NBS is a specific reagent for

Options

A. Nucleophilic substitution reaction
B. Electrophilic substitution reaction
C. Allylic substitution
D. Electrophilic addition

Answer

**Step-by-Step Solution:**

1. **Understanding NBS**: NBS stands for N-bromosuccinimide, which is a reagent used in organic chemistry. It is specifically known for its role in bromination reactions, particularly in allylic positions of alkenes.

**Hint**: Remember that NBS is a brominating agent and is often used in reactions involving free radicals.

2. **Mechanism of Action**: NBS operates through a free radical mechanism. It generates bromine radicals that can abstract hydrogen atoms from allylic positions in alkenes.

**Hint**: Focus on the concept of free radicals and how they interact with molecules to initiate reactions.

3. **Allylic Position**: The allylic position refers to the carbon atoms adjacent to a double bond. For example, in the structure CH2=CH-CH3, the CH2 group is in the allylic position relative to the double bond.

**Hint**: Identify the allylic position in any alkene structure you encounter to understand where NBS will act.

4. **Breaking of C-H Bonds**: When NBS reacts with an alkene, it abstracts a hydrogen atom from the allylic position, breaking the C-H bond. This results in the formation of a free radical at that position.

**Hint**: Visualize the breaking of bonds and the formation of radicals to grasp the reaction mechanism better.

5. **Formation of Resonance-Stabilized Radical**: The free radical formed can then resonate, leading to a more stable structure. This resonance stabilization is key to the reaction proceeding favorably.

**Hint**: Draw the resonance structures to see how the radical can stabilize itself, which is crucial for understanding the reaction's favorability.

6. **Final Product**: The final product of the reaction is a brominated compound where bromine is added at the allylic position, and HBr is released as a byproduct.

**Hint**: Always keep track of the products formed in a reaction to understand the overall transformation.

**Conclusion**: NBS is a specific reagent for allylic bromination via a free radical mechanism, leading to the formation of brominated products at the allylic position of alkenes.

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