How many chiral stereoisomers can be drawn for 2 - bromo - 3 - chlorobutane ?

Options

A. 2
B. 3
C. 4
D. 5

Answer

To determine how many chiral stereoisomers can be drawn for 2-bromo-3-chlorobutane, follow these steps:

### Step 1: Identify the Structure
First, we need to draw the structure of 2-bromo-3-chlorobutane. The molecular formula is C4H8BrCl. The structure can be represented as follows:

```
CH3
|
CH3-CH-CH-CH2
| |
Br Cl
```

### Step 2: Identify Chiral Centers
Next, we identify the chiral centers in the molecule. A chiral center is typically a carbon atom that is bonded to four different groups. In 2-bromo-3-chlorobutane, we can see that:

- The carbon at position 2 (attached to Br, CH3, H, and the rest of the chain) is a chiral center.
- The carbon at position 3 (attached to Cl, CH2, H, and the rest of the chain) is also a chiral center.

Thus, we have **two chiral centers**.

### Step 3: Calculate the Number of Stereoisomers
The number of chiral stereoisomers can be calculated using the formula:
\[ \text{Number of stereoisomers} = 2^n \]
where \( n \) is the number of chiral centers.

In this case, since we have 2 chiral centers:
\[ n = 2 \]
\[ \text{Number of stereoisomers} = 2^2 = 4 \]

### Step 4: Conclusion
Therefore, the total number of chiral stereoisomers for 2-bromo-3-chlorobutane is **4**.