Based on these works, some general trends can be deduced: First, pressure decreases the activation energy barrier until it eventually disappears (Figure ). Second, upon pressure application, the Diels-Alder Figure : Gibbs free energy profiles of the Diels-Alder reaction of cyclopentadiene and ethylene at different pressures, calculated with XP-PCM. Reproduced with permission from Chen et al., Copyright 2017, John Wiley and Sons.