Textbook Question
A halogenation intended to make compound A formed B instead.
(c) Given the two mechanisms you drew, why might B have formed selectively?
11. Radical Reactions
Free Radical Halogenation
2:28 minutesProblem 26e
Textbook Question
What are the product(s) of each of the following reactions? Disregard stereoisomers.
e. 
Verified step by step guidance1
Step 1: Identify the type of reaction. The reaction involves cyclohexane (C6H12) and chlorine (Cl2) in the presence of dichloromethane (CH2Cl2) as the solvent. This is a free radical halogenation reaction, typically initiated by light or heat.
Step 2: Understand the mechanism. Free radical halogenation proceeds via three steps: initiation, propagation, and termination. In the initiation step, chlorine molecules are split into two chlorine radicals (Cl•) by light or heat.
Step 3: Analyze the propagation step. A chlorine radical abstracts a hydrogen atom from cyclohexane, forming a cyclohexyl radical and HCl. The cyclohexyl radical then reacts with another chlorine molecule to form chlorocyclohexane and regenerate a chlorine radical.
Step 4: Consider the product. Since stereoisomers are disregarded, the major product will be chlorocyclohexane (C6H11Cl), where one hydrogen atom on the cyclohexane ring is replaced by a chlorine atom.
Step 5: Note the regioselectivity. In this case, all hydrogens in cyclohexane are equivalent, so the chlorine can attach to any carbon atom in the ring, resulting in a single product without regioselectivity concerns.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Halogenation
Electrophilic halogenation is a reaction where an alkene or alkane reacts with a halogen (like Cl2) to form a haloalkane. In this process, the halogen acts as an electrophile, attacking the electron-rich double bond or the C-H bonds in alkanes, leading to the substitution of hydrogen atoms with halogen atoms.
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Halogenation Mechanism
Mechanism of Free Radical Halogenation
The mechanism of free radical halogenation involves three main steps: initiation, propagation, and termination. In the initiation step, Cl2 is dissociated into two chlorine radicals. During propagation, these radicals react with cyclohexane to form dichlorocyclohexane and additional radicals, which can continue the reaction. Termination occurs when two radicals combine to form a stable product.
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Dichlorocyclohexane Isomers
Dichlorocyclohexane can exist in multiple isomeric forms due to the different positions where chlorine atoms can be substituted on the cyclohexane ring. However, the question specifies to disregard stereoisomers, focusing only on the structural isomers that result from the substitution of hydrogen atoms with chlorine, leading to products like 1,2-dichlorocyclohexane and 1,4-dichlorocyclohexane.
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