The number of structural and configurational isomers of a bromo compound, `C_(5)H_(9)Br`, formed by the additionn of HBr to 2-penthyne respectively are

Options

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

Explanation

To solve the problem regarding the number of structural and configurational isomers of the bromo compound \( C_5H_9Br \) formed by the addition of HBr to 2-pentyne, we will follow these steps:

### Step 1: Identify the Structure of 2-Pentyne
2-Pentyne has the formula \( C_5H_{10} \) and its structure can be represented as:
\[ CH_3C \equiv CCH_2CH_3 \]

### Step 2: Understand the Reaction with HBr
When HBr is added to 2-pentyne, it follows Markovnikov's rule, which states that the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms.

### Step 3: Determine Possible Products
1. **First Product**: If H+ attacks the first carbon (C1), the bromine (Br-) will attach to the second carbon (C2):
\[ CH_3C(Br)=C(CH_2CH_3)H \]
This product can be represented as:
\[ CH_3CBr=CH(CH_2CH_3) \]

2. **Second Product**: If H+ attacks the second carbon (C2), then Br- will attach to the first carbon (C1):
\[ CH_3C=CH(Br)CH_2CH_3 \]
This product can be represented as:
\[ CH_3C=CHBrCH_2CH_3 \]

### Step 4: Count the Structural Isomers
From the above reactions, we have identified two structural isomers:
1. \( CH_3CBr=CH(CH_2CH_3) \)
2. \( CH_3C=CHBrCH_2CH_3 \)

### Step 5: Identify Configurational Isomers
Configurational isomers arise from the different spatial arrangements of atoms or groups around a double bond. Each structural isomer can have geometric (cis/trans or E/Z) isomers.

1. **For the first structural isomer** \( CH_3CBr=CH(CH_2CH_3) \):
- **Cis isomer**: Both Br and CH3 on the same side.
- **Trans isomer**: Br and CH3 on opposite sides.

2. **For the second structural isomer** \( CH_3C=CHBrCH_2CH_3 \):
- **Cis isomer**: Both Br and CH3 on the same side.
- **Trans isomer**: Br and CH3 on opposite sides.

### Step 6: Count the Configurational Isomers
Each of the two structural isomers has two configurational isomers (cis and trans), giving us a total of:
- 2 (from the first isomer) + 2 (from the second isomer) = 4 configurational isomers.

### Final Count
- **Structural Isomers**: 2
- **Configurational Isomers**: 4

### Conclusion
The number of structural isomers is 2, and the number of configurational isomers is 4.