Illustrated Glossary of Organic Chemistry

ΔG++: The difference in Gibbs free energy (G) between the transition state and the items on the left side of an equilibrium (such as reactants). ΔG++ = Gtransition state - Greactants.

This energy profile illustrates the difference between ΔG (which controls the reaction's equilibrium constant) and ΔG++ (which influences the reaction rate).