When 1,3 butadiene reacts with one equivalent of `Br_2` in a polar solvent the product is

Options

A.
B. `BrCH_2-CH=CH-CH_2Br`
C. `BrCH=CH-CH_2-CH_2Br`
D. none of the above

Answer

To determine the product formed when 1,3-butadiene reacts with one equivalent of Br2 in a polar solvent, we can follow these steps:

### Step 1: Understand the Structure of 1,3-butadiene
1,3-butadiene is a conjugated diene with the structure:
```
H2C=CH-CH=CH2
```
It has two double bonds, which can participate in electrophilic addition reactions.

### Step 2: Reaction with Bromine
When 1,3-butadiene reacts with bromine (Br2), the double bonds can react with bromine through an electrophilic addition mechanism. In a polar solvent, the bromine molecule becomes polarized, facilitating the reaction.

### Step 3: Formation of the Bromonium Ion
The first step involves the formation of a bromonium ion intermediate. One of the double bonds attacks a bromine atom, leading to the formation of a cyclic bromonium ion:
```
Br+
H2C-CH
| |
CH CH2
```
This intermediate has a positive charge on one of the carbons.

### Step 4: Nucleophilic Attack
The bromide ion (Br-) generated in the solution can now attack the more substituted carbon of the bromonium ion. This is due to the stability of the resulting carbocation (Markovnikov's rule).

### Step 5: Final Products
The attack can occur at either of the two positions, leading to two possible products:
1. **Product A**:
```
CH2=CH-CHBr-CH2Br
```
2. **Product B**:
```
CH2Br-CH=CH-CH2Br
```

However, due to resonance stabilization, the product with the bromine on the more substituted carbon (Product A) is favored.

### Conclusion
The major product formed when 1,3-butadiene reacts with one equivalent of Br2 in a polar solvent is:
```
CH2=CH-CHBr-CH2Br
```