question_answer

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

E)  D-glucose, D-galactose and D-talose

Correct Answer: B

Solution :

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 \[\underset{\begin{align}   & | \\  & {{(CHOH)}_{3}} \\  & | \\  & C{{H}_{2}}OH \\ \end{align}}{\overset{\begin{smallmatrix}  CH=NNH{{C}_{6}}{{H}_{5}} \\  | \end{smallmatrix}}{\mathop{C=NNH{{C}_{6}}{{H}_{5}}}}}\,\]