Arrange the following sets of compounds in order of their increasing boiling points:
A: Pentan-1-ol, butan-1-ol, butan-2-ol, ethanol, propan-1-ol, methanol
B: Pentan-1-ol, n-butane, pentanal, ethoxyethane
Arrange the following sets of compounds in order of their increasing boiling points:
A: Pentan-1-ol, butan-1-ol, butan-2-ol, ethanol, propan-1-ol, methanol
B: Pentan-1-ol, n-butane, pentanal, ethoxyethane
A:
Factors affecting boiling point
1. Number of carbon atoms:
As the number of carbon atoms increases in alcohol molecule, the boiling point of alcohol also increases as the molecular mass increases which increases the molecular attraction between molecules.
2. Branching in molecules:
As the number of branching increases, the boiling point of alcohol decreases because branching in molecules decreases the surface area thereby decreasing the attractive forces between individual molecules.
Boiling point order
a: CH3−CH2−CH2−CH2−OH
Pentan −1 −ol
b: CH3−CH2−CH2−CH2−OH
Butan −1 −ol
c:
Butan−2−ol
d:
Ethanol
e: 
Propan−1−ol
f: CH3−OH
Methanol
Increasing order of boiling point:
Methanol < Ethanol < Propan-1-ol < Butan-2-ol < Butan-1-ol < Pentan-1-ol
B:
Factors affecting boiling point
1. Number of carbon atoms:
As the number of carbon atoms increases in alcohol molecule, the boiling point of alcohol also increases as the molecular mass increases which increases the molecular attraction between molecules.
2. Branching in molecules:
As the number of branching increases, the boiling point of alcohol decreases because branching in molecules decreases the surface area thereby decreasing the attractive forces between individual molecules.
3. Hydrogen bonding:
As the extent of hydrogen bonding increases, the boiling point also increases due to increase in the attractive forces between individual molecules.
Boiling point order
a:
Pentan−1−ol
b:CH3−CH2−CH2−CH3
n−butane
c: 
Pentanal
d: CH3−CH2−OCH2−CH3
Ethoxy ethane
If pentan-1-ol and pentanal are compared, both compounds have almost same molecular mass so, similar London forces. Moreover, dipole-dipole interactions are also similar in both the compounds only hydrogen bonding is making a difference as extent of intermolecular hydrogen bonding is greater in case of pentan-1-ol than pentanal. Hence, boiling point of pentan-1-ol is greater than pentanal.
Hence considering all factors, increasing order of boiling point will be:
n-butane < ethoxyethane < pentanal < pentan-1-ol
Factors affecting boiling point
1. Number of carbon atoms:
As the number of carbon atoms increases in alcohol molecule, the boiling point of alcohol also increases as the molecular mass increases which increases the molecular attraction between molecules.
2. Branching in molecules:
As the number of branching increases, the boiling point of alcohol decreases because branching in molecules decreases the surface area thereby decreasing the attractive forces between individual molecules.
Boiling point order
a: CH3−CH2−CH2−CH2−OH
Pentan −1 −ol
b: CH3−CH2−CH2−CH2−OH
Butan −1 −ol
c: Butan−2−ol
d: Ethanol
e: Propan−1−ol
f: CH3−OH
Methanol
Increasing order of boiling point:
Methanol < Ethanol < Propan-1-ol < Butan-2-ol < Butan-1-ol < Pentan-1-ol
B:
Factors affecting boiling point
1. Number of carbon atoms:
As the number of carbon atoms increases in alcohol molecule, the boiling point of alcohol also increases as the molecular mass increases which increases the molecular attraction between molecules.
2. Branching in molecules:
As the number of branching increases, the boiling point of alcohol decreases because branching in molecules decreases the surface area thereby decreasing the attractive forces between individual molecules.
3. Hydrogen bonding:
As the extent of hydrogen bonding increases, the boiling point also increases due to increase in the attractive forces between individual molecules.
Boiling point order
a:Pentan−1−ol
b:CH3−CH2−CH2−CH3
n−butane
c: Pentanal
d: CH3−CH2−OCH2−CH3
Ethoxy ethane
If pentan-1-ol and pentanal are compared, both compounds have almost same molecular mass so, similar London forces. Moreover, dipole-dipole interactions are also similar in both the compounds only hydrogen bonding is making a difference as extent of intermolecular hydrogen bonding is greater in case of pentan-1-ol than pentanal. Hence, boiling point of pentan-1-ol is greater than pentanal.
Hence considering all factors, increasing order of boiling point will be:
n-butane < ethoxyethane < pentanal < pentan-1-ol
