In explicit solvent, the reaction exhibits an earlier and more asynchronous TS compared to the implicit solvent or gas phase. The difference in bond length between the forming C-C bonds ∆r = |r 2 -r 1 | at the TS increases from 30 pm in the gas phase to 37 pm in implicit solvent and 46 pm in explicit water. Notably, explicit water molecules also altered the reaction mechanism from a concerted asynchronous to a "pseudo" stepwise mechanism, as evidenced by the presence of a shallow local minimum in the FESs immediately after the TS (Fig. ). This intermediate state, observed for both endo and exo reactions, corresponds to a zwitterionic state. Interestingly, such an intermediate is absent in the PES, where the structure corresponds to a high energy state (labelled as a cross in (Fig. )). This behaviour suggests that the intermediate arises from an entropic rather than an enthalpic contribution.