What is the possible number of stereoisomerism for 2,3- dibromobutane?

Options

A. 4
B. 3
C. 2
D. 1

Answer

To determine the possible number of stereoisomers for 2,3-dibromobutane, follow these steps:

### Step 1: Draw the Structure of 2,3-Dibromobutane
- 2,3-Dibromobutane has a four-carbon chain (butane) with bromine atoms attached to the second and third carbon atoms.
- The structure can be represented as follows:
```
Br
|
H3C - C - C - CH3
| |
Br H
```

### Step 2: Identify Chiral Carbons
- A chiral carbon is a carbon atom that has four different substituents attached to it.
- In 2,3-dibromobutane:
- The second carbon (C-2) has the following groups: bromine (Br), hydrogen (H), a methyl group (CH3), and the rest of the carbon chain (C-3).
- The third carbon (C-3) has: bromine (Br), hydrogen (H), a methyl group (CH3), and the rest of the carbon chain (C-2).

- Therefore, both C-2 and C-3 are chiral centers.

### Step 3: Count the Number of Chiral Carbons
- We have identified 2 chiral carbons (C-2 and C-3).

### Step 4: Apply the Stereoisomer Formula
- The formula for calculating the number of stereoisomers based on the number of chiral centers (n) is:
\[ \text{Number of stereoisomers} = 2^n \]
- In this case, n = 2 (the number of chiral carbons).

### Step 5: Calculate the Number of Stereoisomers
- Substitute n into the formula:
\[ \text{Number of stereoisomers} = 2^2 = 4 \]

### Step 6: Assess Symmetry
- Since the structure of 2,3-dibromobutane is symmetrical, we need to consider the possibility of meso compounds.
- A meso compound is a stereoisomer that has multiple chiral centers but is superimposable on its mirror image due to an internal plane of symmetry.

### Step 7: Final Count of Stereoisomers
- For 2,3-dibromobutane, we have 4 stereoisomers, but one of them is a meso compound.
- Therefore, the total number of unique stereoisomers is:
\[ 4 - 1 = 3 \]

### Conclusion
The possible number of stereoisomers for 2,3-dibromobutane is **3**.

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