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Question

Which of the following is the correct evidence for cyclic glucose not having free CHO group?

A
It does not react with Schiff’s reagent
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B
It does not react with hydroxylamine
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C
Both (a) and (b)
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D
None of the above
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Solution

The correct option is C Both (a) and (b)
Despite having aldehyde group, ​glucose does not give Schiff’s test & ​it does not form the hydrogen sulphite (bisulphite) addition product with NaHSO3.​ Schiff’s reagent is a dilute solution of ​rosaniline hydrochloride whose pink ​colour has been discharged by passing SO2. Aldehyde restores pink colour​ when treated with Schiff’s reagent​ (Magenta solution in H2SO3).​ The pentaacetate of glucose does not ​react with hydroxylamine indicating​ the absence of free –CHO group. These behaviour couldn’t be​ explained by open chain structure. ​It was proposed that one of ​ –OH group may add to –CHO group ​to form a cyclic structure.​ Hence, the correct answer is option (c).

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