The reaction involves an alkene undergoing electrophilic addition with HBr. The alkene is unsymmetrical, so we must consider Markovnikov's rule, which states that the hydrogen atom adds to the carbon with the greater number of hydrogen atoms, and the halogen adds to the carbon with fewer hydrogen atoms. However, the presence of a peroxide (ROOR) changes the mechanism to anti-Markovnikov addition via a free radical process.

Step 1: Identify the Reagents
The reagent is HBr in the presence of peroxide (ROOR). Peroxides initiate a free radical addition, leading to anti-Markovnikov addition.

Step 2: Analyze the Alkene
The alkene is 1-methylcyclohexene. The double bond is between C1 and C2, where C1 is part of the ring and has one hydrogen, and C2 is the methyl-substituted carbon (tertiary carbon).

Step 3: Mechanism of Anti-Markovnikov Addition
In the presence of peroxide, HBr adds via a free radical mechanism. The bromine radical (Br•) adds first to the less substituted carbon of the double bond (following anti-Markovnikov rule), and then hydrogen adds to the more substituted carbon.

For 1-methylcyclohexene:
- The less substituted carbon is C1 (secondary carbon).
- The more substituted carbon is C2 (tertiary carbon).

So, Br• adds to C1, and H adds to C2. The major product is 1-bromo-1-methylcyclohexane.

Final Answer: The major product is $1 - bromo - 1 - methylcyclohexane$ , which corresponds to the structure with Br attached to the tertiary carbon (the carbon originally part of the double bond with the methyl group).

Related Topics

Electrophilic Addition: Alkenes undergo addition reactions with electrophiles like HX. Normally, Markovnikov's rule is followed, but peroxides alter the mechanism to free radical addition, resulting in anti-Markovnikov products.

Free Radical Addition: Initiated by peroxides, this mechanism involves radicals adding to the double bond. The stability of the intermediate carbon radical dictates the regiochemistry, with the radical preferring the more substituted carbon.

Formulae

Markovnikov's Rule: H adds to the carbon with more H atoms.
Anti-Markovnikov Addition (with peroxide): Br adds to the less substituted carbon.