All about Osazone

All about Osazone

Let us look into this problem:

Consider the following reaction,

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Among the following compounds, whose osazone derivative will have same mp as that of X ?

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Answer:

To answer this question we first need to know what Osazone is. Osazone is formed when Aldose and Ketose react with excess phenyl hydrazine.

Reaction with aldose:

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Reaction with ketose:

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So as we can see, both aldose and ketose react with 3 equivalent of phenyl hydrazine to give osazone. And the stereochemistry of osazone depends on the configuration of C-3 to C-6 and not on C-1 and C-2. Thus D-glucose and D-fructose give same osazone when react with 3 equivalent of phenyl hydrazine.

Now if we look at the question given the osazones which we will get are:

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So as we can see, osazones b & c are same as X (osazone from D-glucose). Whereas osazone a is the enantiomer of X. Now mp is a physical property so enantiomers will have same mp So osazones of a, b & c will have same mp as that of X.