Herein, we propose a conceptually innovative approach to investigating reaction mechanisms. This study demonstrates the importance of considering explicitly the effects of large amplitude motions, aside from the intrinsic reaction coordinate, when tuning the free energy landscape of reaction pathways. We couple the path collective variables method with DFT-based enhanced sampling simulations to characterize the associative mechanism of the hydrolysis of the methyl phosphate dianion in solution. Importantly, energetics and mechanistic differences are observed when passing from the potential to the free energy surface.