KCET · Chemistry · Biomolecules

Sucrose is dextrorotatory but after hydrolysis the mixture show laevorotation, this is because of

A laevorotation of glucose is more than dextrorotation of fructose.
B sucrose is a non-reducing sugar.
C racemic mixture is formed.
D laevorotation of fructose is more than dextrorotation of glucose.

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Answer & Solution

Correct Answer

(D) laevorotation of fructose is more than dextrorotation of glucose.

Step-by-step Solution

Detailed explanation

Sucrose exhibits laevorotation upon
hydrolysis due to the specific arrangement of its constituent molecules. When sucrose is hydrolysed, it undergoes a chemical reaction that breaks the glycosidic bond, resulting in the formation of glucose and fructose as individual monosaccharides.
Since the rotation of glucose is opposite in sign to that of fructose, their combined effect leads to the observed laevorotation i.e. (laevorotation of fructose is more than dextrorotation of glucose.)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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