How many alkenes can be formed when n-butylamine is treated with nitrous acid

Explanation

To determine how many alkenes can be formed when n-butylamine is treated with nitrous acid (HNO2), we can follow these steps:

### Step 1: Understand the Reaction
When n-butylamine (C4H11NH2) reacts with nitrous acid, it undergoes a process called diazotization. The amine group (-NH2) is converted into a diazonium salt, which can then decompose to form alkenes.

### Step 2: Structure of n-Butylamine
The structure of n-butylamine is:
```
CH3-CH2-CH2-CH2-NH2
```
This means n-butylamine has a straight-chain structure with four carbon atoms.

### Step 3: Formation of the Diazonium Salt
When n-butylamine reacts with nitrous acid, it forms a diazonium salt:
```
CH3-CH2-CH2-CH2-N2^+ (leaving as N2 gas)
```

### Step 4: Carbocation Formation
Upon decomposition of the diazonium salt, a carbocation is formed. The stability of the carbocation will influence the formation of alkenes. The carbocation formed from n-butylamine is a primary carbocation, which can rearrange to form a more stable secondary carbocation.

### Step 5: Rearrangement of Carbocation
The primary carbocation can rearrange by hydride shift to form a more stable secondary carbocation:
```
CH3-CH2-CH^+-CH3 (secondary carbocation)
```

### Step 6: Alkene Formation
From the carbocation, alkenes can be formed by the loss of a proton (H+). The possible alkenes from the secondary carbocation are:
1. **But-2-ene** (CH3-CH=CH-CH3)
2. **But-1-ene** (CH2=CH-CH2-CH3)

### Step 7: Identify Different Isomers
The alkenes formed can have different configurations:
- **But-2-ene** can exist as:
- **Cis-but-2-ene** (both methyl groups on the same side)
- **Trans-but-2-ene** (methyl groups on opposite sides)

### Conclusion
Thus, the total number of different alkenes that can be formed from the reaction of n-butylamine with nitrous acid is **3**:
1. But-1-ene
2. Cis-but-2-ene
3. Trans-but-2-ene

### Final Answer
**3**