How many isomers does `C_5H_11Br` have ?

Options

A. 8
B. 7
C. 6
D. 5

Answer

To determine how many isomers the compound \( C_5H_{11}Br \) has, we will follow these steps:

### Step 1: Determine the Base Structure
The molecular formula \( C_5H_{11}Br \) indicates that we have a brominated alkane. The base alkane with the formula \( C_5H_{12} \) is pentane. Therefore, we need to identify the structural isomers of pentane first.

### Step 2: Identify the Isomers of Pentane
Pentane (\( C_5H_{12} \)) has several structural isomers. The possible isomers of pentane are:
1. **n-Pentane**: A straight-chain structure (CH3-CH2-CH2-CH2-CH3).
2. **Isopentane (Methylbutane)**: A branched structure (CH3-CH(CH3)-CH2-CH3).
3. **Neopentane (Dimethylpropane)**: A more branched structure (C(CH3)4).

So, there are **3 structural isomers of pentane**.

### Step 3: Replace One Hydrogen with Bromine
Now, we will replace one hydrogen atom in each of the pentane isomers with a bromine atom to find the corresponding isomers of \( C_5H_{11}Br \).

1. **For n-Pentane**:
- Bromine can be placed on any of the terminal or internal carbons:
1. 1-bromopentane (Br on the first carbon)
2. 2-bromopentane (Br on the second carbon)
3. 3-bromopentane (Br on the third carbon)

2. **For Isopentane**:
- Bromine can be placed on:
1. 2-bromo-2-methylbutane (Br on the second carbon)
2. 3-bromo-2-methylbutane (Br on the third carbon)
3. 1-bromo-2-methylbutane (Br on the first carbon)

3. **For Neopentane**:
- Bromine can be placed on:
1. 2-bromo-2,2-dimethylpropane (Br on the central carbon)

### Step 4: Count the Isomers
Now, let's summarize the isomers:
- From n-Pentane: 3 isomers
- From Isopentane: 3 isomers
- From Neopentane: 1 isomer

### Total Isomers
Adding these together gives us:
\[ 3 + 3 + 1 = 7 \]

Thus, the total number of isomers for \( C_5H_{11}Br \) is **7**.

### Final Answer
The number of isomers for \( C_5H_{11}Br \) is **7**.

---