Which compound will exhibit the lowest boiling point?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → N,N-dimethylethanamine
Reason (Boiling Point Order):
All compounds have similar molecular weight (~73 g/mol), so intermolecular forces decide the boiling point.
|
Compound |
Formula |
Type |
H-bonding? |
Approx. B.P. (°C) |
|
2. Butanol |
CH₃CH₂CH₂CH₂OH |
1° alcohol |
Yes (strong) |
117 |
|
3. Butanamine |
CH₃CH₂CH₂CH₂NH₂ |
1° amine |
Yes (moderate) |
78 |
|
1. Diethylamine |
(CH₃CH₂)₂NH |
2° amine |
Yes (moderate) |
56 |
|
4. N,N-Dimethylethanamine |
(CH₃)₂NCH₂CH₃ = (CH₃)₃N |
3° amine |
No |
~37–39 |
- Alcohols have strongest H-bonding → highest B.P.
- Primary amines → can form H-bonds → moderate B.P.
- Secondary amines → weaker H-bonding → lower B.P.
- Tertiary amines → no H-bonding → only van der Waals → lowest boiling point
Final Answer: N,N-Dimethylethanamine (also known as trimethylethanamine or simply trimethylamine) has the lowest boiling point.