Which of the following gives positive Libermann - nitroso test?

Options

A. 2 - butanamine
B. N - ethyl -2 - pentanamine
C. N - methylpiperidine
D. N, N - dimethlycyclohexylamine

Answer

To determine which of the given compounds gives a positive Liebermann-Nitroso test, we need to understand the nature of the compounds involved and the requirements for the test.

### Step-by-Step Solution:

1. **Understanding the Liebermann-Nitroso Test**:
- The Liebermann-Nitroso test is specifically designed to identify secondary amines (2-degree amines). In this test, nitrous acid (HNO2) reacts with secondary amines to form N-nitroso amines, which can be detected.

2. **Identifying the Types of Amines**:
- We need to analyze the given options to identify which ones are secondary amines. Secondary amines have the general structure R1R2NH, where R1 and R2 are carbon-containing groups.

3. **Analyzing the Options**:
- **Option 1**: 2-butylamine
- Structure: CH3-CH2-CH(CH3)-NH2
- This is a primary amine (1-degree), so it will not give a positive test.

- **Option 2**: N-ethylpentanamine
- Structure: CH3-CH2-CH2-CH(CH2CH3)-NH2
- This is a secondary amine (2-degree), as the nitrogen is attached to two carbon-containing groups. Therefore, it will give a positive Liebermann-Nitroso test.

- **Option 3**: N-methylpiperidine
- Structure: A cyclic amine with a nitrogen atom connected to three carbon atoms.
- This is a tertiary amine (3-degree), so it will not give a positive test.

- **Option 4**: N,N-dimethylcyclohexylamine
- Structure: A nitrogen atom connected to two methyl groups and a cyclohexyl group.
- This is also a tertiary amine (3-degree), so it will not give a positive test.

4. **Conclusion**:
- The only compound that gives a positive Liebermann-Nitroso test is **Option 2: N-ethylpentanamine**.

### Final Answer:
**Option 2: N-ethylpentanamine gives a positive Liebermann-Nitroso test.**