Which of the following has the highest point ?

Options

A. o-xylene
B. m-xylene
C. p-xylene
D. Toluene

Answer

To determine which compound has the highest melting point among ortho-xylene, meta-xylene, para-xylene, and toluene, we can follow these steps:

### Step 1: Understand the Compounds
- **Ortho-xylene**: A dimethylbenzene with two methyl groups on adjacent carbon atoms.
- **Meta-xylene**: A dimethylbenzene with two methyl groups on carbon atoms separated by one carbon.
- **Para-xylene**: A dimethylbenzene with two methyl groups on opposite carbon atoms.
- **Toluene**: A methylbenzene with one methyl group attached to a benzene ring.

### Step 2: Analyze the Structure
The melting point of organic compounds can be influenced by their molecular symmetry and packing in the solid state. Generally, more symmetrical molecules tend to have higher melting points due to better packing in the crystal lattice.

### Step 3: Compare the Symmetry
- **Ortho-xylene** has less symmetry due to the proximity of the two methyl groups.
- **Meta-xylene** has moderate symmetry but is still not as symmetrical as para-xylene.
- **Para-xylene** is the most symmetrical, with the two methyl groups positioned opposite each other, allowing for optimal packing.
- **Toluene** is less symmetrical than para-xylene but more symmetrical than ortho and meta-xylene.

### Step 4: Determine the Melting Points
- The melting points of the compounds are as follows:
- Ortho-xylene: ~-25.2 °C
- Meta-xylene: ~-47.9 °C
- Para-xylene: ~-47.9 °C
- Toluene: ~-95 °C

### Step 5: Conclusion
Based on the analysis of symmetry and the melting point values, **para-xylene** has the highest melting point due to its symmetrical structure, which allows for better packing in the crystal lattice.

### Final Answer
**Para-xylene has the highest melting point.**

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