Why is the boiling point of 2-propanol lower than 1-propanol

In summary, the boiling point of 2-propanol is lower than 1-propanol due to its decreased surface area leading to weaker dispersion forces and a lower net permanent dipole moment towards the oxygen atom. This results in easier separation of molecules and a lower boiling point. Additionally, the presence of hydrogen bonding in both molecules further contributes to the difference in boiling points.
  • #1
Zayn
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0

Homework Statement



Why is the boiling point of 2-propanol lower than 1-propanol?

The Attempt at a Solution



Is this right?

Because 2-propanol has its hydroxyl group in the middle of the atom, the electrons are all moving to the centre of the atom as opposed to 1-propanol, which has the hydroxyl group to the side, moving the electrons towards one extreme of the molecule, causing it to act similarly to a magnet. Because 1-propanol has its hydroxyl to one side, the hydrogen bonds it forms can pack together more densely than with 2-propanol, requiring more kinetic energy (temperature) to break them apart, which translates to a higher boiling point.
 
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  • #2
Zayn said:
in the middle of the atom, the electrons are all moving to the centre of the atom

You mean a molecule, don't you?
 
  • #3
That explanation is unnecessarily convoluted. It really just comes down to increased disperson and dipole-dipole forces.

Take a look at 1-propanol.
Now take a look at 2-propanol.

They both have hydrogen bonding, dipole-dipole, and disperson forces. The catch is that 1-propanol has higher surface area leading to increased disperson forces in comparison to the latter molecule. In addition, the net permanent dipole moment towards the oxygen is also higher due to the molecular geometry in the linear hydrocarbon (1-propanol). These increased dispersion forces lead to it being harder to pull molecules apart, thus raising the boiling point of said molecule.

For future reference: these questions are a process of deduction based on the strength of the intermolecular forces.

Hydrogen bonding > Dipole-dipole > Dispersion

Dispersion is a force that all molecules have, dipole-dipole is only in polar molecules, and hydrogen bonding is only present in molecules where hydrogen is directly bonded to oxygen, fluorine, or nitrogen.

Try answering the questions in those orders eliminating them as you go. If both molecules have the same types of forces, as in our example above, evaluate based on the relative strength of those forces.

edit: being able to pack closer together is surely a factor as well as mentioned in the explanation you gave
 

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Related to Why is the boiling point of 2-propanol lower than 1-propanol

1. What is the difference between 1-propanol and 2-propanol?

The only difference between 1-propanol and 2-propanol is the position of the hydroxyl group. In 1-propanol, the hydroxyl group is attached to the first carbon atom, while in 2-propanol, it is attached to the second carbon atom.

2. Why does the position of the hydroxyl group affect the boiling point?

The position of the hydroxyl group affects the boiling point because it changes the overall molecular structure and the strength of intermolecular forces between molecules. In 2-propanol, the hydroxyl group is closer to the branching of the molecule, making it more compact and reducing the strength of intermolecular forces. This results in a lower boiling point compared to 1-propanol, where the hydroxyl group is farther from the branching and the molecules are more closely packed together, leading to stronger intermolecular forces and a higher boiling point.

3. How do intermolecular forces affect the boiling point?

Intermolecular forces are the attractive forces between molecules. The strength of these forces determines how easily a substance can change from a liquid to a gas (boiling) or from a solid to a liquid (melting). The stronger the intermolecular forces, the higher the boiling point will be.

4. Are there any other factors that can affect the boiling point?

Yes, there are other factors that can affect the boiling point of a substance. These include the size and shape of the molecule, the presence of functional groups, and the molecular weight. All of these factors can influence the strength of intermolecular forces and therefore, the boiling point of a substance.

5. Can the boiling point of 2-propanol and 1-propanol be predicted based on their molecular structures?

Yes, the boiling point of a substance can be predicted based on its molecular structure. Generally, molecules with stronger intermolecular forces will have higher boiling points. Therefore, 1-propanol, with its more linear structure and stronger intermolecular forces, will have a higher boiling point than 2-propanol, which has a more branched structure and weaker intermolecular forces.

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