giving a positive test with Tollens' reagent and therefore acts as a reducing sugar. However, Sucrose, a disaccharide does not react with Tollen's reagent thereby acting as a non-reducing sugar because of the lack of free carbonyl group.