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 S_N2 reaction of CH₃I with CH₃O^- (the reactants) to form CH₃OCH₃ and I^- (the products). The reaction coordinate is shown in red.