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

Question

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

Step-by-Step Solution

Answer

The functional isomer of compound X is (a) \( \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{2} \).

Step 1: Identify Reaction Type

When ethyl chloride (C_2H_5Cl) reacts with silver cyanide (AgCN), a nucleophilic substitution occurs. However, due to the ambident nature of CN^- ion (which can attach via carbon or nitrogen), the product may vary.

Step 2: Determine the Product

Instead of the expected nitrile, the primary product formed is ethyl isocyanide (C_2H_5NC) as the reaction preferentially forms an isocyanide because silver cyanide acts as a source of the isocyanide ion.

Step 3: Identify the Functional Isomer

Functional isomers differ in functional groups, not just structure. Thus, find a compound with the formula C_3H_5N but a different functional group. Ethyl amine (C_2H_5NH_2) is a suitable functional isomer as it differs by having an amine group.

Step 4: Compare Options

Verify which given option is C_2H_5NH_2. Option (a) is ethyl amine, which corresponds to a different functional group than C_2H_5NC.

Key Concepts

Ethyl Chloride Reactions

Ethyl chloride, known chemically as \( \mathrm{C_2H_5Cl} \), is an organic compound often used in nucleophilic substitution reactions. This type of reaction involves the replacement of an atom or group of atoms in a molecule by a nucleophile. A nucleophile is an electron-rich chemical species that donates an electron pair to form a chemical bond. Think of it like a crafty scavenger that looks out for spots where it can lend its pair of electrons.
When ethyl chloride reacts with silver cyanide \( \mathrm{AgCN} \), an interesting substitution takes place. Silver cyanide can either donate its carbon or nitrogen for bond formation, as the cyanide ion is ambident, meaning it can attack through two places.
This specific reaction doesn't yield what one might typically expect, which is a nitrile. Instead, due to the affinity silver has for forming isocyanides, ethyl isocyanide \( \mathrm{C_2H_5NC} \) forms the main product. These nuances make ethyl chloride reactions intriguing and sometimes surprising!

Functional Isomers

Functional isomers are cool! They are compounds that have the same chemical formula but different functional groups. This means they differ in not just their structure, as the structural isomers do, but specifically in their functionality.
A functional group refers to a specific group of atoms within a molecule that is responsible for a characteristic of that compound. It's like the unique set of skills of a character in a game.
Here, ethyl isocyanide \( \mathrm{C_2H_5NC} \) and ethyl amine \( \mathrm{C_2H_5NH_2} \) showcase functional isomerism. While the former possesses an isocyanide group, the latter has an amine group. This means that while they may seem similar in molecular formula, their chemical behavior is very different, lending them a unique identity in organic chemistry.

• Ethyl Isocyanide - Isocyanide group \( (-\mathrm{NC}) \)
• Ethyl Amine - Amine group \( (-\mathrm{NH_2}) \)

Recognizing functional isomers is crucial because they often display very different properties and applications.

Isocyanide Formation

Isocyanides, also known as isonitriles, are fascinating compounds in organic chemistry. They have this peculiar tendency to not smell very pleasing, which is a clear indicator of their distinctive presence!
In the reaction we are looking at, the focus is on isocyanide formation. Unlike nitriles where the \( \mathrm{CN} \) group bonds carbon-to-nitrogen, in isocyanides, the bond formation occurs through nitrogen (\( \mathrm{NC} \) link).
This deviates from typical expectations and is anchored by the role \( \mathrm{AgCN} \) plays in the reaction. Silver cyanide, as part of its tricky double-edge nature, favours isocyanide linkage, emphasizing the ambidently available nitrogen's head instead of the carbon tail from the cyanide prompt.
The formation of ethyl isocyanide \( \mathrm{C_2H_5NC} \) signifies this preference. Such reactions greatly expand our scope for synthesizing diverse molecular architectures in the realm of organic chemistry.