24.2 Reactivity of Alkanes and Alkenes

Chemical Concepts Demonstrated: relative organic reactivity, bromination of alkenes


Two sets of crystallizing dishes are filled with each of the following:
  • cycloalkane
  • alkane
  • benzene
  • styrene

Bromine in dichloromethane solution is added to the first set, and potassium permanganate is added to the second.

Observations and Explanations:

    When the bromine is added, the styrene reacts very quickly because of the phenyl group.  The benzene does not react.  The alkanes do not react either, although prolonged exposure to an overhead projector will provoke a bromination (see demonstration 24.3).  It should be noted that alkenes and alkynes react with bromine to form dibromides.

    When the potassium permanganate is added, styrene and benzene are oxidized.  Alkenes are oxidized to diols and alkynes are oxidized to diones.   The alkanes in this situation do not react with the potassium permanganate.