Which of the following can be used to prepare 3-bromo propene ?

Options

A. `CH_(3)CH =CH_(2) +Br_(2) overset( C CI_(4)) underset(30^(@)C)(to)`
B. `CH_(3)CH=CH_(2)+ N - " bromo succinimide " to `
C. `CH_(2) =CH -CH_(3) +PBr_(3) to`
D. CH_(2) =CH -CH_(3) overset(HBr)(to)`

Answer

To prepare 3-bromo propene, we need to consider the structure of the compound and the reagents that can facilitate the bromination at the correct position. Here’s a step-by-step solution:

### Step 1: Understand the Structure of 3-Bromo Propene
3-Bromo propene has the following structure:
- The propene backbone consists of three carbon atoms.
- The bromine atom is attached to the third carbon (C-3) of the propene chain.

### Step 2: Identify the Suitable Reagents
To introduce a bromine atom at the C-3 position, we need to use a reagent that can selectively brominate the allylic position.

### Step 3: Consider N-Bromosuccinimide (NBS)
N-Bromosuccinimide (NBS) is a reagent that is commonly used for allylic bromination. It selectively brominates the allylic position due to the stability of the allylic radical formed during the reaction.

### Step 4: Reaction Mechanism with NBS
1. **Formation of the Allylic Radical**: When NBS is used in the presence of a double bond, it generates bromine radicals that can abstract a hydrogen atom from the allylic position (C-2 or C-3).
2. **Bromination**: The bromine radical then adds to the carbon atom that is adjacent to the double bond, leading to the formation of 3-bromo propene.

### Step 5: Conclusion
Thus, the correct reagent to prepare 3-bromo propene is N-bromosuccinimide (NBS), as it effectively brominates the allylic carbon.

### Final Answer
The reagent that can be used to prepare 3-bromo propene is **N-bromosuccinimide (NBS)**.

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