Textbook Question
What alkyl halide will be obtained in greatest yield? Ignore stereoisomers.
c.
11. Radical Reactions
Anti Markovnikov Addition of Br
Problem 25b
Textbook Question
Predict the major products of the following alkene halogenation reactions. [D is the symbol for deuterium, an isotope of hydrogen.]
(b) 
Verified step by step guidance1
Identify the type of reaction: The reaction involves an alkene and DBr in the presence of H2O2, indicating a radical addition reaction.
Understand the mechanism: In the presence of peroxides (H2O2), the addition of DBr to an alkene follows an anti-Markovnikov mechanism due to the formation of radicals.
Determine the regioselectivity: In anti-Markovnikov addition, the deuterium (D) will add to the less substituted carbon of the double bond, while the bromine (Br) will add to the more substituted carbon.
Consider stereochemistry: Since the reaction proceeds via a radical mechanism, the stereochemistry of the product is not controlled, leading to a racemic mixture if chiral centers are involved.
Draw the major product: Based on the anti-Markovnikov addition, draw the structure where D is added to the terminal carbon of the alkene and Br is added to the more substituted carbon, considering the potential formation of a racemic mixture.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Alkene Halogenation
Alkene halogenation is a chemical reaction where alkenes react with halogens (like Cl2 or Br2) to form vicinal dihalides. This reaction typically occurs through an electrophilic addition mechanism, where the double bond of the alkene acts as a nucleophile, attacking the halogen molecule. Understanding the regioselectivity and stereochemistry of the products is crucial for predicting the major products.
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Halogenation Mechanism
Markovnikov's Rule
Markovnikov's Rule states that in the addition of HX (where X is a halogen) to an alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached. This principle helps predict the distribution of products in halogenation reactions, particularly when the alkene is asymmetric, leading to the formation of more stable carbocation intermediates.
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Stereochemistry of Products
Stereochemistry refers to the spatial arrangement of atoms in molecules and is crucial in determining the configuration of the products formed during alkene halogenation. The reaction can lead to the formation of different stereoisomers, including cis and trans forms, depending on how the halogen atoms add across the double bond. Recognizing the potential for stereoisomer formation is essential for accurately predicting the major products.
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