Glucose is classified as which type of sugar?

• A. Aldopentose
• B. Ketopentose
• C. Aldohexose
• D. Ketohexose

Answer: (C)

Glucose is classified by two features: the number of carbon atoms and the type of carbonyl group in its open-chain form. It has six carbons, so it’s a hexose. The functional group at the carbonyl position is an aldehyde, not a ketone, so it’s an aldose. Put together, that makes it an aldohexose.

This distinguishes it from an aldopentose (five carbons with an aldehyde), a ketopentose (five carbons with a ketone), or a ketohexose (six carbons with a ketone, like fructose). In solution, glucose may cyclize, but its classification stays as an aldose and hexose.