Question

An organic compound of molecular formula \[{C_3}{H_6}O\] did not give a silver mirror with Tollens’ reagent but gave an oxime with hydroxylamine. It may be:
A. $C{H_2} = CH - C{H_2} - OH$
B. $C{H_3}COC{H_3}$
C. $C{H_3}C{H_2}CHO$
D. $C{H_2} = CH - OC{H_3}$

Answer 1

Hint: Tollens reagent is a mixture of silver nitrate and ammonia solution. It is used to determine the presence of aldehydes or ketones in a carbonyl functional group.

Complete step by step answer: The presence of a carbonyl functional group is determined by DNP (2,4-dinitrophenyl hydrazine) test. The reagent used is also known as Brady’s reagent. It reacts with carbonyl compounds to yield an orange precipitate. If a compound is found to contain a carbonyl functional group, the next step is to identify whether the compound is an aldehyde or a ketone.
For this the carbonyl compound is treated with Tollens’ reagent. Tollens reagent is a composition of silver nitrate, ammonia and sodium hydroxide. Out of aldehyde and ketone only aldehyde gives a silver mirror with Tollens’ reagent. The reaction is an oxidation reduction reaction where an aldehyde is oxidized to acid and the silver (I) is reduced to silver (0). Ketones do not undergo any reaction with Tollens’ reagent.
Carbonyl compounds react with hydroxylamine to produce oxime. This is a type of condensation reaction where aldehydes react to generate aldoximes and ketones react to generate ketoximes.
The given organic compound gives oxime with hydroxylamine, so the compound contains a carbonyl functional group.
Thus option A and D are incorrect i.e. \[C{H_2} = CH - C{H_2} - OH\] and $C{H_2} = CH - OC{H_3}$ do not match with the given compound.
The given compound did not give silver mirror with Tollens’ reagent, so it is definitely a ketone and not an aldehyde.
Thus option B is correct and option C is incorrect i.e. the aldehyde $C{H_3}C{H_2}CHO$ is not the given compound.
Hence the compound with molecular formula \[{C_3}{H_6}O\] is $C{H_3}COC{H_3}$.

Note: The DNP test is a preliminary test to check the presence of a carbonyl functional group. The presence of hydrogen atom attached to aldehyde makes it easily oxidized than the ketone. Like Tollens’ test, the presence of aldehyde can also be confirmed using Fehling’s test. In this test Fehling’s solution oxidizes the aldehyde and not the ketone.