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How do glucose and fructose differ in their chemical groups?

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Tall, dense stalks of sugarcane grow on both sides of a narrow path, with green leaves arching overhead and sunlight illuminating the plants. — sugar Lines of sugarcane before harvest.

Although glucose and fructose share the same molecular formula, $C_{6} H_{12} O_{6}$ , they are isomers that differ in their structural arrangements and chemically reactive groups.1

The primary difference lies in their functional groups:

Glucose is an aldohexose, meaning it contains an aldehyde group ( $—CHO$ ) typically located at the first carbon atom.12
Fructose is a ketohexose, meaning it contains a ketone group ( $—C=O$ ) typically located at the second carbon atom.12

In aqueous solutions, these sugars often form cyclic structures. Glucose forms a cyclic hemiacetal by reacting its hydroxyl group with the aldehyde group at position 1, while fructose forms a cyclic hemiketal by reacting its hydroxyl group with the ketone group at position 2. These structural distinctions are fundamental to their unique chemical properties and biological roles.231