Which one is most reactive towards `AgNO_3`

Options

A.
B.
C.
D.

Answer

To determine which compound is most reactive towards AgNO3, we need to analyze the stability of the carbocation intermediates formed during the reaction. The reaction involves alkyl halides, specifically bromides, reacting with silver nitrate to form silver bromide (AgBr) and a corresponding alkyl nitrate.

### Step-by-Step Solution:

1. **Identify the Compounds**:
We have several alkyl halides (bromides) to analyze for their reactivity with AgNO3.

2. **General Reaction**:
The general reaction can be represented as:
\[ RBr + AgNO_3 \rightarrow R^+ + AgBr + NO_3^- \]
Here, RBr is the alkyl bromide, which will form a carbocation (R^+) upon reaction.

3. **Formation of Carbocation**:
The stability of the carbocation formed is crucial for determining the reactivity. More stable carbocations will lead to faster reactions.

4. **Analyze Each Compound**:
- **Option A**: Contains nitrogen with two ethyl groups and a bromine. The carbocation formed here is stabilized by the +M effect from the ethyl groups and the lone pair on nitrogen.
- **Option B**: Contains oxygen (an alcohol) and bromine. The carbocation here is also stabilized by resonance due to the lone pair on oxygen. However, oxygen's high electronegativity may hinder the lone pair's participation in stabilization.
- **Option C**: Contains a benzene ring and nitrogen. The lone pair on nitrogen is involved in resonance with the benzene, reducing its availability for stabilization of the carbocation.
- **Option D**: Similar to option C, but with a primary carbocation that is not resonance stabilized, making it less reactive.

5. **Compare Stability**:
- **Options A and B**: Both can stabilize their carbocations, but the lone pair on oxygen in option B is less available due to its electronegativity.
- **Options C and D**: Both have less stable carbocations due to resonance involvement with the benzene ring, especially option D which has a primary carbocation.

6. **Conclusion**:
The most stable carbocation is formed in option A due to the effective stabilization by the ethyl groups and the nitrogen's lone pair. Thus, option A is the most reactive towards AgNO3.

### Final Answer:
**Option A** is the most reactive towards AgNO3.