Solving Anti-Markovnikov Addition Rxns with Peroxide

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In summary, the conversation is about solving organic chemistry reactions using a new textbook with a confusing answer key. The reactions involve anti-markovnikov addition of HBr to an alkene using a peroxide. The speaker believes that these reactions would generate a maximum of four different products and is seeking confirmation about the stereochemistry. The reactions and predicted products are discussed, with some confusion about the number of products in the second reaction. The book may not provide a clear description of the stereochemistry for the products.
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Spirochete
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I'm trying to solve some organic chem reactions out of a new textbook with an answer key that's confusing me. All three rxns involve anti-markovnikov addition of HBr to an alkene using a peroxide. A peroxide radical generates a bromine radical, the electrophile which then adds to the least subsituted carbon. I would think that these rxns would be non-sterospecific, thus generating a maximum of four different products. Here are the reactions and what I think the answers should be.

I don't care about exact answers I'm just want to confirm stereochemistry:

1) 2-methylpropene +HBr + peroxide--->a racemic mix of two products, right?

2) 1-methylcyclopropene+HBr+peroxide---> 2 different racemic mixtures, four total different products

3) 1-phenylpropene + HBr +peroxide---->again, a racemic mixture of two product


My book is ambiguous in it's description of stereochem for the products, perhaps because it's an advanced text which just assumes this stuff is obvious.
 
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edit: OOPS! My bad...
I don't get 4 products for 2). Do you postulate that the double bond migrates?
 
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I can confirm that your understanding of the anti-Markovnikov addition reactions with peroxide is correct. The peroxide radical does indeed generate a bromine radical, which then adds to the least substituted carbon of the alkene. This results in a non-stereospecific reaction, meaning that it can produce a maximum of four different products.

For the first reaction, 2-methylpropene + HBr + peroxide, you are correct in saying that it will result in a racemic mixture of two products. This means that both enantiomers (mirror images) of the product will be formed in equal amounts.

For the second reaction, 1-methylcyclopropene + HBr + peroxide, there will be two different racemic mixtures formed, resulting in a total of four different products. This is because the cyclopropene ring adds an additional level of complexity, leading to two possible orientations for the addition of the bromine radical.

Similarly, for the third reaction, 1-phenylpropene + HBr + peroxide, a racemic mixture of two products will be formed.

It is common for advanced textbooks to assume that certain concepts are understood, so it is always a good idea to confirm your understanding and ask for clarification if needed. Overall, your understanding of the stereochemistry involved in these reactions is accurate.
 

1. What is the purpose of using peroxide in anti-Markovnikov addition reactions?

The use of peroxide in anti-Markovnikov addition reactions is to initiate a free radical mechanism that leads to the formation of the anti-Markovnikov product. This product is formed by adding the hydrogen atom to the less substituted carbon, contrary to the Markovnikov rule which states that the hydrogen atom is added to the more substituted carbon.

2. How does peroxide initiate the free radical mechanism in anti-Markovnikov addition reactions?

Peroxide acts as a radical initiator by breaking the O-O bond and forming two free radicals. These radicals then attack the alkene, creating a new radical that can add to the alkene in an anti-Markovnikov manner.

3. What are the advantages of using peroxide in anti-Markovnikov addition reactions?

Using peroxide in anti-Markovnikov addition reactions allows for the formation of products that are not easily accessible through other methods. It also provides a way to control regioselectivity in reactions that would normally follow the Markovnikov rule.

4. Can any kind of peroxide be used in anti-Markovnikov addition reactions?

No, only certain types of peroxides are suitable for use in anti-Markovnikov addition reactions. These include hydrogen peroxide, tert-butyl hydroperoxide, and di-tert-butyl peroxide. Other peroxides may not be stable enough to initiate the required free radical mechanism.

5. Are there any limitations to using peroxide in anti-Markovnikov addition reactions?

One limitation is that the reaction must be conducted under specific conditions, such as in the presence of light or at high temperatures, to ensure that the peroxide is efficiently activated. Additionally, peroxide can also lead to over-oxidation if not used carefully, resulting in the formation of unwanted by-products.

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