Question

Which of the following compounds gives a positive Tollens test?
A.

B.

C.

D.

Answer 1

Hint: Ammoniacal silver oxide is called Tollen's reagent. The Tollens test is also called the silver mirror test. Generally Tollens test or silver test is used to identify the aldehydes and alpha hydroxy ketone functional groups present in the given compounds.

Complete answer:
- In the question it is given to identify which compounds among the given options are going to respond to tollens test.
- We know that by using the Tollens test we can distinguish aldehydes from ketones.
- Aldehydes, aromatic aldehydes, and alpha hydroxy ketones are going to respond toward the tollens test and form a silver mirror at the bottom of the test tube.
- Coming to the given options, option A.

- The compound in option A does not contain any aldehyde or alpha hydroxy ketone therefore the compound in option A does not respond to tollens test.
- Coming to option B, formic acid.
- Formic acid is not a pure acid, it contains a carboxyl group as well as an aldehyde group.
- Therefore formic acid is going to respond towards tollens test.
- Coming to option C,

.

- The compound in the option is an example for alpha hydroxy ketone, therefore option C also responds to the tollens test.
- Coming to option D,

.
- The compound in the option D undergoes the following rearrangement and forms aldehyde as the product.

- Therefore the compounds in the options B, C and D are going to respond towards tollens test.

Note:
The silver ion which is present in the ammoniacal silver nitrate solution is going to be reduced to metallic silver and is going to be deposited on the glass tube bottom surface and forms a silver mirror.