Textbook Question
Each of the following reactions has two nucleophiles that could add to the intermediate formed by the reaction of the alkene with an electrophile. What is the major product of each reaction?
b.
10. Addition Reactions
Hydrohalogenation
2:19 minutesProblem 58a
Textbook Question
What is the major product of the reaction of 2-methyl-2-butene with each of the following reagents?
a. HBr
Verified step by step guidance1
Identify the type of reaction: The reaction of 2-methyl-2-butene with HBr is an electrophilic addition reaction, where the alkene reacts with the hydrogen halide to form an alkyl halide.
Determine the structure of 2-methyl-2-butene: The compound is a branched alkene with the double bond located between the second and third carbons. Its structure is CH₃-C(CH₃)=CH-CH₃.
Apply Markovnikov's rule: In the addition of HBr to an alkene, the hydrogen (H⁺) will add to the carbon of the double bond that has more hydrogens, and the bromine (Br⁻) will add to the carbon with fewer hydrogens. This is because the more stable carbocation intermediate is formed during the reaction.
Draw the carbocation intermediate: When H⁺ adds to the less substituted carbon of the double bond, a tertiary carbocation is formed on the more substituted carbon. This is the most stable carbocation due to hyperconjugation and inductive effects.
Add the bromide ion (Br⁻): The bromide ion will attack the positively charged carbon of the carbocation, resulting in the formation of the major product, which is a tertiary alkyl bromide.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Addition
Electrophilic addition is a fundamental reaction mechanism in organic chemistry where an electrophile reacts with a nucleophile, typically involving alkenes. In the case of 2-methyl-2-butene, the double bond acts as a nucleophile, attacking the electrophilic reagent, HBr. This process leads to the formation of a more stable carbocation intermediate, which is crucial for determining the major product.
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Markovnikov's Rule
Markovnikov's Rule states that in the addition of HX to an alkene, the hydrogen atom from HX will attach to the carbon with the greater number of hydrogen atoms already attached. This rule helps predict the regioselectivity of the reaction, guiding us to identify which carbon will bear the halide (Br in this case) in the product formed from the reaction of 2-methyl-2-butene with HBr.
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Carbocation Stability
Carbocation stability is a key concept in organic reactions, as more stable carbocations are favored during reactions. Tertiary carbocations are more stable than secondary or primary ones due to hyperconjugation and inductive effects. In the reaction of 2-methyl-2-butene with HBr, the formation of a tertiary carbocation leads to the major product, as it is the most stable intermediate formed during the reaction.
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