Question:
Arrange the following in decreasing order of their boiling points
Arrange the following in decreasing order of their boiling points
Show Hint
Greater intermolecular hydrogen bonding leads to higher boiling point:
\[
\text{Alcohols}\gt \text{1° amines}\gt \text{2° amines}\gt \text{3° amines}
\]
because tertiary amines lack \(N-H\) bonds.
Updated On: Jun 22, 2026
- \(a\gt b\gt d\gt c\)
- \(a\gt c\gt d\gt b\)
- \(b\gt c\gt d\gt a\)
- \(c\gt a\gt b\gt d\)
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The Correct Option is A
Solution and Explanation
Step 1: Compare intermolecular hydrogen bonding.
Boiling point mainly depends on the strength of intermolecular forces.
Alcohols contain: \[ -OH \] group which forms very strong intermolecular hydrogen bonding.
Therefore, alcohols generally have the highest boiling points among compounds of comparable molecular masses.
Hence, \[ a \] has the highest boiling point.
Step 2: Compare primary, secondary and tertiary amines.
Primary amines contain two hydrogen atoms attached to nitrogen: \[ RNH_2 \] Hence, they show maximum intermolecular hydrogen bonding among amines.
Secondary amines: \[ R_2NH \] contain only one hydrogen attached to nitrogen, so hydrogen bonding is less than primary amines.
Tertiary amines: \[ R_3N \] have no hydrogen attached to nitrogen and therefore cannot form intermolecular hydrogen bonding effectively.
Thus, their boiling point is the lowest among the three.
Step 3: Arrange in decreasing order.
Therefore, the boiling point order is: \[ \text{Alcohol}\gt \text{Primary amine}\gt \text{Secondary amine}\gt \text{Tertiary amine} \] That is, \[ a\gt b\gt d\gt c \]
Step 4: Final conclusion.
Hence, the decreasing order of boiling points is \[ \boxed{a\gt b\gt d\gt c} \]
Boiling point mainly depends on the strength of intermolecular forces.
Alcohols contain: \[ -OH \] group which forms very strong intermolecular hydrogen bonding.
Therefore, alcohols generally have the highest boiling points among compounds of comparable molecular masses.
Hence, \[ a \] has the highest boiling point.
Step 2: Compare primary, secondary and tertiary amines.
Primary amines contain two hydrogen atoms attached to nitrogen: \[ RNH_2 \] Hence, they show maximum intermolecular hydrogen bonding among amines.
Secondary amines: \[ R_2NH \] contain only one hydrogen attached to nitrogen, so hydrogen bonding is less than primary amines.
Tertiary amines: \[ R_3N \] have no hydrogen attached to nitrogen and therefore cannot form intermolecular hydrogen bonding effectively.
Thus, their boiling point is the lowest among the three.
Step 3: Arrange in decreasing order.
Therefore, the boiling point order is: \[ \text{Alcohol}\gt \text{Primary amine}\gt \text{Secondary amine}\gt \text{Tertiary amine} \] That is, \[ a\gt b\gt d\gt c \]
Step 4: Final conclusion.
Hence, the decreasing order of boiling points is \[ \boxed{a\gt b\gt d\gt c} \]
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