Which (isomeric) amine has lowest boiling point ?

Options

A. `1^@` amine
B. `2^@` amine
C. `3^@` amine
D. cannot predict

Explanation

To determine which isomeric amine has the lowest boiling point, we need to analyze the boiling points of primary, secondary, and tertiary amines based on their structures and the presence of hydrogen bonding.

### Step-by-Step Solution:

1. **Identify the Types of Amines**:
- **Primary Amine**: This amine has one alkyl group attached to the nitrogen atom. For example, consider butylamine (CH3CH2CH2NH2).
- **Secondary Amine**: This amine has two alkyl groups attached to the nitrogen atom. An example is N-ethylbutylamine (CH3CH2NHCH3).
- **Tertiary Amine**: This amine has three alkyl groups attached to the nitrogen atom. An example is triethylamine (N(CH3)3).

2. **Draw the Structures**:
- Primary Amine: CH3CH2CH2NH2
- Secondary Amine: CH3CH2NHCH3
- Tertiary Amine: N(CH3)3

3. **Analyze Hydrogen Bonding**:
- **Primary Amine**: The primary amine can form hydrogen bonds due to the presence of two hydrogen atoms attached to the nitrogen. This leads to stronger intermolecular forces and a higher boiling point.
- **Secondary Amine**: The secondary amine can also form hydrogen bonds, but it has only one hydrogen atom available for bonding, resulting in a moderate boiling point.
- **Tertiary Amine**: The tertiary amine has no hydrogen atoms directly attached to the nitrogen atom, which means it cannot form hydrogen bonds. Therefore, it has the weakest intermolecular forces among the three types.

4. **Compare Boiling Points**:
- The boiling points of amines are influenced by the ability to form hydrogen bonds. The more hydrogen bonds that can be formed, the higher the boiling point.
- Since tertiary amines cannot form hydrogen bonds, they will have the lowest boiling point compared to primary and secondary amines.

5. **Conclusion**:
- Based on the analysis, the tertiary amine has the lowest boiling point due to the absence of hydrogen bonding.

### Final Answer:
The isomeric amine with the lowest boiling point is the **tertiary amine**.