Which of the following will be the major product when 3 - phenylpropene reacts with HBr?

Options

A. `C_(6)H_(5)CH_(2)CHBrCH_(3)`
B. `C_(6)H_(5)CHBrCHCH_(2)`
C. `C_(6)H_(5)CH_(2)CH_(2)CH_(2)Br`
D. `C_(6)H_(5)CHBrCH_(2)CH_(3)`

Answer

To determine the major product when 3-phenylpropene reacts with HBr, we can follow these steps:

### Step 1: Identify the structure of 3-phenylpropene
3-phenylpropene has a phenyl group (C6H5) attached to the third carbon of a propene chain. The structure can be represented as:
```
C6H5
|
H2C=C-CH2-CH3
```

### Step 2: Understand the reaction with HBr
When 3-phenylpropene reacts with HBr, the reaction involves the addition of HBr across the double bond. HBr dissociates into H⁺ and Br⁻ ions.

### Step 3: Mark the double bond
The double bond is between the first and second carbon of the propene chain. We can denote the carbons as follows:
```
1 2 3
H2C = C - CH2 - CH3
```

### Step 4: Protonation of the double bond
The double bond can react with H⁺ from HBr. The proton (H⁺) can add to either carbon of the double bond. If H⁺ adds to carbon 1, we will have a carbocation at carbon 2. If H⁺ adds to carbon 2, we will have a carbocation at carbon 1.

### Step 5: Determine the more stable carbocation
- If H⁺ adds to carbon 1, we get a secondary carbocation at carbon 2.
- If H⁺ adds to carbon 2, we get a primary carbocation at carbon 1.

The secondary carbocation is more stable due to the resonance stabilization provided by the adjacent phenyl group.

### Step 6: Rearrangement of the carbocation
The secondary carbocation can undergo rearrangement. The positive charge can shift to carbon 3, allowing the phenyl group to stabilize the charge through resonance. This results in a more stable carbocation.

### Step 7: Nucleophilic attack by Br⁻
Once the more stable carbocation is formed, the Br⁻ ion will attack the carbocation, leading to the final product.

### Step 8: Write the final product
The final product after the attack of Br⁻ on the more stable carbocation will be:
```
C6H5-CHBr-CH2-CH3
```
This can also be represented as:
```
C6H5-CH-CH2-CH3
|
Br
```

### Conclusion
The major product when 3-phenylpropene reacts with HBr is 1-bromo-3-phenylpropane.