Side species are components such as radicals that are important in the reactions connected on the path analysis diagram, but should not be characterized as source or target species on the reaction-path diagram. Common examples of such side species include the hydrogen radical, hydroxide radical, oxygen radical, and the peroxy radical. You can select which species should be designated as side species in the diagrams, using the tabs shown in Figure 4.6: Preferences panel.

Figure 4.12: Path diagram. With connections colored according to the presence of a side species in a reaction