Question

Explain the differences in boiling point of a 1-pentene (bp 30°c), 1-bromopentane (bp 129°c) and 1-pentanol (bp 137°c). what intermolecular forces are involved in holding the molecules in the liquid form in each of these as pure substances?

Answer 1

Generally bonds present between molecules are called intermolecular forces. they are three types:
1) Wander Wall forces (London forces)
2) Dipole - dipole interaction.
3) Hydrogen bond.
- As molecular weight increases boiling point also increases due to surface are is directly proportional to Wander Waal forces.
- Dipole-dipole attraction: the attraction between two different polarizable molecules is called dipole- dipole attraction, this attraction play important role in boiling point.
- Hydrogen bond: electrostatic attraction between hydrogen and more electronegative atom is called hydrogen bond.
- The substance which has hydrogen bond have higher boiling point.
1-pentanol has hydrogen bond
1- Bromopentane has dipole - dipole
1-pentene has only London forces
Hydrogen bond > dipole - dipole attraction > London force