Question

Which of the following hexoses will form the same osazone when treated with excess phenyl-hydrazine?

• A. $D$-glucose, $D$-fructose and $D$-galactose
• B. $D$-glucose, $D$-fructose and $D$-mannose
• C. $D$-glucose, $D$-mannose and $D$-galactose
• D. $D$-fructose, $D$-mannose and $D$-galactose

Answer 1

Answer: (B)

$D$-glucose, $D$-fructose and $D$-mannose

Answer 2

D-glucose, D-fructose and D-mannose form the same osazone treated with excess phenyl hydrazine because they differ only 1st and 2nd carbon atoms which are transformed to the same form.
They form same osazone $\underset{\begin{aligned} & | \\\ & {{(CHOH)}_{3}} \\\ & | \\\ & C{{H}_{2}}OH \\\ \end{aligned}}{\overset{\begin{smallmatrix} CH=NNH{{C}_{6}}{{H}_{5}} \\\ | \end{smallmatrix}}{\mathop{C=NNH{{C}_{6}}{{H}_{5}}}}}\,$