Module 2

Lesson 2.3  Substitution Reactions



Key Concepts


In a substitution reaction, a carbon-hydrogen bond in an alkane or benzene ring is broken and the hydrogen atom is replaced with another atom or group of atoms. Light, as a catalyst, is usually required for a substitution reaction to proceed at any appreciable rate. Other catalysts, such as FeCl3, may be used also.


Consider the following substitution reactions. Note that more than one product is formed.







In the third substitution reaction (shown below), note that more than one halogenated hydrocarbon is produced. Isomers are formed when alkanes longer than two carbon atoms undergo a substitution reaction.






  To better understand substitution reactions, read pages 421 to 422 in the textbook.

Check Your Understanding


Complete Practice Questions 8a, 8c, and 8e on pages 423 of the textbook.

Check your work by clicking on the link below.

Page 423 Practice Questions 8 a, c, e





  1. This is a substitution reaction.






  3. This is a substitution reaction.








  5. This is a substitution reaction.