The boiling point is a physical property of a substance that indicates the temperature at which it changes from a liquid to a gas at a specific pressure. It is influenced by several factors including the strength of intermolecular forces, molecular size, and molecular shape.

Intermolecular forces:
One of the main factors that affect the boiling point is the strength of intermolecular forces. Intermolecular forces are the attractive forces between molecules. The stronger the intermolecular forces, the higher the boiling point of the substance. The intermolecular forces can be categorized into three main types: London dispersion forces, dipole-dipole forces, and hydrogen bonding.

Molecular size:
The size of the molecule also plays a role in determining the boiling point. Generally, larger molecules have higher boiling points compared to smaller molecules. This is because larger molecules have more electrons and a greater number of intermolecular forces, resulting in stronger attractions between molecules.

Molecular shape:
The shape of the molecule can also affect the boiling point. Molecules with a more compact and symmetrical shape tend to have higher boiling points compared to molecules with a more elongated or asymmetrical shape. This is because a more compact shape allows for a closer packing of molecules, leading to stronger intermolecular forces.

Comparison of boiling points:
1. 2-propanol (isopropyl alcohol): The boiling point of 2-propanol is 82°C. It has a larger molecular size compared to propanone and 2-methyl propene, which contributes to its higher boiling point. Additionally, 2-propanol can form hydrogen bonds between its hydroxyl (-OH) groups and other molecules, further increasing the strength of intermolecular forces.

2. Propanone (acetone): The boiling point of propanone is 57°C. Propanone is a smaller molecule compared to 2-propanol and has a more symmetrical shape. Although it can form dipole-dipole interactions, it lacks hydroxyl groups for hydrogen bonding. These factors contribute to its lower boiling point compared to 2-propanol.

3. 2-methyl propene: The boiling point of 2-methyl propene is -7°C. 2-methyl propene is the smallest molecule among the three compounds and has an asymmetrical shape. It lacks functional groups for dipole-dipole interactions or hydrogen bonding. These factors result in weak intermolecular forces, leading to the lowest boiling point among the three compounds.

In summary, the boiling point of a substance is influenced by the strength of intermolecular forces, molecular size, and molecular shape. The higher boiling points of 2-propanol and propanone compared to 2-methyl propene can be attributed to their larger molecular sizes and ability to form stronger intermolecular forces.