Textbook Question
Provide the expected product for the reaction of each of the following alkenes with (i) HBr and (ii) HBr, H2O2
(b)
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11. Radical Reactions
Anti Markovnikov Addition of Br
3:46 minutesProblem 37b
Textbook Question
Which reagent system (HBr or HBr, H2O2) would you use to carry out the following transformations?
(b) 
Verified step by step guidance1
Identify the type of reaction: The problem involves the addition of HBr to an alkene, which can proceed via two different mechanisms depending on the presence of peroxides.
Understand the role of reagents: HBr alone will add to an alkene following Markovnikov's rule, where the hydrogen atom attaches to the less substituted carbon, and the bromine attaches to the more substituted carbon.
Consider the effect of peroxides: When HBr is used in the presence of peroxides (H₂O₂), the reaction follows an anti-Markovnikov addition. This means the bromine atom will attach to the less substituted carbon, and the hydrogen will attach to the more substituted carbon.
Analyze the desired product: Determine whether the transformation requires a Markovnikov or anti-Markovnikov addition by examining the position of the bromine in the target molecule.
Select the appropriate reagent system: Based on the desired product, choose HBr for Markovnikov addition or HBr with H₂O₂ for anti-Markovnikov addition.
Verified video answer for a similar problem:This video solution was recommended by our tutors as helpful for the problem above
Video duration:
3mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Markovnikov's Rule
Markovnikov's Rule states that in the addition of HX to an alkene, the hydrogen atom will attach to the carbon with more hydrogen atoms, while the halide (X) will attach to the carbon with fewer hydrogen atoms. This rule helps predict the major product in electrophilic addition reactions.
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Anti-Markovnikov Addition
Anti-Markovnikov addition occurs when the addition of HX to an alkene results in the halide attaching to the less substituted carbon. This is typically observed in the presence of peroxides (H₂O₂) with HBr, where the reaction proceeds via a radical mechanism, leading to the opposite regioselectivity compared to Markovnikov's Rule.
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02:43Anti-Markovnikov addition of alcohols to terminal alkynes yields aldehydes
Radical Mechanism
A radical mechanism involves the formation of free radicals, which are highly reactive species with unpaired electrons. In the presence of peroxides, HBr can initiate a radical chain reaction, leading to anti-Markovnikov addition. Understanding this mechanism is crucial for predicting the outcome of reactions involving radical initiators.
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03:28The mechanism of Radical Polymerization.
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