After TS1, the r C 1 -O LG increases, leading to an intermediate state, Inter1, adopting an (E 3 )-like ion conformation with r C 1 -O LG measuring 2.82 Å. Subsequently, TS2 links the (E 3 )-like and half-chair ( 4 H 3 )-like ion conformations (Inter2), in which C 1 , C 2 , C 5 and the ring oxygen defined the plane, with C 3 placed below and C 4 above it. This oxocarbenium Inter2 is 1.43 kcal mol -1 higher in energy than the RS (Fig. ). This intermediate consists of a contact ion pair, which is stabilized by hydrogen bond interactions (Fig. ). The stability of this ion pair was confirmed by 150 trajectories of 20 ps each (totalling 3 ns) using MLP-MD, demonstrating that r C 1 -O LG and r C 1 -O Nu oscillate around 3.7 Å (Fig. ) and confirming the formation of a contact ion pair.