There are two compounds A and B of molecular formula `C_(9)H_(18)O_(3)`. A has higher boiling point than B. What are the possible structures of A and B?

Options

A.
B.
C.
D.

Answer

To determine the possible structures of compounds A and B with the molecular formula \( C_9H_{18}O_3 \), where A has a higher boiling point than B, we need to consider the factors that influence boiling points, particularly the type of intermolecular forces present in each compound.

### Step-by-Step Solution:

1. **Understanding the Molecular Formula**:
- Both compounds A and B have the same molecular formula \( C_9H_{18}O_3 \). This means they contain the same number of carbon, hydrogen, and oxygen atoms, but their structural arrangements can differ.

2. **Identifying Intermolecular Forces**:
- The boiling point of a substance is influenced by the strength of its intermolecular forces. Stronger intermolecular forces lead to higher boiling points.
- The primary types of intermolecular forces are hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Hydrogen bonding is the strongest among these.

3. **Analyzing the Compounds**:
- To have a higher boiling point, compound A should have stronger intermolecular forces compared to compound B. This can be achieved if A has more hydroxyl (-OH) groups (alcohols) compared to B, as alcohols can form hydrogen bonds.

4. **Considering Possible Structures**:
- Let's consider the possible structures for A and B:
- **Option 1**: A has 1 alcohol and 2 ethers; B has 2 alcohols and 1 ether.
- **Option 2**: A has 3 alcohols; B has 0 alcohols (3 ethers).
- **Option 3**: A has 3 ethers; B has 3 alcohols.
- **Option 4**: A has 2 alcohols and 1 ether; B has 1 alcohol and 2 ethers.

5. **Evaluating Each Option**:
- **Option 1**: B has more alcohols than A, so B would have a higher boiling point. (Not valid)
- **Option 2**: A has 3 alcohols and B has none, which means A would have a significantly higher boiling point due to hydrogen bonding. (Valid)
- **Option 3**: A has 3 ethers and B has 3 alcohols, so B would have a higher boiling point. (Not valid)
- **Option 4**: A has 2 alcohols and B has 1 alcohol, so A would have a higher boiling point, but not as high as in Option 2. (Not the best option)

6. **Conclusion**:
- The best option is **Option 2**, where compound A has 3 alcohol groups and compound B has 0 alcohol groups (3 ethers). This configuration allows A to have a significantly higher boiling point due to the presence of hydrogen bonding.

### Final Structures:
- **Compound A**: A structure with 3 hydroxyl (-OH) groups (alcohol).
- **Compound B**: A structure with 3 ether groups.