BIOMOLECULES AND ENZYMES

Detailed explanation-1: -Glucose contains an aldehyde group in its open structure but forms a cyclic acetal structure(also called pyranose). This structure is quite stable and is not broken down by Schiff’s reagent which is a weak base.

Detailed explanation-2: -Glucose does not answer Schiff’s test and NaHSO3 test due to absence of aliphatic aldehydes in the ring structure and absence of free aldehydic group.

Detailed explanation-3: -Organic chemists have, of course, used Schiff s reagent for many years as a qualitative test for the presence of aldehydes. A positive test is indicated by a change from pale yellow (colourless) to deep red-violet upon addition of the aldehyde to the rea-gent.

Detailed explanation-4: -Therefore, hydrazone does not shape, giving a negative Schiff’s test.

Detailed explanation-5: -Glucose does not react with Schiff’s reagent and 2, 4 DNP reagent although it has an aldehydic group. You can see that OH at 5-carbon reacts with the aldehyde group at 1 carbon to form hemiacetal in a cyclic form.