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JEE Main 2025 · Chemistry · Biomolecules and Polymers · medium

D-Glucose, D-mannose, D-fructose and D-galactose are each heated separately with excess phenylhydrazine. The number of different osazones obtained is

Single correct option

D-Glucose, D-mannose, D-fructose and D-galactose are each heated separately with excess phenylhydrazine. The number of different osazones obtained is
  1. A. 11
  2. B. 22
  3. C. 33
  4. D. 44
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Answer: (B) 22

Osazone formation involves only C1\mathrm{C_1} and C2\mathrm{C_2} (the carbonyl carbon and its neighbour); the configuration at C2 is destroyed. D-Glucose, D-mannose (C2 epimers) and D-fructose (same C3-C6 configuration) therefore give the identical glucosazone. D-Galactose differs at C4, so it gives a different osazone. Hence 22 distinct osazones.
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