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 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.

 

 

 

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Because glucose's aldehyde group is not free.. its aldehyde group is bonded to the -OH group of 5th carbon atom.

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 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

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