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BIO NMDCAT Carbohydrates
nmdcat.online June 27, 2026

The Osazone test is a chemical test for reducing sugars that involves the reaction of phenylhydrazine with the carbonyl group. In this reaction, glucose and fructose form identical needle-shaped osazone crystals because

A. They are structural isomers that are epimerized under the reaction conditions
B. The reaction only engages the first two carbon atoms, forming the same derivative from both sugars
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C. Fructose is first converted to glucose by the phenylhydrazine
D. Both sugars form a furanose ring structure under the reaction conditions

📝 Explanation

The osazone formation involves C-1 and C-2 of a reducing sugar. Glucose and fructose differ only in the configuration at C-1 and C-2 (glucose is an aldose, fructose is a ketose). The reaction eliminates these differences, forming an identical phenylosazone. The rest of the carbon skeleton is identical.

📖 Additional Information

  • They are structural isomers that are epimerized under the reaction conditions
  • The reaction only engages the first two carbon atoms, forming the same derivative from both sugars
  • Fructose is first converted to glucose by the phenylhydrazine
  • Both sugars form a furanose ring structure under the reaction conditions

The osazone formation involves C-1 and C-2 of a reducing sugar. Glucose and fructose differ only in the configuration at C-1 and C-2 (glucose is an aldose, fructose is a ketose). The reaction eliminates these differences, forming an identical phenylosazone. The rest of the carbon skeleton is identical.

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