Addition of HBr to propene

Options

A. Follows Markovnikov's rule
B. Does not follow Markovnikov's rule
C. Follows Markovnikov,'s rule but the product rearrangesto give anti-Marjovnikov's product.
D. Follows free radical mechanism.

Answer

**Step-by-Step Solution: Addition of HBr to Propene**

1. **Identify the Reactants**:
The reactant is propene, which has the structure CH₃-CH=CH₂. We are adding HBr to this alkene.

2. **Understand the Components of HBr**:
HBr consists of H⁺ (a proton) and Br⁻ (a bromide ion). When HBr is added to propene, it will dissociate into these two ions.

3. **Formation of Carbocations**:
The double bond in propene can react with the H⁺ ion. There are two possible sites for the proton to add:
- If the H⁺ adds to the terminal carbon (C1), the resulting carbocation will be CH₃-CH⁺-CH₂ (a secondary carbocation).
- If the H⁺ adds to the middle carbon (C2), the resulting carbocation will be CH₃-CH₂-CH₂⁺ (a primary carbocation).

4. **Stability of Carbocations**:
- The secondary carbocation (CH₃-CH⁺-CH₂) is more stable than the primary carbocation (CH₃-CH₂-CH₂⁺) because it is stabilized by the inductive effect of the adjacent methyl group.
- Therefore, the H⁺ will preferentially add to the terminal carbon (C1), leading to the formation of the secondary carbocation.

5. **Nucleophilic Attack by Bromide Ion**:
After the formation of the secondary carbocation, the Br⁻ ion will attack the positively charged carbon (C2) of the carbocation. This results in the addition of bromine to the carbon that had fewer hydrogen atoms.

6. **Final Product**:
The final product of this reaction is CH₃-CH(Br)-CH₂, which is 2-bromopropane. This follows Markovnikov's rule, which states that in the addition of HX to an alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms, while the halide will attach to the carbon with fewer hydrogen atoms.

7. **Conclusion**:
The addition of HBr to propene results in the formation of 2-bromopropane, following Markovnikov's rule without any rearrangement.

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