Which of molecules A–D would you expect to give a positive permanganate test? That is, which would result in a purple KMnO₄ solution turning brown?
(c)

Verified step by step guidance

1. Step 1: Understand the permanganate test. The permanganate test is used to identify the presence of unsaturation (double or triple bonds) or certain functional groups like alcohols or aldehydes. A positive test results in the purple KMnO₄ solution turning brown due to the formation of MnO₂.
2. Step 2: Analyze the given molecule. The structure provided is an ether, specifically diisopropyl ether. It contains no double or triple bonds and no functional groups like alcohols or aldehydes that can react with KMnO₄.
3. Step 3: Recall the reactivity of ethers. Ethers are generally inert to KMnO₄ under standard conditions because they lack the functional groups required for oxidation.
4. Step 4: Compare with the criteria for a positive permanganate test. Since the molecule does not have unsaturation or oxidizable functional groups, it would not give a positive permanganate test.
5. Step 5: Conclude that the molecule shown in the image would not result in the purple KMnO₄ solution turning brown, as it does not meet the requirements for a positive test.

Key Concepts

Permanganate Test

The permanganate test is a qualitative analysis used to detect the presence of alkenes and alkynes in organic compounds. When these unsaturated hydrocarbons react with potassium permanganate (KMnO₄), the purple color of the solution is reduced to brown manganese dioxide (MnO₂), indicating a positive result. This reaction is due to the oxidation of the double or triple bonds present in the molecules.

Unsaturation in Organic Molecules

Unsaturation refers to the presence of double or triple bonds between carbon atoms in organic molecules. These unsaturated bonds are reactive and can participate in addition reactions, making them susceptible to oxidation by reagents like KMnO₄. Identifying whether a molecule is saturated (single bonds only) or unsaturated is crucial for predicting its behavior in the permanganate test.

Oxidation-Reduction Reactions

Oxidation-reduction (redox) reactions involve the transfer of electrons between substances, leading to changes in oxidation states. In the context of the permanganate test, the unsaturated organic compound is oxidized, while the permanganate ion is reduced, resulting in the color change from purple to brown. Understanding these reactions is essential for interpreting the results of the test and determining the presence of unsaturation in the tested molecules.