Problem 58 - A Complete Resource Book in Chemistry for JEE Main

Question

When diethyl ether is treated with an excess of \(\mathrm{Cl}_{2}\) in the presence of sunlight, the product formed is (a) \(\mathrm{CH}_{3} \mathrm{CHCl}-\mathrm{O}-\mathrm{CH}_{2} \mathrm{CH}_{3}\) (b) \(\mathrm{CH}_{3} \mathrm{CHCl}-\mathrm{O}-\mathrm{CHClCH}_{3}\) (c) \(\mathrm{CCl}_{3} \mathrm{CCl}_{2}-\mathrm{O}-\mathrm{CCl}_{2} \mathrm{CCl}_{3}\) (d) \(\mathrm{CH}_{7} \mathrm{CCl}_{2}-\mathrm{O}-\mathrm{CHClCH}_{3}\)

Step-by-Step Solution

Answer

The product is (c) \(\mathrm{CCl}_3\mathrm{CCl}_2\text{-}\mathrm{O}\text{-}\mathrm{CCl}_2\mathrm{CCl}_3\).

Step 1: Understand the Reaction Type

The reaction involves diethyl ether and chlorine in the presence of sunlight. This suggests that the chlorine radicals are formed, which will substitute hydrogen atoms in the organic compound. This type of reaction is referred to as radical halogenation.

Step 2: Radical Initiation

In the presence of sunlight (UV light), chlorine molecules \((\mathrm{Cl}_2)\) dissociate into chlorine radicals \((\mathrm{Cl}\cdot)\). These radicals are highly reactive and initiate the substitution process by abstracting hydrogen atoms from diethyl ether.

Step 3: Identify the Possible Substitution Sites

Diethyl ether is structured as \(\mathrm{CH}_3\mathrm{CH}_2\text{-}\mathrm{O}\text{-}\mathrm{CH}_2\mathrm{CH}_3\). Each of the methyl \(\mathrm{CH}_3\) and methylene \(\mathrm{CH}_2\) groups can have hydrogen atoms substituted by chlorine radicals.

Step 4: Determine the Extent of Halogenation

An excess of \(\mathrm{Cl}_2\) suggests the potential for full substitution of hydrogen atoms where possible, resulting in the maximum substitution at each carbon atom. Therefore, all hydrogen atoms are replaced by chlorine atoms in a scenario with an excess of \(\mathrm{Cl}_2\).

Step 5: Assess the Product's Structure

With full substitution, each carbon atom in the ethanol components of the ether is fully chlorinated, transforming \(\mathrm{CH}_3\mathrm{CH}_2\text{-}\mathrm{O}\text{-}\mathrm{CH}_2\mathrm{CH}_3\) into \(\mathrm{CCl}_3\mathrm{CCl}_2\text{-}\mathrm{O}\text{-}\mathrm{CCl}_2\mathrm{CCl}_3\). This corresponds to option (c).

Key Concepts

Chlorination reaction

Chlorination involves the introduction of chlorine atoms into an organic molecule. This chemical reaction is especially common in radical halogenation, where chlorine acts as the halogen.

In the process of chlorination, you start with a chlorine molecule (\(\mathrm{Cl}_2\)) that splits into two chlorine radicals (\(\mathrm{Cl}\cdot\)) under UV light. These radicals are highly reactive because they have unpaired electrons.

• The chlorine radicals will aggressively replace hydrogen atoms in the organic compound.
• Radicals will continue to react until a stable molecule forms or no more reactive sites are available.

This explains why radical halogenation, specifically chlorination, often results in multiple sites being chlorinated in the presence of excess chlorine.

Organic chemistry

Organic chemistry is centered around carbon-containing compounds and involves understanding their structure, properties, and reactions. Every unique structure has its own reactivity pattern.

In organic reactions like radical halogenation, we see the interplay of electronegativity, bond strength, and molecular geometry.

• Carbon-hydrogen (C-H) bonds offer prime sites for substitution due to their relative weakness compared to C-Cl bonds.
• This reaction displays a clear example of how UV light can influence organic chemistry, providing the energy needed to form radicals that drive these reactions.

Understanding the nature of these reactions is fundamental for mastering organic chemistry concepts and predicting reaction outcomes.

Substitution reaction

Substitution reactions are a key type in both organic and inorganic chemistry, where one atom or group of atoms in a molecule is replaced by another. Radical halogenation is a perfect example of such a reaction.

In the context of radical halogenation, substitution involves chlorine radicals replacing hydrogen atoms.

• Each radical can substitute for a hydrogen atom, leading to a change in the molecular structure of the compound.
• In our example, diethyl ether undergoes complete substitution due to the excess chlorine available, resulting in the transformation of all the hydrogen atoms into chlorinated sites.

This type of reaction is vital for synthesizing new compounds, particularly in pharmaceuticals and materials science, by changing the functional groups present in a molecule.