Fructose Structure

Fructose is a simple ketonic monosaccharide present in many plants, it is also known as fruit sugar. In plants, it is often bonded to glucose to form the disaccharide sucrose. It is absorbed directly in the bloodstream during the digestion.

A French chemist named Augustin-Pierre Dubrunfaut first discovered fructose in the year 1847. Later, in the year 1857, the term was officially coined by an English chemist named William Allen Miller.

Other Names Fruit sugar, levulose, d-fructofuranose, d-fructose, d-arabino-hexulose
Chemical Formula C6H12O6
Molar Mass 180.156 g·mol−1
Density 1.694 g/cm3
Melting Point 103 °C (217 °F; 376 K)
Water Solubility ~4000 g/L (25 °C)

Some of the key characteristics of fructose are; when it is pure and dried it is white in colour, it is odourless, tastes sweet, and has a crystalline form. It is the most water-soluble among all the different types of sugars. The fructose sugar is usually found naturally in fruits, flowers, trees, honey, berries and in rooted vegetables.

As for the chemical properties, fructose is a monosaccharide and also a reducing sugar. The older name of fructose was levulose as it rotated the plane-polarized light in the left direction. This was the sole reason that it was classified as a laevorotatory compound. Whereas, glucose rotates the plane-polarized light in the right direction and is thus categorized as a dextrorotatory compound.

Fructose Structure

An interesting fact: bees collect nectar from the flowers which consist of sucrose. Then they use an enzyme to hydrolyze or break apart the sucrose into its component parts of the glucose and fructose.

Also Read: Fructose

Structure of Fructose

Fructose has a cyclic or chair-like structure. The chair form of fructose is similar to that of glucose but in the structure of fructose, there are few exceptions. Fructose has a ketone functional group and the ring closure occurs from 2nd carbon position. This result in the rise to 5-membered ring or there is a formation of intramolecular hemiacetal in fructose. The OH at 5th carbon combines with carbon in the 2nd position.

The five-membered ring has four carbons and one oxygen. There is basically a formation of chiral carbon and two arrangements of CH2OH and OH group. In essence, fructose displays stereoisomerism.

Ring Structure of D-Fructose

 

Steps In The Ring Closure (Hemiketal Synthesis)

  • The electrons present on the alcohol oxygen are used to bond the carbon at 2nd position to form an ether.
  • The hydrogen is transferred to the carbonyl oxygen to form a new OH bond which further provides a ring to the keto structure of fructose.

Hemiketal Synthesis

Hemiketal Functional Group

The carbon which is the centre of hemiketal functional group is referred to as anomeric carbon. Hemiketal group has both an ether oxygen and an alcohol group which is attached to two other carbons.

Comparison Of Alpha And Beta Structure Of Fructose

If the alcoholic group (OH) is present on the same side of the ring as the carbon at 6 then it is Beta structure. The cyclic ring structure leads to an upward projection of the alcoholic (OH) group at carbon 2. If the –OH is present on the opposite side of the ring as the carbon at 6 then the ring structure leads to a downward projection of OH at carbon.

Alpha - Glucose and Alpha - Fructose

Compare Glucose And Fructose In The Chair Structures

The fructose is identified as a five-membered ring having six-carbon, a hexose whereas glucose is a six-membered ring with –OH group on the carbon at 4th position in a down projection.

Molecular and Structure Formula Of Fructose

Fructose is a levorotatory monosaccharide which means it rotates the plane-polarized light in the left direction. The chemical composition of fructose is C6H12O6 but shows different bonding from glucose. Fructose is a hexose however it exists as a 5-member hemiketal ring. The hemiketal ring helps for a long metabolic pathway and high reactivity in comparison to glucose.

Isomerism

The configuration of D-Fructose is similar in its penultimate carbon as D-glyceraldehyde. Due to the stereometric structure, fructose is much sweeter than glucose.

Configuration of D-Fructose

Properties Of Fructose

  • The fructose is a white crystalline compound.
  • It melts at a temperature of 102⁰C.
  • Fructose absorbs moisture rapidly and loses it slowly to form hydroxymethylfurfural into the environment in comparison to other sugars.
  • It can be fermented anaerobically using yeast or bacteria by which they are converted into ethanol and carbon dioxide.

Properties Of Fructose

Comparison Of Fructose And Glucose In Brief

PROPERTY FRUCTOSE GLUCOSE
Molecular Formula C6H12O6 C6H12O6
Nature Polyhydroxy ketone Polyhydroxy aldehyde
Melting Point 102⁰C 146⁰C
Optical activity of natural form Laevorotatory Dextrorotatory
With ethyl alcohol More soluble Almost insoluble
Reduction Mixture of sorbitol and mannitol Sorbitol
Molichs Reagent Forms a violet ring Forms a violet ring
Fehlings Solution Gives red precipitate Gives red precipitate
Tollens reagent Forms silver mirror Forms silver mirror
Phenyl Hydrazine Forms Osazone Forms osazone
Oxidation with bromine water No reaction Gluconic acid
Oxidation with nitric acid Mixture of glycollic acid, tartaric acid and tri hydroxyl glutaric acid Saccharic acid
Alchoholic a-naphthol+HCL conc. A purple colour on boiling No colouration

Comparison Of Fructose And sucrose In Brief

Fructose Sucrose
Monosaccharide Disaccharide
Fructose combine with sucrose to form sucrose Fructose combine with sucrose to form sucrose
Chemical formula – C6H12O6. Chemical formula – C12H22O11.
Molecular weight – 180.16 g/mol Molecular weight – 342.2965 g/mol
Reducing sugar Non-reducing sugar
Melting Point – 03°C (217.40°F) Melting Point – 186°C (366.80°F)
Boiling point – 440°C (824°F) Boiling point – 669.431 °C
Density: 1.69 g/cm³ Density : 1.59 g/cm³

Uses of Fructose

Some common uses of Fructose are:

  • It helps in enhancing the taste in food and beverages.
  • Crystalline fructose (natural sweetener) used in energy drinks, chocolate milk, cereals, and yogurts and many other beverages and low-calorie foods.
  • HFCS ( High Fructose Corn Syrup) products is a combination of glucose and fructose.
  • High fructose corn syrup is also used as a sweetener in many children and adult medicines such as cough suppressants and decongestant liquids.

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