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 can follow these steps:

### Step 1: Understand the structure of 1-butene
1-butene has the structure:
\[ \text{CH}_2=CH-CH_2-CH_3 \]

### Step 2: Identify the allylic positions
In 1-butene, the allylic positions are the carbon atoms adjacent to the double bond. In this case, the allylic positions are:
- The carbon atom at the end of the double bond (C1)
- The carbon atom next to it (C2)

### Step 3: Reaction with NBS
When 1-butene reacts with NBS, bromine can add to the allylic positions. The possible resonance structures after the reaction will lead to the formation of different brominated products.

### Step 4: Identify possible products
1. **Bromination at C1 (the terminal carbon)**:
- This leads to the formation of a compound with bromine at C1, resulting in:
\[ \text{Br-CH}_2-CH=CH-CH_3 \]

2. **Bromination at C2 (the carbon adjacent to the double bond)**:
- This leads to the formation of a compound with bromine at C2, resulting in:
\[ \text{CH}_2=CH-CH(Br)-CH_3 \]
- This compound has a chiral center at C2, which can lead to the formation of two enantiomers (R and S forms).

### Step 5: Consider geometric isomerism
For the compound with bromine at C2, we can have geometric isomers (cis and trans) due to the presence of the double bond. This gives us:
- **Cis isomer**: where the bromine and the methyl group are on the same side.
- **Trans isomer**: where the bromine and the methyl group are on opposite sides.

### Step 6: Count the unique products
From the above analysis, we can summarize the products:
1. **From bromination at C1**:
- 1 product (no stereoisomers)
2. **From bromination at C2**:
- 2 enantiomers (R and S forms) + 2 geometric isomers (cis and trans) = 4 products.

### Conclusion
Adding these together, we have:
- 1 product from C1
- 4 products from C2

Thus, the total number of possible organobromine compounds is:
\[ 1 + 4 = 5 \]

However, since the question specifies the unique organobromine compounds, we will consider the stereoisomers as unique. Therefore, the total number of unique organobromine compounds that can be formed is **4**.

### Final Answer
The number of possible organobromine compounds which can be obtained in the allylic bromination of 1-butene with N-bromosuccinimide is **4**.

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