Question

Which of the following carbohydrates will give the same osazone?

• A. Glucose
• B. Fructose
• C. Cane sugar
• D. Lactose

Answer 1

Answer: (A), (B)

The correct options are
A

Glucose

B

Fructose

Osazones are formed when reducing sugars are treated with phenylhydrazine. This method is used to identify sugars whose stereochemistries differ by one chiral centre.

Osazones are coloured crystalline compounds and each sugar has a characteristic osazone formed on reaction with phenylhydrazine.

For instance, Lactose forms powder puff shaped crystals, Maltose forms petal shaped crystals and Galactose forms rhombic plate shaped crystals.

Glucose and fructose differ by only two carbons at $C_1$ and $C_2$ and forms needle shaped crystals. This is because, these two compounds on reaction with phenylhydrazine form hydrazoles with no structural differences.