Substitution Reaction Definition

by Anne Marie Helmenstine, Ph.D.
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.
Updated March 06, 2017

Definition: A substitution reaction is a type of chemical reaction where an atom or functional group of a molecule is replaced by another atom or functional group.

Examples: CH3Cl reacted with a hydroxy ion (OH-) will produce CH3OH and chlorine. This substitution reaction replaces the chlorine atom on the original molecule with the hydroxy ion.