The number of possible organobromine compounds which can be obtained in the allylic bromination of 1 - butene with N - bromosuccinimide is

Options

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

Answer

To determine the number of possible organobromine compounds that can be obtained from the allylic bromination of 1-butene with N-bromosuccinimide (NBS), we will follow these steps:

### Step 1: Understand the Structure of 1-Butene
1-Butene has the following structure:
- CH2=CH-CH2-CH3

### Step 2: Identify the Allylic Positions
In 1-butene, the allylic positions are the carbons adjacent to the double bond. The allylic positions are:
- C2 (the carbon in the double bond)
- C3 (the carbon next to C2)

### Step 3: Generate Radicals
When N-bromosuccinimide (NBS) is used in the presence of light, it generates bromine radicals. These radicals can react at the allylic positions to form different products.

### Step 4: Possible Reactions at Allylic Positions
1. **Bromination at C2 (the carbon in the double bond)**:
- The radical can form at C2, leading to the product:
- CH2Br-CH-CH2-CH3 (1-bromo-2-butene)

2. **Bromination at C3 (the carbon next to the double bond)**:
- The radical can also form at C3, leading to the product:
- CH2=CH-CHBr-CH3 (1-bromo-3-butene)

### Step 5: Check for Stereoisomers
For each product, we need to check if stereoisomers are possible:
1. **For CH2Br-CH-CH2-CH3**:
- This compound has one chiral center at C2, which can lead to two stereoisomers (R and S configurations).

2. **For CH2=CH-CHBr-CH3**:
- This compound has a double bond and can also exhibit cis/trans isomerism. However, since it does not have a chiral center, it does not produce stereoisomers.

### Step 6: Count the Total Products
- From the first product (1-bromo-2-butene), we have 2 stereoisomers.
- From the second product (1-bromo-3-butene), we have 1 unique product (no stereoisomers).

### Conclusion
Adding these together:
- Total = 2 (from 1-bromo-2-butene) + 1 (from 1-bromo-3-butene) = 3 unique organobromine compounds.

### Final Answer
The number of possible organobromine compounds which can be obtained in the allylic bromination of 1-butene with N-bromosuccinimide is **3**.

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