Cyclic structure of Fructose Class 12 Notes | EduRev

Chemistry for JEE

: Cyclic structure of Fructose Class 12 Notes | EduRev

The document Cyclic structure of Fructose Class 12 Notes | EduRev is a part of the Course Chemistry for JEE.

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 Class 12 Notes | EduRev

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 Class 12 Notes | EduRev

 

Hydroylsis of Sucrose:

Cyclic structure of Fructose Class 12 Notes | EduRev

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

C12H22O11 + H2O Cyclic structure of Fructose Class 12 Notes | EduRev 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.

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