Question

Which of the following pairs give positive Tollen's s test?

• A. Glucose, sucrose
• B. Glucose, fructose
• C. Hexaual, acetophenone
• D. Fructose, sucrose

Answer 1

The correct option is B Glucose, fructose

Aldehydes and alpha hydroxy ketones give positive Tollen’s test. Glucose has an aldehydic group and fructose is an alpha hydroxy ketone.

Only aldehyde give positive Tollen's test. However, under the strongly basic condition of the test $\alpha -$hydroxy ketones can isomerize to aldehydes (i.e. endiol rearrangement in fructose that inter convert ketones to aldoses.) so that's why will also gives a positive Tollen's test $\alpha -$ hydroxy ketones.