Question

Directions: This section contains 1 paragraph. Based upon the paragraph, 3 multiple choice questions have to be answered. Each question has 4 choices (a), (b), (c) and (d), out of which ONLY ONE is correct. Passage I Alkenes undergo a variety of reactions like hydrogenation, halogenation, oxidation, epoxidation and so on. The double bond of the alkenes acts as electron donor. An unsaturated hydrocarbon gave, on treatment with alkaline \(\mathrm{KMnO}_{4}\) under hot conditions, one mole of adipic acid. The unsaturated hydrocarbon could be (a) \(\mathrm{H}_{3} \mathrm{C}-\mathrm{C} \equiv \mathrm{C}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) (b) \(\mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{2}-\mathrm{C} \equiv \mathrm{C}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\)

Short answer

Answer: (b) \(\mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{2}-\mathrm{C} \equiv \mathrm{C}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\)

Step-by-step solution

Analyze the provided unsaturated hydrocarbons

From the options provided, let's assign each hydrocarbon a letter to work with them easily: (a) X = \(\mathrm{H}_{3} \mathrm{C}-\mathrm{C} \equiv \mathrm{C}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) (b) Y = \(\mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{2}-\mathrm{C} \equiv \mathrm{C}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\)

Write down the molecular formula of adipic acid

Adipic acid has the molecular formula \(\mathrm{C}_{6} \mathrm{H}_{10} \mathrm{O}_{4}\).

Perform KMnO4 oxidation on each hydrocarbon

Oxidation through alkaline KMnO4 at hot conditions breaks both double and triple bonds in alkenes and alkynes, respectively, and adds an equal number of hydroxyl groups to the carbons involved. Now, let's perform this oxidation on each hydrocarbon: (a) X: \(\mathrm{H}_{3} \mathrm{C}-\mathrm{C}(\mathrm{OH})_{2}-\mathrm{C}(\mathrm{OH})_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) (b) Y: \(\mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{2}-\mathrm{C}(\mathrm{OH})_{2}-\mathrm{C}(\mathrm{OH})_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\)

Compare the oxidation products with adipic acid

As we compare the products of each hydrocarbon after oxidation with adipic acid, we find that only the (b) hydrocarbon, Y, yields adipic acid after oxidation. Therefore, the unsaturated hydrocarbon that yields adipic acid when treated with alkaline KMnO4 under hot conditions is: Answer: (b) \(\mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{2}-\mathrm{C} \equiv \mathrm{C}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\)

Key concepts

Hydrocarbon Oxidation

Hydrocarbon oxidation is a fundamental reaction in organic chemistry, serving as a bridge to form alcohols, ketones, acids, and other functional groups. By definition, oxidation involves the gain of oxygen and/or the loss of hydrogen within a molecule. For hydrocarbons, this often results in the transformation of available carbon-hydrogen bonds into carbon-oxygen bonds.

In practical terms, oxidation reactions are used to convert alkenes and alkynes into more oxidized organic compounds, such as acids or alcohols. Notably, these reactions require specific conditions and reagents to proceed effectively. Alkaline potassium permanganate ( KMnO_4 ) is a common oxidizing agent employed for these transformations, famed for its ability to break double and triple bonds, thus facilitating the formation of hydroxyl and carbonyl containing derivatives.

Understanding the nuances of hydrocarbon oxidation is crucial, as it underpins various synthetic pathways and is pivotal in the formation of key compounds such as adipic acid.

Alkenes and Alkynes Reactions

Alkenes and alkynes are unsaturated hydrocarbons characterized by the presence of double and triple bonds, respectively. These bonds are sites of high electron density, making them particularly reactive in chemical transformations.

The reactivity pattern of alkenes and alkynes is influenced by their ability to serve as nucleophiles, donating an electron pair to electrophilic reagents. This behavior allows them to undergo a plethora of reactions such as hydrogenation, halogenation, hydration, and various oxidation processes. Each type of reaction transforms the double or triple bond into different saturated or functionalized derivatives.

A notable reaction includes the oxidation reaction, where alkenes can be converted to diols via syn-dihydroxylation, often using reagents like KMnO_4 . This property is crucial for the conversion of certain alkenes and alkynes into specific products, such as adipic acid, through oxidative cleavage.

Adipic Acid Formation

Adipic acid ( C_6H_{10}O_4 ) is an industrially significant compound used predominantly in the production of nylon. It is synthesized through the oxidative cleavage of unsaturated hydrocarbons like alkenes and alkynes. The double or triple bonds in these hydrocarbons provide a pathway for cutting the molecular chain and adding oxygen-containing functional groups.

In a typical laboratory setting, the formation of adipic acid from hydrocarbons can be accomplished using alkaline KMnO_4 , which acts as a vigorous oxidizing agent. During this process, the hydrocarbon chain is cleaved, and di-hydroxylation occurs, resulting in an increase of oxygen content in the molecule, ultimately forming the desired adipic acid.

This transformation illustrates the functional versatility of KMnO_4 and highlights how alkene and alkyne reactions can be tuned to provide specific, valuable end products in both research and industry.

KMnO4 Oxidation Reaction

The KMnO_4 oxidation reaction is a powerful method used for the oxidative transformation of organic compounds. Potassium permanganate ( KMnO_4 ) is a potent oxidizing agent that facilitates the introduction of oxygen into substrates, particularly hydrocarbons.

This reagent is commonly employed in the oxidation of unsaturated hydrocarbons, including alkenes and alkynes. Under alkaline conditions, KMnO_4 induces cleavage of the carbon-carbon double or triple bonds, converting them into hydroxylated products. For instance, it is capable of transforming terminal alkynes into carboxylic acids, which is integral for the synthesis of compounds like adipic acid.

Experimentally, the use of KMnO_4 necessitates careful control of conditions, such as temperature and pH, to ensure complete reaction and desired product formation. The versatility and robustness of KMnO_4 as an oxidant make it a staple in organic synthesis, especially for designing pathways to convert basic alkenes and alkynes into more complex and functionally enriched molecules.