Problem 66 - A Complete Resource Book in Chemistry for JEE Main

Question

Ethyl chloride on heating with \(\mathrm{AgCN}\) forms a compounds X. The functional isomer of \(X\) will be (a) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{2}\) (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NC}\) (c) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{CN}^{2}\) (d) none of these

Step-by-Step Solution

Answer

The functional isomer of product \\(X\\) is \\(\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{CN}\\) (option b).

Step 1: Identify the Reaction Product

When ethyl chloride (C_2H_5Cl) is heated with AgCN, it forms ethyl isocyanide (C_2H_5NC). The AgCN predominantly participates in the formation of isocyanide over cyanide due to its ionic nature and availability of lone pair on nitrogen.

Step 2: Understand Functional Isomerism

Functional isomers are compounds with the same molecular formula but different functional groups. Here, the product C_2H_5NC has an isocyanide group.

Step 3: Determine the Functional Isomer

The functional isomer of ethyl isocyanide (C_2H_5NC) would have the same molecular formula but a different functional group, such as a cyanide group. Ethyl cyanide (C_2H_5CN) fits this description.

Key Concepts

Functional Isomers

Functional isomers are fascinating because they showcase how molecules with the same molecular formula can have entirely different properties. Despite having identical numbers and types of atoms, functional isomers differ in their connectivity, specifically the atoms that form the functional groups. These distinct arrangements lead to differences in chemical and physical properties. For instance, an isocyanide (R-NC) has the nitrogen and carbon bonded differently compared to a cyanide (R-CN).

• Same molecular formula but different structures.
• Different functional groups define the isomers.
• Functional isomerism is a type of structural isomerism.

When you encounter molecules like ethyl isocyanide and ethyl cyanide, you're observing functional isomerism in action. They have the same formula, yet they feature different groups (NC vs. CN), leading to unique reactivity and use cases.

Ethyl Chloride

Ethyl chloride, often symbolized as \(C_2H_5Cl\), is a vital compound in organic chemistry. It's a colorless, sweet-smelling gas used as a starting material in various reactions. Ethyl chloride belongs to the alkyl halides (haloalkanes) family, which includes compounds where a halogen atom is bonded to an alkyl group. It's crucial in synthetic procedures, especially when introducing carbon-containing groups to a molecule.

• Structure: Consists of an ethyl group bonded to a chloride ion.
• Uses: Acts as a reagent or intermediate in synthesis.
• Reactivity: Reacts with nucleophiles in substitution reactions.

When heated with \(AgCN\), ethyl chloride undergoes substitution, facilitating the production of new compounds like ethyl isocyanide.

AgCN

AgCN, or silver cyanide, is a white, odorless chemical that plays a unique role in organic reactions. As a reagent, AgCN is used in substitution reactions, where it can lead to the formation of both cyanides and isocyanides, depending on the reaction conditions.

• Properties: Ionic compound with Ag+ and CN- ions.
• Reactivity: Can lead to isocyanide formation due to its ionic nature.
• Role: Acts as a source of CN without strong cyanide reactivity.

In the reaction with ethyl chloride, AgCN prefers to form isocyanides due to the partial covalent character of the silver-cyanide bond, allowing nitrogen to be the primary point of attack.

Isocyanides

Isocyanides are intriguing organic compounds characterized by the \(NC\) group. Unlike their cyanide relatives, isocyanides have nitrogen bonded directly to carbon, imparting unique properties and reactivity to these molecules. Their peculiar structure makes them useful in various chemical applications, including pharmaceuticals and synthesis processes.

• Structure: R-NC, where R is an alkyl or aryl group.
• Formation: Commonly produced in reactions with AgCN.
• Applications: Used in organic synthesis and as building blocks in complex molecules.

The reactivity of isocyanides can be linked back to their unique nitrogen-carbon bond, which distinguishes them from other classes of compounds. Ethyl isocyanide, produced from ethyl chloride and AgCN, is a classic example, showcasing the diversity and functionality of organic chemistry.