Chlorination of alkane is an example of:

Question

Examoogle · Accepted Answer

The correct answer is Option D: substitution reaction. The chlorination of an alkane is a classic example of a free-radical substitution reaction. In this process, a hydrogen atom in the alkane molecule is replaced by a chlorine atom in the presence of sunlight (ultraviolet light) or heat.

Step-by-Step Solution & Concepts:
The chlorination of an alkane is a classic example of a free-radical substitution reaction. In this process, a hydrogen atom in the alkane molecule is replaced by a chlorine atom in the presence of sunlight (ultraviolet light) or heat.

Working Principle: The mechanism occurs in three steps: initiation, propagation, and termination. In the initiation step, ultraviolet light causes the homolytic fission of the chlorine molecule ($Cl_2$) into two chlorine free radicals ($Cl^\bullet$). These radicals then attack the alkane molecule, abstracting a hydrogen atom to form a hydrogen chloride ($HCl$) molecule and an alkyl radical, which subsequently reacts with another $Cl_2$ molecule to produce the chloroalkane product.

Key Formulas: $CH_4 + Cl_2 \xrightarrow{h
u} CH_3Cl + HCl$ — General chlorination of methane; $Cl_2 \xrightarrow{h
u} 2Cl^\bullet$ — Homolytic fission initiation step

Key Points: It is a free-radical substitution reaction.; Requires UV light ($h
u$) or high temperature to initiate.; The reaction proceeds through a chain mechanism.; Multiple substitutions can occur, leading to products like $CH_2Cl_2$, $CHCl_3$, and $CCl_4$.

Advantages: Important in industrial production of chlorinated solvents.

Disadvantages: Poor selectivity in alkanes higher than ethane (mixture of isomers).; Difficult to control the degree of substitution.

Applications: Production of alkyl halides.; Intermediate steps in the synthesis of pharmaceuticals and polymers.

Additional Info: The reaction is exothermic.. Option A (Addition reaction) is wrong because alkanes lack pi bonds necessary for addition. Option B (Rearrangement) is wrong as no structural skeleton change occurs. Option C is wrong because it describes a combination of reaction types not defined as the primary mechanism for this specific process.

Answer: D is correct — Chlorination of an alkane is a free-radical substitution reaction where a hydrogen atom is replaced by a chlorine atom.

Exam Tip: Always remember: Alkanes undergo substitution, while Alkenes/Alkynes undergo addition due to the presence of multiple bonds.

Examoogle · Answer

Option A: addition reaction

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Option B: rearrangement reaction

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Option C: both addition and substitution chain reaction

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