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Question 57

The compounds which give positive Fehling's test are :

(A). 

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(B). 

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(C). $$ HOCH_{2} - CO - (CHOH)_{3}-CH_{2}-OH $$

(D). $$CH_{3}-CHO$$

(E). 

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Choose the correct answer from the options given below :

A) Benzaldehyde: Gives a negative result. Although it is an aldehyde, aromatic aldehydes are generally not oxidized by the relatively weak Fehling's solution.

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B) Acetophenone: Gives a negative result. It is a ketone, and ketones lack the oxidizable hydrogen atom attached to the carbonyl carbon necessary to reduce Fehling's solution.

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C) Fructose: Gives a positive result. Despite being a keto-hexose, it undergoes tautomerization under the alkaline conditions of the test to form oxidizable aldoses.
$$ HOCH_{2} - CO - (CHOH)_{3}-CH_{2}-OH $$

D) Acetaldehyde: Gives a positive result. As an aliphatic aldehyde, it is easily oxidized by the $$Cu^{2+}$$ ions in Fehling's solution to form a carboxylic acid and a red precipitate of $$Cu_2O$$.

E) Phenylacetaldehyde: Gives a positive result. Even though it contains an aromatic ring, the aldehyde group is attached to an aliphatic side chain, allowing it to behave like a typical aliphatic aldehyde in this test.

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