Effects of partial solvation. The free-energy landscapes of the DA reaction between cyclopentadiene (CPD) and acrylonitrile (ALT) to form endo-type product were computed for the reaction in the bulk (Figure ), at air-water interface (Figure ), and in gas phase (Figure ) by performing AIMD+MetD simulations. The reaction proceeds through a pre-reaction complex (RC) and a transition state (TS) before forming the product (P) (Figure ). The computed internal free-energy barrier ∆G ‡ int, which equals G(TS) -G(RC), increases from 18.2 kcal/mol in the bulk to 19.2 kcal/mol at the air-water interface, and to 20.7 kcal/mol in the gas phase. This trend of an increasing barrier from bulk to the gas phase agrees rather well with our DFT calculations performed at a higher theory level (Figure ). The observation that the free-energy barrier associated with the reaction occurring at the interface being slightly higher than its bulk counterpart is consistent to previous works. We attribute the free-energy barrier difference between the air-water interface case and the bulk one to the different stabilization modalities of the RC and TSs. To prove this hypothesis, we have analysed the structures and computed the average number of hydrogen bonds (HBs), nHB, between the N-atom in ALT and the H-atom in water molecules surrounding RC and TS. In the bulk solution, nHB equals to 1.67 and 2.10 for RC and TS, respectively. At the air-water interface, instead, the respective values decrease to 1.48 and 1.82. In comparison, as the system transits from the bulk to the interface, the number of HBs surrounding the TS decreases more than that for the RC, indicating that the TS is destabilized more than the RC as a result of solvent molecule loss. This differential destabilization effect leads to a higher free-energy barrier at the interface. This observation aligns with previous findings. In a nutshell, our simulations indicate the barrier of DA reaction with a partially solvated state at the interface increases with respect to the bulk, so the partial solvation effect cannot be the source for the acceleration of the DA reaction in water microdroplets.