91Ó°ÊÓ

Boiling point is defined as the temperature where a compound from its liquid state transforms into a gaseous state. More precisely, it is the temperature where pressure exerted by surroundings on the liquid is equal to the pressure exerted by the vapour of the liquid.

The forces that are key to measure the boiling point is

1. London Force: Depends on the area of contact, Higher the area of contact, higher will be the boiling point.
2. Vander waals Force
3. Induced Dipole Induced Dipole moment
4. Hydrogen bonding.

All of them are attractive forces. The more the attraction between the molecules, the more energy will be needed to separate them to boil. Thus, boiling point increases with these mentioned forces.

Intramolecular: H bonding within the atoms of same molecules.

Intermolecular: H bonding with the different molecules.

From the highest to lower boiling point is due to the H bonding seen in these compounds. 3 has 3 O-H bonds which is highest among all of them. So, the no of H bonding will be highest comparing 2 ,3 and 5 no structure. The order of boiling point between these 3 will be according to the no of O-H bonds.

As, in NH₃, no of H bonds are one where for O-H, it is 2, the extent of H bonding will be less in the former as well as the boiling point.

Between 1 and 4, As 4 is a branched chain, the surface area of it decreases which also decreases its boiling point.