Aniline does not give coupling reactions at pH `lt 5 ` because :

Options

A. Diazonium salt converts into ` C_6 H_5 -N=N-Cl` which cannot couple
B. Aniline coverts into ` C_6 H_5 overset(o+) NH_3 Cl^(-)` , which cannot couple
C. both (1) and (2 ) .
D. Coupling only takes place in basic medium .

Answer

To solve the question of why aniline does not give coupling reactions at pH less than 5, we can follow these steps:

### Step 1: Understand the nature of aniline
Aniline is an aromatic amine with the formula C6H5NH2. It has a lone pair of electrons on the nitrogen atom, which makes it a good nucleophile.

**Hint:** Remember that nucleophiles are species that donate an electron pair to form a chemical bond.

### Step 2: Analyze the effect of pH on aniline
At pH less than 5, the environment is acidic. In acidic conditions, aniline can accept a proton (H+) from the surrounding medium, leading to the formation of anilinium ion (C6H5NH3+).

**Hint:** Consider how acids and bases interact; acids donate protons, while bases accept them.

### Step 3: Formation of anilinium ion
The reaction of aniline with protons can be represented as:
\[ \text{C6H5NH2} + \text{H}^+ \rightarrow \text{C6H5NH3}^+ \]
The resulting anilinium ion (C6H5NH3+) is positively charged and has a different electronic structure compared to neutral aniline.

**Hint:** Think about how charge affects the ability of a molecule to act as a nucleophile.

### Step 4: Nucleophilicity of anilinium ion
The anilinium ion is not a nucleophile because the positive charge on the nitrogen atom makes it less likely to donate its lone pair of electrons. As a result, it cannot participate in coupling reactions with diazonium salts.

**Hint:** Recall that nucleophiles are typically neutral or negatively charged; a positive charge can inhibit nucleophilic behavior.

### Step 5: Conclusion
Since the anilinium ion cannot act as a nucleophile, it cannot couple with diazonium salts under acidic conditions (pH < 5). Therefore, aniline does not undergo coupling reactions in such conditions.

**Final Answer:** Aniline does not give coupling reactions at pH less than 5 because it forms anilinium ion, which is not a nucleophile and cannot couple with diazonium salts.

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