Highest boiling point is expected for

Options

A. 2,2-dimethyl butane
B. 3-methyl pentane
C. 2-methyl pentane
D. n-heptane

Answer

To determine which compound has the highest boiling point among the given options, we need to consider the structure of each compound and how it affects the boiling point. The boiling point of hydrocarbons is influenced by the strength of intermolecular forces, particularly Van der Waals forces, which increase with the number of carbon atoms and the surface area of the molecule.

### Step-by-Step Solution:

1. **Identify the Compounds**:
The compounds given are:
- 2,2-dimethylbutane
- 3-methylpentane
- 2-methylpentane
- n-heptane

2. **Analyze the Structure**:
- **2,2-dimethylbutane**: This compound has a branched structure with a total of 5 carbon atoms. The branching reduces the surface area, leading to weaker Van der Waals forces.
- **3-methylpentane**: This compound has a straight chain with one methyl branch, totaling 6 carbon atoms. The presence of one branch slightly reduces the boiling point compared to a straight chain.
- **2-methylpentane**: Similar to 3-methylpentane, it has a straight chain with one methyl branch, also totaling 6 carbon atoms. The effect on boiling point is similar to that of 3-methylpentane.
- **n-heptane**: This compound has a straight-chain structure with 7 carbon atoms. The straight-chain structure maximizes surface area and thus has stronger Van der Waals forces.

3. **Compare the Number of Carbon Atoms**:
The boiling point generally increases with an increase in the number of carbon atoms due to increased Van der Waals forces. Here, n-heptane has the most carbon atoms (7), while the others have fewer (5 or 6).

4. **Consider the Effects of Branching**:
Branching in hydrocarbons decreases the boiling point due to a reduction in surface area. Both 2,2-dimethylbutane and the methyl-substituted pentanes have branching, which will lower their boiling points compared to n-heptane.

5. **Conclusion**:
Since n-heptane has the highest number of carbon atoms (7) and is a straight-chain alkane, it will have the highest boiling point among the given options.

### Final Answer:
The compound with the highest boiling point is **n-heptane**.

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