Which reagent system (HBr or HBr, H 2 O 2 ) would you use to carry out the following transformations? (b)

All right. Hi, everyone. So for this question, let's go ahead and choose the reagents required to carry out the following addition reaction. And so here we have an all keen on the left side and we're reacting the keen to create an a bromide at the end. No, the fact that an alkene is our starting material, right? And we're adding something in this case, bromine onto one of the carbons of the all keen indicates that this is going to be in fact an addition reaction. So the question then becomes right. What are we adding to the all keen to get the product that we're interested in? Well, let's look at our answer choices, right. Option A says HBR, option B says HBR and H2O 2. Option C says BR two and H 30 plus and option D says BR two and H2O. So here, let's go ahead and compare and contrast. HBR from BR two, first and foremost, right? Recall that when we, when we add BR two to an alkene that's going to result in a visceral di bromide where both carbons of the starting all keen will be attached to an atom of Bromy. But here, that's not quite what we want, right? Because only one carbon of the starting alkene has a bromine attached to it. So instead, right, we can add H pr because one carbon of the all keen gets a hydrogen and the other gets bromine resulting in the formation of an ocho bromide. So we know it's going to involve HBR, right. HBR is going to be our reagent for our addition reaction on the screen. But the question then becomes, is this sedition reaction Markov Kov or anti Markov Kov, let's compare right. If we look at our starting material, our double bond is in between a secondary carbon and a primary carbon. And in our product here, our bromine is attached to the primary carbon. No recall that primary carbons are less substituted than secondary carbons. So what that means is that our bromine is attaching to the less substituted carbon, which means that this is going to be anti Marconi co edition. It is antimycotic competition which means that we cannot just add HBR to our system because recall that hydro halogen nation with only HBR is a Marconi Co edition. So instead, right, our answer is going to be option B in the multiple choice because option B includes the presence of h2o which is hydrogen peroxide and recall that hydrogen peroxide is an excellent initiator for radical reactions. So because of that right, hydrogenation in the presence of peroxide yields an anti Marconi Cov product due to this radical mechanism and there you have it. So with that being said, thank you so much for watching and I hope you found this helpful.

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11. Radical Reactions

Anti Markovnikov Addition of Br

Organic Chemistry

11. Radical Reactions

Anti Markovnikov Addition of Br

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3:46 minutes

Problem 37b

Textbook Question

Which reagent system (HBr or HBr, H₂O₂) would you use to carry out the following transformations?
(b)

Verified step by step guidance

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.

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Key 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.

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.

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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