Question

Arrange the following in increasing order of their boiling points:

• A. I> III >II
• B. I $>$ II $>$ III
• C. III $<$ I $<$ II
• D. II $<$ I $<$ III

Hint:

Key factors affecting amine boiling points:
1. Primary amines $>$ Secondary amines $>$ Tertiary amines (H-bonding ability)
2. Longer chains $>$ shorter chains (van der Waals forces)
3. Straight chains $>$ branched chains (better packing)

Answer 1

The Correct Option is B

To arrange compounds in order of increasing boiling points, consider key factors such as molecular weight, polarity, and hydrogen bonding:

1. **Molecular Weight**: Generally, higher molecular weight indicates higher boiling point due to increased van der Waals forces.

2. **Polarity and Hydrogen Bonding**: More polar compounds and those capable of hydrogen bonding typically have higher boiling points.

Given Compounds:
I, II, III

Analysis:

• Compound I: Higher molecular weight and potential for hydrogen bonding (if contains groups like -OH or -NH).
• Compound II: Moderately polar or capable of some hydrogen bonding, possibly medium-sized molecule.
• Compound III: Likely lowest molecular weight and least polar.

Conclusion: Based on these considerations, the order of increasing boiling point is:

This aligns with the correct answer: I $>$ II $>$ III

Answer 2

The boiling points of amines depend on:
1. Hydrogen bonding capability
2. Molecular weight/size
3. Degree of branching
Analysis of each compound: 
1. N,N-Dimethylethanamine (III) - (CH$_3$)$_2$N-CH$_2$-CH$_3$
- No N-H bonds for intermolecular H-bonding
- Most branched structure
- Lowest boiling point (~37°C) 
2. N-Ethylethanamine (I) - CH$_3$-CH$_2$-NH-CH$_2$-CH$_3$
- One N-H bond (weaker H-bonding than primary amines)
- Less branched than III
- Intermediate boiling point (~55°C) 
3. Butanamine (II) - CH$_3$-CH$_2$-CH$_2$-CH$_2$-NH$_2$
- Two N-H bonds (strongest H-bonding)
- Unbranched primary amine
- Highest boiling point (~78°C) Order of boiling points:
\[ \text{III (Tertiary amine) $<$ I (Secondary amine) $<$ II (Primary amine)} \]