How many structural isomers are possible for `C_4H_9Br` ?

Options

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

Answer

To determine the number of structural isomers for the compound C₄H₉Br, we need to analyze the possible arrangements of carbon atoms and the placement of the bromine atom.

### Step-by-Step Solution:

1. **Identify the Molecular Formula**:
The molecular formula C₄H₉Br indicates that we have 4 carbon atoms, 9 hydrogen atoms, and 1 bromine atom.

2. **Determine the Degree of Saturation**:
The formula C₄H₉Br corresponds to a saturated compound (alkane) with the general formula CₙH₂ₙ₊₂. However, since we have a bromine atom replacing one hydrogen, we can use the formula CₙH₂ₙ₊₁Br, which is consistent with the structure of haloalkanes.

3. **Draw the Carbon Skeleton**:
The carbon skeleton can be arranged in various ways. The primary carbon chain can be straight or branched. The main chain can be:
- Butane (straight chain)
- Isobutane (branched chain)

4. **Identify Possible Isomers**:
Now, we will identify the structural isomers based on the placement of the bromine atom:
- **1-bromobutane**: Bromine is attached to the first carbon of the straight chain.
- **2-bromobutane**: Bromine is attached to the second carbon of the straight chain.
- **1-bromo-2-methylpropane**: This is the branched isomer where bromine is attached to the first carbon of isobutane.
- **2-bromo-2-methylpropane**: Bromine is attached to the second carbon of isobutane.

5. **Count the Structural Isomers**:
After analyzing the different arrangements, we find that there are a total of 4 structural isomers for C₄H₉Br:
- 1-bromobutane
- 2-bromobutane
- 1-bromo-2-methylpropane
- 2-bromo-2-methylpropane

### Conclusion:
The total number of structural isomers for C₄H₉Br is **4**.

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