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ChemWiki: The Dynamic Chemistry E-textbook > Development Details > Approaches > Demos > Additional Demos > Photochemical Bromination of an Alkane

Photochemical Bromination of an Alkane

 

Chemical Concepts Demonstrated

  • Light-catalyzed reactions
  • Thermolytic and photolytic reactions
  • Free-radical reactions
  • Reactivity of alkanes

Demonstration

  • The two crystallizing dishes contain pentane and pentene and are placed on the overhead projector.
  • Bromine in dichloromethane is added to both of the dishes.
photo.gif

Observations

The pentene changes to colorless very quickly.  The pentane changes after exposure to the overhead's light.

Explanation (including important chemical equations)

The light-catalyzed reaction between an alkane and bromine can be stated as follows:

Chain initiation:       Br+ hv --> 2 Br.

Chain propogation:  Br+ R-H --> R-Br + H.

                              H+ Br--> H-Br + Br.

Chain termination:    2 Br--> Br2

                              2 H--> H2

                              H+ Br--> HBr

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Last Modified
10:29, 2 Oct 2013

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