SolutionsPhysical Properties
1. Order by boiling point
Order from lowest to highest boiling point: 1-chlorobutane, butane, 1-iodobutane and 1-bromobutane.
Butane (−0.5 °C) < 1-chlorobutane (78.4 °C) < 1-bromobutane (101.6 °C) < 1-iodobutane (130.5 °C).
Going down the halogen group, atomic weight and polarizability increase, and so do the London forces.
2. The fluoride
1-Fluorobutane boils at 32.5 °C. Why does it boil at a higher temperature than butane but at a lower one than 1-chlorobutane?
Compared with butane, the polar C–F bond adds dipole-dipole forces. Compared with 1-chlorobutane, fluorine is small and hardly polarizable, so its London forces are much weaker.
3. In the separating funnel
An aqueous solution is extracted with dichloromethane (density 1.33 g/mL). Which phase is at the bottom? And if diethyl ether (0.71 g/mL) is used?
With dichloromethane the organic phase is at the bottom, because it is denser than water. With diethyl ether the organic phase is on top.
4. Isomers
Which boils at a higher temperature, 1-bromobutane or 2-bromo-2-methylpropane? Why?
1-Bromobutane (101.6 °C versus about 73 °C). The linear chain has a larger contact surface between molecules than the branched, almost spherical one.