Which of the following has least boiling point ?

Options

A. n-Hexane
B. n-Pentane
C. 2-Methylbutane
D. 2,2-Dimethyl propane

Answer

To determine which of the given hydrocarbons has the least boiling point, we will analyze the structures and the factors that influence boiling points.

### Step 1: Identify the Compounds
The compounds given are:
1. N-hexane (C6H14)
2. N-pentane (C5H12)
3. 2-methylbutane (C5H12)
4. 2,2-dimethylpropane (C5H12)

### Step 2: Draw the Structures
- **N-hexane**: CH3-CH2-CH2-CH2-CH2-CH3 (a straight-chain hydrocarbon with 6 carbons)
- **N-pentane**: CH3-CH2-CH2-CH2-CH3 (a straight-chain hydrocarbon with 5 carbons)
- **2-methylbutane**: CH3-CH(CH3)-CH2-CH3 (a branched hydrocarbon with 5 carbons)
- **2,2-dimethylpropane**: CH3-C(CH3)(CH3)-CH3 (a highly branched hydrocarbon with 5 carbons)

### Step 3: Analyze Boiling Points
Boiling points are influenced by intermolecular forces, which are affected by molecular size and branching:
- **N-hexane** has the highest molecular weight and a straight-chain structure, leading to stronger van der Waals forces and a higher boiling point.
- **N-pentane** has a lower molecular weight than N-hexane but is also a straight-chain hydrocarbon, resulting in a higher boiling point than branched isomers.
- **2-methylbutane** is branched, which reduces the surface area and thus the intermolecular forces compared to straight-chain hydrocarbons of the same molecular weight, leading to a lower boiling point than N-pentane.
- **2,2-dimethylpropane** is the most branched of the four, resulting in the least surface area and the weakest intermolecular forces, leading to the lowest boiling point.

### Step 4: Conclusion
Based on the analysis, **2,2-dimethylpropane** has the least boiling point among the given options.

### Final Answer
**2,2-dimethylpropane** has the least boiling point.

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