The boiling point of:
(a) 1-propanol is 97 °C
(b) 1,2-propanediol is 214 °C and
(c) 1,2,3-propanetriol is 270 °C
What factors contribute to the increasing boiling points within the series?
The increasing boiling points within the series can be attributed to the increase in molecular weight and the number of hydrogen bonding sites. As the number of carbon atoms and/or the number of hydroxyl groups increase, so does the molecular weight and the ability to form more hydrogen bonds. This results in stronger intermolecular forces and a higher boiling point.
The factors that contribute to the increasing boiling points within the series of 1-propanol, 1,2-propanediol, and 1,2,3-propanetriol are primarily related to their molecular structures and intermolecular forces.
(a) 1-propanol: With a boiling point of 97 °C, 1-propanol is the lowest in the series. It has a longer carbon chain compared to the other compounds. The carbon chain provides more surface area for intermolecular forces to act upon. 1-propanol molecules can form hydrogen bonds between the hydroxyl (-OH) groups, which are the strongest type of intermolecular forces. These hydrogen bonds help to hold the molecules together, but they are not as strong as the other compounds in the series.
(b) 1,2-propanediol: With a boiling point of 214 °C, 1,2-propanediol has a higher boiling point than 1-propanol. The presence of two hydroxyl groups (-OH), one on each end of the molecule, allows for more intermolecular hydrogen bonding. This increased hydrogen bonding makes the intermolecular forces stronger, requiring more energy for the molecules to break apart and vaporize.
(c) 1,2,3-propanetriol: With a boiling point of 270 °C, 1,2,3-propanetriol has the highest boiling point in the series. It contains three hydroxyl groups (-OH), providing even more opportunities for extensive intermolecular hydrogen bonding. The increased number of hydrogen bonds results in stronger intermolecular forces, requiring even more energy to overcome and vaporize the compound.
In summary, the increasing boiling points within the series of 1-propanol, 1,2-propanediol, and 1,2,3-propanetriol can be attributed to the increasing number of hydroxyl groups, which allows for more extensive intermolecular hydrogen bonding and stronger intermolecular forces.