Textbook Question
What alkyl halide will be obtained in greatest yield? Ignore stereoisomers.
e.
11. Radical Reactions
Anti Markovnikov Addition of Br
3:12 minutesProblem 14c,d
Textbook Question
What is the major product of the reaction of 2-methyl-2-butene with each of the following reagents?
c. HBr + peroxide
d. HCl + peroxide
Verified step by step guidance1
Identify the type of reaction: The reaction involves an alkene (2-methyl-2-butene) reacting with hydrogen halides (HBr and HCl) in the presence of peroxides. The presence of peroxides indicates that the reaction will proceed via a free radical mechanism, specifically the anti-Markovnikov addition of the halogen.
Understand the anti-Markovnikov rule: In the presence of peroxides, the addition of HBr to an alkene follows the anti-Markovnikov rule. This means the bromine atom will add to the less substituted carbon of the double bond, while the hydrogen atom will add to the more substituted carbon. This occurs due to the formation of a bromine radical during the reaction.
Analyze the reaction with HBr + peroxide: For 2-methyl-2-butene, the double bond is between the second and third carbons. The less substituted carbon is the terminal carbon (C1), so the bromine atom will attach to C1, and the hydrogen atom will attach to the more substituted carbon (C2). This results in the formation of the anti-Markovnikov product.
Analyze the reaction with HCl + peroxide: Unlike HBr, HCl does not undergo a free radical mechanism in the presence of peroxides. This is because the bond dissociation energy of HCl is higher than that of HBr, making it less favorable to form a chlorine radical. Therefore, the reaction will proceed via the standard Markovnikov addition mechanism, where the hydrogen atom adds to the less substituted carbon (C1), and the chlorine atom adds to the more substituted carbon (C2).
Summarize the products: For HBr + peroxide, the major product is the anti-Markovnikov addition product, where bromine is attached to the less substituted carbon. For HCl + peroxide, the major product is the Markovnikov addition product, where chlorine is attached to the more substituted carbon.
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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 (H) will attach to the carbon with the greater number of hydrogen atoms already attached, while the halide (X) will attach to the carbon with fewer hydrogen atoms. This rule helps predict the major product of electrophilic addition reactions involving alkenes.
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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 more substituted carbon, contrary to Markovnikov's Rule. This is often facilitated by the presence of peroxides, which lead to the formation of free radicals and favor the formation of the less stable radical intermediate.
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02:43Anti-Markovnikov addition of alcohols to terminal alkynes yields aldehydes
Free Radical Mechanism
The free radical mechanism involves the formation of free radicals during a chemical reaction, which are highly reactive species with unpaired electrons. In the context of alkene reactions with HBr or HCl in the presence of peroxides, this mechanism leads to the anti-Markovnikov product due to the stability of the radical intermediates formed during the reaction.
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