Monosaccharides: Fructose
Structure of fructose (ketohexose), including its open-chain and cyclic forms, and comparison with glucose.
What is Monosaccharides: Fructose?
A monosaccharide containing six carbon atoms and a ketone functional group.
Key formula / rule: Fructose Molecular Formula
Key points
- Identify fructose as a ketohexose.
- Draw the open-chain structure of fructose.
- Explain the formation of cyclic furanose and pyranose structures.
- Differentiate between the open-chain and cyclic forms of fructose.
Common exam trap
Confusing fructose with glucose (aldose vs. ketose).
Definitions
- Term
Ketohexose
- Meaning
A monosaccharide containing six carbon atoms and a ketone functional group.
- Term
Furanose
- Meaning
A cyclic form of a monosaccharide containing a five-membered ring, including one oxygen atom.
- Term
Pyranose
- Meaning
A cyclic form of a monosaccharide containing a six-membered ring, including one oxygen atom.
- Term
Reducing Sugar
- Meaning
A sugar that can act as a reducing agent because it has a free aldehyde or ketone group, or can tautomerize to form one.
Learning objectives
Identify fructose as a ketohexose.
Draw the open-chain structure of fructose.
Explain the formation of cyclic furanose and pyranose structures.
Differentiate between the open-chain and cyclic forms of fructose.
Understand why fructose is a reducing sugar.
Formulae
- Name
Fructose Molecular Formula
- Note
Same as glucose, but different structure.
- Expression
C6H12O6
Prerequisites
Basic organic chemistry nomenclature (alcohols, ketones).
Understanding of functional groups.
Concept of chirality and optical isomerism.
Basic understanding of carbohydrates (monosaccharides, hexoses).
Common mistakes
Confusing fructose with glucose (aldose vs. ketose).
Forgetting that fructose also exists in cyclic forms (furanose and pyranose).
Assuming fructose is a non-reducing sugar due to the ketone group (it is reducing because it can tautomerize to the open-chain form).
Incorrectly drawing the cyclic structures without proper hemiacetal formation.
Keywords
Fructose
Ketohexose
Fruit sugar
Levulose
Monosaccharide
Carbohydrate
Furanose
Pyranose
Reducing sugar
Cyclic structure
Open-chain structure
Practice preview
Fructose is a type of carbohydrate. What is its classification based on its functional group?…
easy
The open-chain structure of fructose is characterized by which of the following arrangements of functional groups?…
easy
When fructose is treated with bromine water, it does NOT give a positive test for an aldehyde. This observation supports which of the following conclusions about fructose?…
medium