Illustrated Glossary of Organic Chemistry

Reaction coordinate: The x-axis of an energy profile, (or reaction profile) representing the progress along the reaction pathway (i.e., from reactants to products). Position along the reaction coordinate does not measure time or reaction rate, because individual reactants within the entire reaction react at different rates.

Energy profile for the SN2 reaction of CH3I with CH3O- (the reactants) to form CH3OCH3 and I- (the products). The reaction coordinate is shown in red.