JEE Main levelSingle correct optionDifficulty 2 of 3bm015
D-Glucose, D-mannose and D-fructose all give the same osazone with excess phenylhydrazine because
Aall three sugars are aldoses
Ball three sugars exist as pyranoses
Cthe osazone retains the C-2 stereocentre, which is the same in all three
DC-1 and C-2 become C=N-NHPh groups so the C-2 stereocentre is lost, and C-3, C-4 and C-5 have the same configuration in all three sugars
Answer: D
Osazone formation takes place at C-1 and C-2 only, destroying the C-2 stereocentre. Glucose, mannose (C-2 epimer) and fructose have identical C-3, C-4 and C-5, so one osazone results.