Question

A research scholar returned to the laboratory after the lock down due to Covid-19. He kept acetone, benzaldehyde, acetaldehyde and diethyl ketone in four different bottles. The bottles contained only the label as P, Q, R and S. He forgot which bottle contained which compound. Compounds P and R only underwent iodoform test. Compound R alone gave reddish brown precipitate with Fehling's reagent. Compounds Q and R alone underwent Tollen's test. Compound S did not answer any of the above tests. Identify the compounds P, Q, R and S.

• A. P-diethyl ketone; Q-benzaldehyde; R-acetaldehyde; S-acetone
• B. P-acetone; Q-benzaldehyde; R-acetaldehyde; S-diethyl ketone
• C. P-acetone; Q-acetaldehyde; R-benzaldehyde; S-diethyl ketone
• D. P-acetaldehyde; Q-acetone; R-diethyl ketone; S-benzaldehyde
• E. P-benzaldehyde; Q-diethyl ketone; R-acetone; S-acetaldehyd

Answer 1

Answer: (E)

A research scholar had four compounds labeled as P, Q, R and S. The compounds were: acetone, benzaldehyde, acetaldehyde, and diethyl ketone.

Based on the test results: 

• P and R give the iodoform test → Indicates the presence of either CH₃CO- or CH₃CH(OH)- groups → Could be acetone or acetaldehyde
• R alone gives a reddish brown precipitate with Fehling’s reagent → This confirms R is acetaldehyde, as only aldehydes with alpha-hydrogens give this test
• Q and R give Tollen’s test → Indicates presence of aldehydes. So Q is also an aldehyde → benzaldehyde
• S does not give any test → So it must be diethyl ketone, which doesn’t respond to any of the above tests

Now match the data:

• P = Benzaldehyde
• Q = Diethyl ketone
• R = Acetaldehyde
• S = Acetone

Correct Answer:

Correct Answer: (E) P - benzaldehyde; Q - diethyl ketone; R - acetone; S - acetaldehyde