1
Question
Arrange the following compounds in the increasing order of their boiling points:
CH3CH2CH2CHO, CH3CH2CH2CH2OH, H5C2−O−C2H5, CH3CH2CH2CH2CH3
CH3CH2CH2CHO, CH3CH2CH2CH2OH, H5C2−O−C2H5, CH3CH2CH2CH2CH3
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Solution
Factors affecting boiling points
1. Number of carbon atoms in hydrocarbon:
The boiling point of the hydrocarbon increases with the increase in the carbon atoms and the increase in the molecular weight as due to increase in size of the molecule, intermolecular forces of attraction increases.
2. Hydrogen bonding:
Due to intermolecular H−bonding between molecules, intermolecular forces of attraction increases and the compounds which can form intermolecular H−bonding have higher boiling point.
The number of carbon atoms and molecular masses of all these compounds are same. So, this is not the deciding criteria for the difference between the boiling points of these compounds.
Since, only butan−1−ol molecules are associated with intermolecular hydrogen bonding, therefore, the boiling point of
butan−1−ol would be the highest.
Now, if butanal and ethoxyethane is compared, butanal is more polar, hence can be said that there will be more dipole-dipole interactions between butanal molecules. Therefore, the boiling point of butanal is higher than that of ethoxyethane.
There will be only weak London forces exist between butane molecules, so boiling point of butane is least amongst given four compounds.
Increasing order of boiling points
Order of boiling point can be given as:
CH3CH2CH2CH3 < H5C2−O−C2H5 < CH3CH2CH2CHO < CH3CH2CH2CH2OH
1. Number of carbon atoms in hydrocarbon:
The boiling point of the hydrocarbon increases with the increase in the carbon atoms and the increase in the molecular weight as due to increase in size of the molecule, intermolecular forces of attraction increases.
2. Hydrogen bonding:
Due to intermolecular H−bonding between molecules, intermolecular forces of attraction increases and the compounds which can form intermolecular H−bonding have higher boiling point.
The number of carbon atoms and molecular masses of all these compounds are same. So, this is not the deciding criteria for the difference between the boiling points of these compounds.
Since, only butan−1−ol molecules are associated with intermolecular hydrogen bonding, therefore, the boiling point of
butan−1−ol would be the highest.
Now, if butanal and ethoxyethane is compared, butanal is more polar, hence can be said that there will be more dipole-dipole interactions between butanal molecules. Therefore, the boiling point of butanal is higher than that of ethoxyethane.
There will be only weak London forces exist between butane molecules, so boiling point of butane is least amongst given four compounds.
Increasing order of boiling points
Order of boiling point can be given as:
CH3CH2CH2CH3 < H5C2−O−C2H5 < CH3CH2CH2CHO < CH3CH2CH2CH2OH
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