Major Product Formation in Alkene Addition Reaction

This question involves determining the major product when an alkene undergoes hydrohalogenation (addition of HBr). The given reactant is 3-methylbut-1-ene, which has the structure:

3-methylbut-1-ene

Step 1: Identify the Reaction Type

This is an electrophilic addition reaction where HBr adds across the double bond following Markovnikov's rule.

Step 2: Apply Markovnikov's Rule

Markovnikov's rule states: "The hydrogen atom adds to the carbon with the greater number of hydrogen atoms."

For 3-methylbut-1-ene (CH ${CH}_{2}$ =C(CH ${CH}_{3}$ )CH ${CH}_{3}$ ):

Carbon 1 (terminal carbon) has 2 hydrogens
Carbon 2 has no hydrogens (substituted with methyl group)

Hydrogen adds to carbon 1, bromine adds to carbon 2.

Step 3: Determine the Carbocation Stability

The reaction proceeds through a carbocation intermediate. The more stable carbocation forms faster:

Primary carbocation: less stable

Secondary carbocation: more stable

Tertiary carbocation: most stable

In this case, adding H⁺ to carbon 1 creates a tertiary carbocation at carbon 2, which is highly stable.

Step 4: Identify the Major Product

The major product is 2-bromo-2-methylbutane:

2-bromo-2-methylbutane

Final Answer

The major product is the fourth option: 2-bromo-2-methylbutane

Related Topics

Electrophilic Addition Reactions
Markovnikov's Rule
Carbocation Stability
Alkene Reactivity
Regioselectivity in Organic Reactions

Important Formulae and Theory

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

Carbocation Stability Order:

Tertiary > Secondary > Primary > Methyl

General Reaction:

R-CH=CH ${CH}_{2}$ + HBr → R-CHBr-CH ${CH}_{3}$

Mechanism: Electrophilic addition via carbocation intermediate