Question

What reduction reactions can be used to identify the configuration of sugars?

Answer 1

Hint: The endpoints of the resulting alditol chain are identical when aldoses are reduced with sodium borohydride, \[HOC{H_2}(CHOH)nC{H_2}OH\]. After such a reduction, different (diastereomeric) sugars give the same alditols. As a result of the reduction of allose and galactose, allitol and galactitol are achiral. The chiral alditol of altrose and talose is the same.

Complete answer:
It should be noted that osazone formation can also be used to determine sugar arrangement. The osazone formation process is utilized to distinguish aldose sugars with only a -carbon configuration difference. Bis-phenylhydrazine, also known as an osazone, is made up of three phenylhydrazine molecules. D-glucose and D-mannose osazones are identical, showing that the sole difference is in their C-2 structure.
Osazone formation was developed by Emil Fischer, who used the reaction as a test to identify monosaccharides. The formation of a pair of hydrazone functionalities involves both oxidation and condensation reactions. Since the reaction requires a free carbonyl group, only "reducing sugars" participate. Sucrose, which is nonreducing, does not form an osazone. After such − \[(CHOH)\] the group is oxidized. Thus, we can here say that the aldose and ketose have the same osazone since they have the same structure in all carbons except the C1 and C2. For example, the glucose and fructose from the glucosazone, and fructosazone have a similar structure. While the mechanism of the phenylhydrazone formation is a straightforward addition of phenylhydrazine to a carbonyl group with noncommitment elimination of water, the osazone formation has been formulated by several mechanisms.

Note:
So, from the structures of the osazones formed by glucose, galactose, fructose and mannose, we can say that osazones of glucose, mannose and fructose are same and osazone formed by Galactose is different at stereochemistry at 4th carbon.