why glucose doesnot react with schiff's reagent and 2,4 DNP though it has -CHO (Aldehyde) group?
Glucose does not react with Schiff's reagent and 2,4 DNP reagent although it has an aldehydic group. You can see in the figure given below that OH at 5 - carbon react with aldehyde group at 1 carbon to form hemiacetal in a cyclic form. After the internal cyclisation, it forms either α- anomer or β-anomer. In these forms free aldehydic group is not present. So, it does not give the reaction of aldehydic group.