NURSING ANM AND GNM

Detailed explanation-1: -Fehling’s reagent is commonly used for reducing sugars but is known to be not specific for aldehydes. For example, fructose gives a positive test with Fehling’s solution too, because fructose is converted to glucose and mannose under alkaline conditions.

Detailed explanation-2: -Thus, although the ketose fructose is not strictly a reducing sugar, it is an alpha-hydroxy-ketone and gives a positive test because the base in the reagent converts it into the aldoses glucose and mannose.

Detailed explanation-3: -In basic medium, fructose show keto-enol tautomerism and thus isomerises to glucose due to which it gives positive Tollen’s and Fehling’s reagent test.

Detailed explanation-4: -Alpha hydroxy ketones give positive test with Fehling’s solution. Because Alpha hydroxy ketone gets converted into aldehyde by tautomerism . Aldehyde gives positive test with Fehling’s solution whereas ketones don’t give positive test with it.