First slide

Fructose

Question

From the following compounds how many can give positive Fehling's test
A) Sucrose
B) Benzaldehyde
C) Fructose
D) Formic acid

Moderate

A

A, D only
B

B, C, D only
C

C, D only
D

B only

Solution

Sucrose …disaccharide….no free anomeric -OH groups….cannot give positive Fehling's test.
Benzaldehye…aromatic aldehyde…cannot give positive Fehling's test.
Fructose…monosaccharide…even though it is a ketose it can give positive Fehling's test due to reversible isomerisation in alkaline medium.
Formicacid…contains -CHO group…can give positive Fehling's test.

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