Textbook Question
a. Propose a mechanism for the following reaction:
b. Is the initially formed carbocation primary, secondary, or tertiary?
c. Is the rearranged carbocation primary, secondary, or tertiary?
d. Why does the rearrangement occur?
10. Addition Reactions
Hydrohalogenation
2:57 minutesProblem 58b
Textbook Question
What is the major product of the reaction of 2-methyl-2-butene with each of the following reagents?
b. HI
Verified step by step guidance1
Identify the type of reaction: The reaction of 2-methyl-2-butene with HI is an electrophilic addition reaction. The double bond in the alkene acts as a nucleophile, reacting with the electrophilic hydrogen (H⁺) from HI.
Determine the regioselectivity: This reaction follows Markovnikov's rule, which states that the hydrogen atom (H⁺) will add to the carbon of the double bond that has more hydrogen atoms already attached, while the iodine (I⁻) will add to the carbon with fewer hydrogen atoms.
Protonation of the double bond: The π-electrons of the double bond attack the H⁺ from HI, forming a carbocation intermediate. The more stable carbocation will form, which in this case is the tertiary carbocation at the carbon bonded to the methyl groups.
Nucleophilic attack: The iodide ion (I⁻) acts as a nucleophile and attacks the positively charged carbocation, forming the final product.
Draw the major product: The major product will be 2-iodo-2-methylbutane, where the iodine atom is attached to the carbon that was part of the double bond and now forms a single bond with iodine.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Addition Reactions
Electrophilic addition reactions are a fundamental type of reaction in organic chemistry where an electrophile reacts with a nucleophile, typically involving alkenes. In this case, 2-methyl-2-butene, an alkene, will react with HI, where the hydrogen (H) acts as the electrophile and adds to one of the carbon atoms of the double bond, while the iodide (I) adds to the other.
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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 the greater number of hydrogen atoms already attached. This rule helps predict the major product of the reaction, as it guides the regioselectivity of the electrophilic addition, leading to the more stable carbocation intermediate.
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Carbocation Stability
Carbocation stability is crucial in determining the outcome of reactions involving alkenes. 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 HI, the formation of a more stable tertiary carbocation will favor the major product, which is influenced by the structure of the starting alkene.
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