In presence of peroxides , the addition of HBr to propene occurs according to ______ rule and gives _____ as the major product but in absence of peroxides, addition occurs according ______ rule and gives _______ as the major product.

Answer

To solve the question regarding the addition of HBr to propene in the presence and absence of peroxides, we will follow these steps:

### Step-by-Step Solution:

1. **Identify the Reaction Context**:
- The question asks about the addition of HBr to propene (C3H6) and how the presence or absence of peroxides affects the product formed.

2. **Understand the Role of Peroxides**:
- In the presence of peroxides, the addition of HBr to alkenes follows a different mechanism compared to when peroxides are absent. This is known as the peroxide effect or Kharasch effect.

3. **Addition in Presence of Peroxides**:
- When HBr is added to propene in the presence of peroxides, the reaction follows **Anti-Markovnikov's rule**. This means that the bromine atom (Br) will add to the less substituted carbon atom of the double bond.
- The major product formed in this case is **1-bromopropane** (CH3CH2CH2Br).

4. **Addition in Absence of Peroxides**:
- When HBr is added to propene in the absence of peroxides, the reaction follows **Markovnikov's rule**. According to this rule, the bromine atom (Br) will add to the more substituted carbon atom of the double bond.
- The major product formed in this case is **2-bromopropane** (CH3CHBrCH3).

### Final Answer:
- In presence of peroxides, the addition of HBr to propene occurs according to **Anti-Markovnikov's rule** and gives **1-bromopropane** as the major product.
- In absence of peroxides, addition occurs according to **Markovnikov's rule** and gives **2-bromopropane** as the major product.