Which of the following compounds would give a positive Tollens test? (Remember that the Tollens test involves mild basic aqueous conditions.)
(a) CH₃CH₂CH₂COCH₃
(b) CH₃CH₂CH₂CH₂CHO
(c) CH₃CH=CHCH=CHOH

Verified step by step guidance

1. Step 1: Understand the Tollens test. The Tollens test is used to identify aldehydes. It involves the use of Tollens' reagent, which contains silver ions (Ag⁺) in a basic aqueous solution. Aldehydes are oxidized to carboxylic acids, and silver ions are reduced to metallic silver, forming a silver mirror. Ketones generally do not react under these conditions.
2. Step 2: Analyze compound (a) CH3CH2CH2COCH3. This is a ketone (contains a carbonyl group bonded to two alkyl groups). Ketones do not give a positive Tollens test because they are not easily oxidized under mild basic conditions.
3. Step 3: Analyze compound (b) CH3CH2CH2CH2CHO. This is an aldehyde (contains a carbonyl group bonded to a hydrogen atom). Aldehydes are oxidized to carboxylic acids in the Tollens test, so this compound would give a positive result.
4. Step 4: Analyze compound (c) CH3CH=CHCH=CHOH. This compound contains an alcohol group (-OH) and conjugated double bonds. Alcohols do not give a positive Tollens test, and the structure does not include an aldehyde group. Therefore, this compound would not give a positive result.
5. Step 5: Summarize the findings. Compound (b) CH3CH2CH2CH2CHO is the only one that would give a positive Tollens test because it contains an aldehyde group, which reacts with Tollens' reagent under mild basic aqueous conditions.

Key Concepts

Tollens Test

The Tollens test is a qualitative test used to identify aldehydes and certain ketones. It involves the use of Tollens' reagent, which contains silver nitrate in ammonia, and reacts with aldehydes to produce a silver mirror on the test tube. This reaction occurs under mild basic conditions, making it a useful method for distinguishing between different types of carbonyl compounds.

Aldehydes vs. Ketones

Aldehydes are organic compounds characterized by the presence of a carbonyl group (C=O) at the end of a carbon chain, while ketones have the carbonyl group located within the chain. Aldehydes are generally more reactive than ketones in nucleophilic addition reactions, which is why they can be easily oxidized and detected by the Tollens test, whereas most ketones do not react under these conditions.

Mild Basic Conditions

Mild basic conditions refer to a slightly alkaline environment that facilitates certain chemical reactions without causing excessive reactivity or decomposition. In the context of the Tollens test, these conditions help stabilize the Tollens reagent and promote the oxidation of aldehydes while preventing unwanted side reactions that could interfere with the test results.