Predict the Major and Minor Products of 2-Methyl-2-Butene with HBr in Electrophilic Addition Reaction

When 2-methyl-2-butene reacts with HBr, it undergoes an electrophilic addition reaction. Here’s a detailed look at the process and the resulting products.

The reaction begins with HBr donating a proton (H⁺) to the more substituted carbon of the double bond in 2-methyl-2-butene (the carbon with the greater number of alkyl substituents), resulting in a more stable carbocation intermediate. This leads us to the following steps:

1. Formation of the Carbocation: The double bond between the carbon atoms breaks, and the H⁺ adds to the carbon atom that is more substituted (C1 in this case). This generates a carbocation at the less substituted carbon (C2).
2. Intermediate Formation: The generated carbocation is primary, located on C2 which is now positively charged.
3. Nucleophilic Attack: Then, the bromide ion (Br^–) from HBr attacks the carbocation, forming a new bond.

There are two possible sites for the nucleophilic attack, resulting in two products:

1. Major Product: When Br^– attacks the more stable tertiary carbocation (which could occur if there’s rearrangement), the major product is 2-bromo-2-methylbutane.
2. Minor Product: The minor product, formed from the original carbocation without rearrangement, is 1-bromo-2-methylbutane.

In summary, the major product of the reaction is 2-bromo-2-methylbutane, while the minor product formed is 1-bromo-2-methylbutane, with the stability of the carbocation determining the product distribution.