Fructose vs Glucose vs Sucrose: Key Differences with Table
Fructose is essential in chemistry and helps students understand various practical and theoretical applications related to this topic. It often appears in exam questions and is a key example within carbohydrates and food chemistry.
What is Fructose in Chemistry?
A fructose is a simple sugar or monosaccharide found commonly in fruits, honey, and some vegetables. In chemistry, fructose is classified as a ketohexose due to its six-carbon structure and a ketone functional group present at the C2 position.
This concept appears in chapters related to Monosaccharides, Carbohydrates, and Carbohydrate Classification and Structure, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
The molecular formula of fructose is C6H12O6. It consists of six carbon atoms, twelve hydrogen atoms, and six oxygen atoms, and is categorized under monosaccharide carbohydrates called 'hexoses.' As a ketohexose, fructose contains a ketone group on the second carbon, distinguishing it from glucose, which has an aldehyde group.
Preparation and Synthesis Methods
Fructose can be prepared in the laboratory by hydrolyzing sucrose (common table sugar) using dilute acids or the enzyme invertase. The reaction splits sucrose into an equimolar mixture of glucose and fructose.
Industrially, high-fructose corn syrup is made by enzymatically converting glucose from corn starch to fructose using glucose isomerase. In plants, fructose is naturally produced during photosynthesis and carbohydrate metabolism.
Physical Properties of Fructose
Fructose is a white, crystalline solid at room temperature. It is the most water-soluble sugar, with a sweet taste (about 1.7 times sweeter than sucrose) and a melting point around 103°C.
Fructose is odorless but has a sticky, highly hygroscopic texture, meaning it likes to absorb moisture from the air. Its molar mass is 180.16 g/mol, and it is highly soluble in water but almost insoluble in nonpolar solvents.
Chemical Properties and Reactions
Fructose exhibits several important chemical properties:
- It acts as a reducing sugar and gives positive results with Benedict’s and Fehling’s tests.
- Fructose shows mutarotation and can exist in open-chain (linear) and cyclic (ring) forms—mostly as fructofuranose (five-membered ring) and as fructopyranose (six-membered ring).
- It undergoes fermentation by yeast to produce ethanol and carbon dioxide.
- It participates quickly in the Maillard reaction during cooking, leading to browning and flavor development in baked goods.
- It reacts with strong acids to form hydroxymethylfurfural (HMF), which has industrial applications.
Frequent Related Errors
- Confusing fructose with glucose or sucrose based on formula alone.
- Misidentifying the functional group (ketone vs. aldehyde) in structural questions.
- Assuming all sugars react the same way in chemical tests (e.g., not all are reducing sugars—sucrose is not, but fructose is).
Uses of Fructose in Real Life
Fructose is widely used as a natural sweetener in foods, especially in fruit juices, soft drinks, jams, and confectionery. High-fructose corn syrup is a major component of sweetened beverages and baked goods.
It is also used in diet foods for diabetics due to its moderate effect on blood sugar and is an ingredient in nutritional bars and infant formulas. Industrial applications include production of diesel fuel additives and specialty plastics.
Relation with Other Chemistry Concepts
Fructose is closely related to topics such as Sucrose hydrolysis and Glycolysis, where it is metabolized for cellular energy. It also demonstrates isomerism with glucose and is a practical example of reducing sugars covered in Reducing and Non Reducing Sugars.
Step-by-Step Reaction Example
- Hydrolysis of Sucrose:
C12H22O11 (sucrose) + H2O → C6H12O6 (glucose) + C6H12O6 (fructose)
- Condition: Use dilute H2SO4 or invertase enzyme.
Heated under controlled temperature for efficient conversion.
Lab or Experimental Tips
Remember fructose as the “fruit sugar”—it tastes very sweet and gives a positive Benedict’s or Fehling’s test only after base-catalyzed tautomerization. Vedantu educators often use the “Fruity Five” tip: fructose typically forms a stable five-membered ring (furanose) in solution—helpful for structure drawing in exams.
Try This Yourself
- Write the IUPAC name of fructose.
- Draw Fischer and Haworth projections for fructose.
- List two food products rich in fructose.
Final Wrap-Up
We explored fructose—its important structure, physical and chemical properties, main synthesis methods, uses, and related chemistry. For more in-depth explanations and exam-prep tips related to fructose, join live classes and access revision notes on Vedantu.
FAQs on Fructose: Structure, Properties, and Importance in Chemistry
1. What is fructose and where is it found?
Fructose is a simple sugar (monosaccharide) found naturally in many foods.
• It commonly occurs in fruits, honey, and certain vegetables.
• Fructose is also known as "fruit sugar."
• It is widely used as a sweetener in the food industry.
2. Is fructose a reducing sugar?
Yes, fructose is a reducing sugar.
• It has a free ketone group in its open-chain form.
• Fructose gives a positive result with Benedict’s and Fehling’s tests.
• This property helps distinguish it from non-reducing sugars.
3. What is the formula and structure of fructose?
The molecular formula of fructose is C6H12O6.
• Fructose is a ketohexose monosaccharide.
• It can exist in both open-chain and cyclic (furanose) forms.
• The cyclic structure is often shown as a five-membered ring in Haworth projections.
4. How is fructose different from glucose?
Fructose and glucose have the same molecular formula but differ in structure and function.
• Fructose is a ketohexose; glucose is an aldohexose.
• Both are reducing sugars but react differently due to their structures.
• Fructose is found mostly in fruits; glucose is common in both plants and animals.
5. What are the key physical properties of fructose?
Fructose is a colorless, crystalline solid.
• It is highly soluble in water.
• It has a very sweet taste (sweeter than sucrose or glucose).
• Fructose melts at about 103°C.
6. What are the main food sources of fructose?
Major sources of fructose include:
• Fruits such as apples, pears, mangoes, and grapes.
• Honey
• Some vegetables (e.g., sweet corn)
• Processed foods (high-fructose corn syrup is commonly added to soft drinks and snacks)
7. What is fructose intolerance and what are its symptoms?
Fructose intolerance is a metabolic disorder where the body cannot digest fructose properly.
Symptoms may include:
• Bloating
• Abdominal pain
• Diarrhea
• Nausea after consuming fructose-rich foods
• In severe cases, liver and kidney issues
8. How is fructose prepared in the laboratory?
Fructose can be prepared by:
1. Hydrolysis of sucrose (cane sugar): Sucrose reacts with water in the presence of acid or enzyme to yield fructose and glucose.
2. Hydrolysis of inulin: Inulin found in plants like dahlia and chicory is hydrolyzed to obtain fructose.
Both methods are important in industrial and laboratory settings.
9. What is the role of fructose in human metabolism?
Fructose plays an energetic role in metabolism.
• It is absorbed in the small intestine and transported to the liver.
• In the liver, fructose is converted into glucose or directly enters glycolysis after conversion to fructose-1-phosphate.
• Excessive fructose consumption can affect liver health.
10. How does fructose compare with sucrose?
Fructose vs. Sucrose:
• Fructose is a monosaccharide; sucrose is a disaccharide (glucose + fructose).
• Sucrose must be hydrolyzed to produce fructose before absorption.
• Fructose is sweeter than sucrose.
• Both are found in fruits, but sucrose is also widely used as table sugar.
11. Why is fructose considered sweeter than other sugars?
Fructose has the highest sweetness among common dietary sugars.
• It interacts more efficiently with taste receptors.
• Its structure allows stronger binding, resulting in a perceived higher sweetness than glucose or sucrose.
12. Can fructose be converted into glucose in the body?
Yes, fructose can be converted into glucose.
• In the liver, enzymes enable fructose to undergo isomerization.
• This process helps supply glucose for energy when needed.
