Which product is obtained as a major product when one mol of HBr is added to one mol of 1,3-butadiene at 193K?

Options

A. `CH_(2)Br-CH_(2)-CH=CH_(2)`
B. `CH_(3)-CHBrCH-CH_(2)`
C. `CH_(3)CH-CHCH_(2)Br`
D. `CH_(3)-CH=CBrCH_(3)`

Answer

To determine the major product obtained when one mole of HBr is added to one mole of 1,3-butadiene at 193K, we can follow these steps:

### Step 1: Draw the Structure of 1,3-Butadiene
1,3-Butadiene is a hydrocarbon with the formula C4H6. It has a linear structure with two double bonds located between the first and second carbon atoms and the third and fourth carbon atoms. The structure can be represented as follows:

```
H H H H
| | | |
H--C=C--C=C--H
| | | |
H H H H
```

### Step 2: Identify the Reaction
When HBr is added to 1,3-butadiene, it undergoes an electrophilic addition reaction. HBr will add across one of the double bonds.

### Step 3: Apply Markovnikov's Rule
According to Markovnikov's rule, when HX (in this case, HBr) adds to an alkene, the hydrogen atom (H) will attach to the carbon with the greater number of hydrogen atoms already attached, while the bromine (Br) will attach to the carbon with fewer hydrogen atoms.

In 1,3-butadiene, we have two double bonds:
1. Between C1 and C2
2. Between C3 and C4

### Step 4: Determine the Major Product
Let's analyze the addition of HBr to the two possible double bonds:

1. **If HBr adds to the C1=C2 bond:**
- H will attach to C1 (which has 2 H atoms).
- Br will attach to C2 (which has 1 H atom).
- This gives us the product: CH3-CH(Br)-CH=CH2.

2. **If HBr adds to the C3=C4 bond:**
- H will attach to C4 (which has 2 H atoms).
- Br will attach to C3 (which has 1 H atom).
- This gives us the product: CH2=CH-CH(Br)-CH3.

However, the product formed from the addition to the C1=C2 bond is more stable due to the formation of a more substituted alkene (the double bond remains between C3 and C4).

### Step 5: Write the Final Product
The major product obtained from the addition of HBr to 1,3-butadiene at 193K is:
- **CH3-CH(Br)-CH=CH2**

### Conclusion
The major product of the reaction is 3-bromo-1-butene.

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