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Substitution
A third important type of reaction for alkanes is the substitution reaction, an example of which is shown here and in example 19 in your workbook. Notice that this kind of reaction is the equivalent of the double displacement (or double replacement) reactions you studied last term.
Notice in this example that the highlighted hydrogen atom ends up bonded to one of the two chlorine atoms. One of the two chlorine atoms is substituted for the highlighted hydrogen atom. Although any hydrogen atom in an alkane can be involved in a substitution reaction, the molecules do have certain preferences for which are most likely to be substituted. We won't deal with what those preferences are in this course. Notice that in this substitution reaction, only one of the chlorine atoms becomes bonded to the organic molecule. The other becomes bonded to the hydrogen atom that leaves the organic molecule. High temperatures or high energy ultraviolet light is generally needed to provide the activation energy for this kind of reaction. Chlorine (Cl2) is not the only chemical that can be involved in substitution reactions. There are a number of others including bromine (Br2) and the other halogens.
E-mail instructor: Eden Francis Clackamas Community College |
