In the given pair of compounds, in which pair second compound has higher boiling point than first compound ?

Options

A.
B.
C. `HO - CH_2-CH_2 - OH and CH_3 - CH_2 - CH_2 - OH`
D.

Explanation

To determine which pair of compounds has the second compound with a higher boiling point than the first compound, we can analyze the boiling points based on hydrogen bonding and dipole-dipole interactions. Here’s a step-by-step solution:

### Step 1: Understand the Factors Affecting Boiling Points
- Boiling points are influenced by hydrogen bonding, dipole moments, and molecular interactions.
- Compounds with strong hydrogen bonding typically have higher boiling points.
- Dipole-dipole interactions also contribute to the boiling point, especially when there is a significant electronegativity difference between atoms.

**Hint:** Remember that hydrogen bonding occurs when hydrogen is attached to highly electronegative atoms like oxygen, nitrogen, or fluorine.

### Step 2: Analyze Each Pair of Compounds
1. **First Pair: Cyclopropyl Alcohol vs. Ether**
- Cyclopropyl alcohol has an -OH group, allowing for significant hydrogen bonding.
- Ether lacks hydrogen bonding to the same extent.
- **Conclusion:** Cyclopropyl alcohol has a higher boiling point.

2. **Second Pair: Two Compounds with Different Dipole Moments**
- The first compound has a significant dipole moment due to electronegative atoms.
- The second compound has no significant electronegativity difference.
- **Conclusion:** The first compound has a higher boiling point.

3. **Third Pair: Two Compounds with Different -OH Groups**
- The first compound has two -OH groups, leading to more hydrogen bonding.
- The second compound has one -OH group.
- **Conclusion:** The first compound has a higher boiling point.

4. **Fourth Pair: Tertiary Amine vs. Secondary Amine**
- The tertiary amine (NCH3) has steric hindrance, reducing hydrogen bonding.
- The secondary amine (NH) has a greater extent of hydrogen bonding.
- **Conclusion:** The secondary amine has a higher boiling point.

### Step 3: Identify the Correct Pair
- From the analysis, the only pair where the second compound has a higher boiling point than the first is the **fourth pair** (tertiary amine vs. secondary amine).

**Final Answer:** The correct answer is **option 4**, where the second compound (secondary amine) has a higher boiling point than the first compound (tertiary amine).