The first step of the reaction involves the breaking of the π bond and the formation of a bond between one of the two π-bonded carbons and the hydrogen on HBr. Either carbon can form this bond, so the hydrogen can be added to either carbon-1 or carbon-2.

This leaves either carbon-1 or carbon-2 as the carbocation. When the bromide ion forms a coordinate bond with the carbocation, it can either end up on carbon-1 or carbon-2 depending on where the carbocation was located.

The two carbons that form the double bond are equivalent (the molecule is symmetrical). No matter which one ends up bonded to the bromine, the resulting product is 2-bromobutane.

Both mechanisms go via a carbocation. The carbocation can end up on either carbon-1 or carbon-2.

• Carbon-1 would result in a primary carbocation.
• Carbon-2 would result in a secondary carbocation.

Secondary carbocations are more stable than primary carbocations because there are more alkyl groups attached to the positive carbon. This makes it more stable because the positive inductive effect from the alkyl groups results in a slightly lower positive charge density on the cation.

The more stable carbocation results in the major product, therefore 2-bromobutane is the major product.

In the first step, the π bond is broken and a bond is formed between the hydrogen from the catalyst and one of the two double-bonded carbons. This results in a carbocation.

There are two possible carbocations:

• The major product involves the formation of a tertiary carbocation.
• The minor product involves the formation of a secondary carbocation.

The tertiary carbocation is more stable because it has more alkyl groups attached to it (positive inductive effect), dispersing the positive charge more effectively. The more stable intermediate leads to the major product.

The two possible products are:

• 1-chloro-2-methylcyclohexane (Major Product)
• 1-chloro-3-methylcyclohexane (Minor Product)

Explanation:

The reaction proceeds via electrophilic addition. The hydrogen ion (H⁺) adds to the double bond first, creating a carbocation intermediate.

• Path A: H⁺ adds to Carbon-1, creating a positive charge on Carbon-2. This is a secondary carbocation attached to the carbon holding the methyl group.
• Path B: H⁺ adds to Carbon-2, creating a positive charge on Carbon-1. This is a secondary carbocation attached to a standard -CH₂– group.

The carbocation on Carbon-2 is more stable because the adjacent alkyl group (with the methyl substituent) exerts a stronger positive inductive effect than the standard methylene group next to Carbon-1. This extra stability drives the formation of the major product, where the chloride ion attacks Carbon-2.

Electrophilic Addition