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 conditions under which this test is positive. The Liebermann-Nitroso test is positive for phenols and secondary amines.

### Step-by-Step Solution:

1. **Identify the Compounds**: The question provides several amines. We need to identify whether each compound is a primary, secondary, or tertiary amine, as only secondary amines will give a positive Liebermann-Nitroso test.

2. **Analyze Each Compound**:
- **2-butanamine**: This is a primary amine (structure: CH3-CH2-CH(NH2)-CH3). Primary amines do not give a positive Liebermann-Nitroso test.
- **N-ethyl-2-pentanamine**: This is a secondary amine (structure: CH3-CH2-CH(NH)-CH2-CH3). Secondary amines do give a positive Liebermann-Nitroso test.
- **N-methylpyridine**: This is a tertiary amine (structure: a nitrogen atom bonded to three carbon atoms). Tertiary amines do not give a positive Liebermann-Nitroso test.
- **N,N-dimethylcyclohexylamine**: This is also a tertiary amine (structure: cyclohexyl ring with a nitrogen atom bonded to two methyl groups). Tertiary amines do not give a positive Liebermann-Nitroso test.

3. **Conclusion**: Among the compounds analyzed, only **N-ethyl-2-pentanamine** is a secondary amine and will give a positive Liebermann-Nitroso test.

### Final Answer:
The compound that gives a positive Liebermann-Nitroso test is **N-ethyl-2-pentanamine**.

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