The compounds which give positive Fehling's test are : (A) (B) (C) \(\mathrm{HOCH}_{2}-\mathrm{CO}-(\mathrm{CHOH})_{3}-\mathrm{CH}_{2}-\mathrm{OH}\) (D) (E) Choose the CORRECT answer from the options given below :

JEE Main · 2025 · 22 Jan 2025 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

The compounds which give positive Fehling's test are :
(A)
(B)
(C)

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

(D)
(E)

Choose the CORRECT answer from the options given below :

(A)(A),(C) and (D) Only
(B)(A),(D) and (E) Only
(C)(C), (D) and (E) Only✓ Correct
(D)(A), (B) and (C) Only

Answer: (C)

Solution

Fehling's solution oxidises free aliphatic aldehydes and

α

-hydroxy ketones (which tautomerise to expose an aldehyde), reducing

C u^{2 +}

to a brick-red

C u_{2} O

precipitate. Aromatic aldehydes and ketones lacking an adjacent

- O H

do not respond.

Benzaldehyde, an aromatic aldehyde, and acetophenone, a ketone with no

α

-hydroxy group, both fail the test.

H O C H_{2} - C O - (C H O H)_{3} - C H_{2} O H

is an

α

-hydroxy ketone (a ketose sugar) — positive.

C H_{3} C H O

is an aliphatic aldehyde — positive.

Phenylacetaldehyde,

P h C H_{2} C H O

, has its aldehyde carbon attached to a

C H_{2}

group rather than directly to the ring, so it behaves as an aliphatic aldehyde — positive.

The hydroxy-ketose, acetaldehyde and phenylacetaldehyde give a positive Fehling's test.

JEE Main · 2025 · 22 Jan 2025 · Shift 1 · Single correct option

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