Cyclic Structure of Fructose Notes | Study Chemistry for JEE - JEE

JEE: Cyclic Structure of Fructose Notes | Study Chemistry for JEE - JEE

The document Cyclic Structure of Fructose Notes | Study Chemistry for JEE - JEE is a part of the JEE Course Chemistry for JEE.
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Cyclic structure of Fructose:

Like glucose, fructose also has a cyclic structure. Since fructose contains a keto group, it forms an intramolecular hemiketal. In the hemiketal formation, C5-OH of the fructose combines with C2-keto group. As a result, C2 becomes chiral and thus has two possible arrangements of CH2OH and OH group around it. Thus,

Cyclic Structure of Fructose Notes | Study Chemistry for JEE - JEE

D-fructose exists in two stereoisomeric forms, i.e., α-D-fructopyranose and β-D fructopyranose. However in the combined state (such as sucrose), fructose exists in furanose form as shown below:



Cyclic Structure of Fructose Notes | Study Chemistry for JEE - JEE

 

Hydroylsis of Sucrose:

Cyclic Structure of Fructose Notes | Study Chemistry for JEE - JEE

(Invert Sugar or Invertose). Hydrolysis of sucrose with hot dilute acid yields D-glucose and D-fructose.

C12H22O11 + H2O Cyclic Structure of Fructose Notes | Study Chemistry for JEE - JEE C6H12O6 + C6H12O6

Sucrose D( )-glucose D(-)-Fructose

[a]D = 66.5° [a]D = 53° [a]D = -92°

Invert Sugar:

[a]D = ( 53°) - (-92°) = 39°

Surose is dextrorotatory, its specific rotation being 66.5%, D-glucose is also dextrorotatory, [a]D = 53°, but D-fructose has a large negative rotation, [a]D = -92°. Since D-fructose has a greater specific rotation than D-glucose, the resulting mixture is laevorotatory. Because of this the hydrolysis of sucrose is known as the inversion of sucrose, and the equimolecular mixture of glucose and fructose is known as invert sugar or invertose.

The document Cyclic Structure of Fructose Notes | Study Chemistry for JEE - JEE is a part of the JEE Course Chemistry for JEE.
All you need of JEE at this link: JEE

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