Question

why glucose does not show 2,4DNP test?

Answer 1

hloo dear...

This happens because the glucose actually exists in the cyclic hemiacetal form with only a small amount of the open chain form in equilibrium.

Answer 2

Hell.. oo!!

That was fault with linear chain structure of glicose....though CHO group is free ..it doesnt react with schiffs reagent ......

therefore to over come the fallacy ...they then found that glucose doesnt have linear chain  structure....but has a cylic structure in which CHO group is not free...that is it is bonded with 5th OH group

hope this helps you