Reaction Analysis: Electrophilic Addition to Alkenes

This reaction involves electrophilic addition of HBr to an alkene. The alkene shown is unsymmetrical, so we must apply Markovnikov's rule to predict the major product.

Step 1: Identify the Alkene Structure

The reactant is 3-methylbut-1-ene, which has the structure: $CH 2 = C H - C H (C H_{3}) - C H_{3}$

Step 2: Apply Markovnikov's Rule

Markovnikov's rule states: "In the addition of HX to an unsymmetrical alkene, the hydrogen atom adds to the carbon with the greater number of hydrogen atoms."

For 3-methylbut-1-ene, the double bond is between C1 and C2. C1 has 2 hydrogens, C2 has 1 hydrogen and is connected to a tertiary carbon (more substituted).

Step 3: Determine the Carbocation Intermediate

The proton (H⁺) adds to the less substituted carbon (C1), creating a more stable carbocation on C2:

CH 3 - C + - C H_{3} (tertiary carbocation)

Step 4: Bromide Ion Attack

The bromide ion (Br⁻) attacks the carbocation, forming the final product: 2-bromo-2-methylbutane

CH 3 - C Br - C H_{3} (with CH₃ group on the central carbon)

Final Answer

The major product is 2-bromo-2-methylbutane, which corresponds to the third option:

2-bromo-2-methylbutane

Related Topics

Markovnikov's Rule and its mechanism
Carbocation stability (primary < secondary < tertiary)
Electrophilic addition reactions
Anti-Markovnikov addition (peroxide effect)

Important Formulae and Theory

Markovnikov's Rule: In addition of HX to unsymmetrical alkenes, H adds to the carbon with more hydrogens.

Carbocation Stability Order:

3 ° > 2 ° > 1 ° > methyl

General Reaction: Alkene + HX → Alkyl halide (follows Markovnikov orientation)