Propose mechanisms consistent with the following reactions.
(c)

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Step 1: Analyze the reaction. The starting material is an alkene, and the reagent is HBr. This indicates that the reaction involves electrophilic addition of HBr to the double bond.

Step 2: Identify the mechanism. The reaction proceeds via the formation of a carbocation intermediate. The alkene's π electrons attack the proton (H⁺) from HBr, leading to the formation of a carbocation at the more stable position.

Step 3: Consider carbocation rearrangement. The initial carbocation formed may undergo rearrangement to form a more stable carbocation, if possible. In this case, the tertiary carbocation is more stable than the secondary carbocation.

Step 4: Add the bromide ion (Br⁻). The bromide ion then attacks the carbocation, leading to the formation of the product. Since the reaction produces two products, this suggests that the bromide ion can attack either side of the carbocation, leading to regioisomeric products.

Step 5: Explain the regioselectivity. The major product is determined by Markovnikov's rule, where the bromine adds to the more substituted carbon. However, the presence of the minor product indicates that the reaction is not completely regioselective, possibly due to steric or electronic factors.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hydrohalogenation

Hydrohalogenation is an electrophilic addition reaction where alkenes react with hydrogen halides (like HBr) to form haloalkanes. The reaction involves the addition of a hydrogen atom and a halogen atom across the double bond of the alkene, resulting in the formation of two possible products due to the regioselectivity of the reaction.

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 hydrohalogenation reactions, leading to the formation of more stable carbocations during the reaction mechanism.

Carbocation Stability

Carbocation stability is a key concept in organic chemistry, as the stability of the carbocation intermediate influences the outcome of reactions. Tertiary carbocations are more stable than secondary, which are more stable than primary. The stability is due to hyperconjugation and inductive effects from surrounding alkyl groups, which can affect the pathway of the reaction and the products formed.

Propose mechanisms consistent with the following reactions.(c)